0:05

Hello, you're listening to Wine Blast

0:07

with me, Susie Barry, and my

0:09

husband and fellow Master of Wine,

0:12

Peter Richards. And in this episode,

0:14

we're going to dive, headfirst, into

0:17

a glass of wine and wallow

0:19

around a bit. No change from

0:21

normal there, you might say, but

0:24

no, this is proper work. proper

0:26

research because we are going to

0:28

uncover the astonishing reality of just

0:31

how complex and fascinating the chemistry

0:33

of wine is. The very

0:36

finest kind of complex chemical

0:38

soup which as we become

0:40

clear is still something of

0:42

a wonderful mystery. Talking of

0:45

which in this show we're

0:47

going to touch on everything

0:49

from flowers to cigarettes. Farting,

0:52

petrol, AI, whiskey, urine and

0:54

strawberry flavoured yogurt. Here's a

0:56

taster of what's coming up.

0:59

We should not just look

1:01

at chemical compounds and think

1:03

about the impact of this compound

1:05

on its own. It's more of

1:08

our job to just enjoy what

1:10

it is in a glass as

1:12

a whole complex matrix. AI can

1:14

certainly not do that yet. Goshu

1:16

there, the first Chinese master of

1:19

wine who works in the US

1:21

as a wine chemist and sensory

1:23

scientist. Guss has just published a...

1:26

brilliant book called Behind the Glass,

1:28

The Chemical and Sensorial Tower of

1:30

Wine Tasting. We'll have a discount

1:32

code for that at the end

1:35

of the show. Gus says, and

1:37

I quote, behind every glass of

1:39

wine there is science. But note,

1:42

in that snippet you've just

1:44

heard, how he also talks

1:46

about enjoyment. So Gus is

1:48

going to be our genial,

1:50

white-coated guide to this intriguing

1:52

world of flavor. chemistry, there

1:54

may even be a little

1:56

experiment along the way. Oh, I love

1:59

the sound of that. blow stuff up. Obviously

2:01

the best bits of chemistry at school

2:03

were sort of blowing stuff up, wouldn't

2:05

it? I'm not sure how we can

2:07

shoehorn blowing stuff up into wine experiments.

2:09

You know, I'm gonna... I'm gonna live

2:12

in hope. I'm gonna live in hope.

2:14

I'm gonna live in hope on that

2:16

one. Anyway, the reason we're doing this

2:18

episode is we had a listener question

2:20

in from Ellen Pranta who's from Sweden

2:23

who writes as follows. Hi guys, thank

2:25

you so much for one of the

2:27

best podcast podcast podcast ever. Now I

2:29

love wine and I can't stop asking

2:31

the question why when starting to

2:34

learn about wine I was told

2:36

that Cabanet serving your smells of

2:38

black currants. My first question then

2:40

became... Why does the Cabernet family

2:42

of grapes have the aroma of

2:44

black currants? What compounds come from

2:46

the grape which are created during

2:49

different stages of wine making? I

2:51

would love to hear you talk

2:53

more about wine chemistry in your

2:56

nerdy but easy and understandable way.

2:58

I find it fascinating where in

3:00

the process the famous aromas of

3:03

some styles of wine occur and

3:05

the chemistry behind it. Nurdie but

3:07

understandable. I think that's a

3:09

complement. But no, I mean, what a

3:12

great question. Thank you, Ellen. We did

3:14

touch a bit on chemistry in our

3:16

recent episode on wine faults. And we

3:18

also did an episode back in season

3:20

three on the magical science of taste.

3:22

But this is a bit different. As

3:24

Gus says, there is science behind every

3:26

glass of wine, and this is a

3:29

great excuse to explore that a bit

3:31

more. What Gus also says, literally on

3:33

page one of his book, is that

3:35

he's often asked to explain the science

3:38

behind why a wine taste the way

3:40

it does. and he says, there's no

3:42

short answer. First, he points out that

3:45

chemically, wine is one of the most

3:47

complex solutions in the world. And secondly,

3:49

not only are human senses among the

3:52

least understood subjects in the scientific world,

3:54

but we're all different. So the same

3:56

glass of wine can be perceived in

3:58

very different ways. ways by different

4:00

people. Yeah he writes it turns

4:03

the seemingly simple question why does

4:05

it taste that way into a

4:07

surprisingly complex one. Okay so we've

4:09

got our complexity and subjectivity disclaimers

4:11

out of the way early but

4:13

we do like answers on wine

4:15

blast as much as questions and

4:18

Gus provides lots of those so

4:20

that's going to give us plenty

4:22

of good material to work with

4:24

to answer Ellen's questions. To summarize

4:26

though there are two things going

4:28

on here. the chemistry in the

4:30

glass which comes from grapes and

4:32

microbes and wine making and aging

4:35

etc. and then our personal interaction

4:37

with the wine. Gus defines these

4:39

as the chemical terroir of a

4:41

wine, i.e. what's in the glass,

4:43

as distinct from the sensorial... tell

4:45

what essentially what we make of

4:47

that chemistry. Yeah so we'll explain

4:50

and explore this a bit more

4:52

in due course in case your

4:54

head is already started to spin

4:56

but these are really important distinctions

4:58

to make from the outset to

5:00

to frame our discussion if you

5:02

like. Now Gassa's book itself is

5:04

structured around the human senses starting

5:07

off with sight I you know

5:09

how wine looks and then moving

5:11

on to taste so that's where

5:13

we started to I ask us

5:15

how he would describe a glass

5:17

of red wine to me analytically

5:19

in terms of chemical components. So

5:22

the color we can see in

5:24

red are from anthosynons and that's

5:26

very chemical and people may find

5:28

it boring but once I link

5:30

that to real life situations like

5:32

almost all flowers we see in

5:34

the field of fruits when they

5:36

are red or purpleish in color

5:39

they are coming from anthosynins. So

5:41

again, we can see that, right?

5:43

So I say anthosynus. Maybe some

5:45

people may feel it's a bit

5:47

complicated, but actually you can connect

5:49

it into your daily life. And

5:51

then tenants, are those astringent compounds

5:54

we can perceive in the red

5:56

wine? And if you don't know,

5:58

tenants. drink tea and teas are

6:00

filled with full of tannins or

6:02

eat raw bananas, right? You can

6:04

feel that a stringent drying mouth

6:06

feel. And why, so let's say,

6:08

do we get more complicated, why

6:11

are those compounds there? Why are

6:13

flowers red, why are red grapes

6:15

red in terms of colour? And

6:17

then why do they have these

6:19

talons that we can perceive in

6:21

our mouths as well? Yeah, it's

6:23

a... a bit complicated but in

6:26

general is more about how those

6:28

flowers and fruits serve their main

6:30

functionality which is reproduction. So to

6:32

pass down the genetics to survive

6:34

in nature they have certain colors

6:36

either to protect them or to

6:38

let them be attractive to humans

6:41

or animals to eat and help

6:43

them spread seeds. and those are

6:45

all about nature. So in my

6:47

book, I really try to deliver

6:49

one message is to appreciate nature

6:51

and try to smell and eat

6:53

and drink as many things as

6:55

you can so that you can

6:58

actually connect what's around you into

7:00

a glass of wine. So wine

7:02

professionals aren't any more gifted than

7:04

anyone else. They just paid more

7:06

attention to the smells and the

7:08

tastes around them and given them

7:10

names and then you couldn't suddenly

7:13

do it. Exactly and honestly, I

7:15

found out that at least around

7:17

me, those people who love to

7:19

eat and drink all sorts of

7:21

things, they tend to be better

7:23

wine tasters. So we have official

7:25

scientific advice to smell and eat

7:27

and drink as many things as

7:30

we can. Happy days. But you

7:32

can see exactly what he's saying,

7:34

you know, wine captures so many

7:36

things in one glass, all of

7:38

which can be found in the

7:40

natural world around us. And we

7:42

can train ourselves to... Learn this

7:45

language of taste and scent by

7:47

repeated exposure. Yeah, you know, it

7:49

does compare it to learning a

7:51

new language in his book, because,

7:53

you know, it's difficult connecting words

7:55

to smells and taste and sensations,

7:57

isn't it? You know, equally though,

7:59

you know, it's not impossible. And

8:02

it's actually quite fun to learn,

8:04

too. Now, talking of fun, for

8:06

me, it isn't real science if

8:08

you can't do experiments. And Gus

8:10

did suggest one in terms of

8:12

colour. Oh, does it involve explosions?

8:14

You know, do I need to

8:17

put my safety goggles on? Oh,

8:19

safety never takes a day off.

8:21

You know, I'm disappointed if you

8:23

don't wear safety goggles, to be

8:25

honest. Permanently. You know, you wear

8:27

them so well. No, no, sadly,

8:29

no explosions. That is not a

8:31

compliment. Unless you're talking about explosions

8:34

of color, that is, because that's

8:36

where we're going. Because Gus mentioned

8:38

anthosynins there, which is a group

8:40

of compounds that belong to a

8:42

large category called phenolics, which... make

8:44

wines more interesting both in terms

8:46

of chemistry and also taste. Now

8:49

we've talked about this before on

8:51

the pod, haven't we? And we

8:53

also mentioned it in our recent

8:55

episode on the vines of the

8:57

future. And this is a point

8:59

that Gus makes in his book

9:01

too, how all grapes historically are

9:03

thought to have been dark colored.

9:06

So red or black, however you

9:08

want to term it. probably to

9:10

catch the eye of animals who

9:12

might eat them and help distribute

9:14

the seeds in their boo, thereby

9:16

helping the vine reproduce and spread.

9:18

Yeah, and then white or paler

9:21

skin, great varieties, are more recent

9:23

mutations, right? You know, the key

9:25

difference being the specific anthocyanins. in

9:27

red grapes absorb other wavelengths of

9:29

light but reflect the reddish wavelengths

9:31

into our eyes. Unless we have

9:33

issues with colour blindness. Yeah. But

9:35

that's a whole other discussion which

9:38

Gus does actually explore in his

9:40

book, doesn't he? He does, among

9:42

many other things. So anyway, you

9:44

know, various things can influence a

9:46

wine's colour. One is how acidic

9:48

or not the wine is. In

9:50

other words, it's pH. So this

9:53

is a good way to observe

9:55

wine chemistry. in action. So if

9:57

you grab a glass of red

9:59

wine, if you slowly add tap

10:01

water, hence lessening the acidity or

10:03

raising the pH, the colour in

10:05

the wine, if you look carefully,

10:07

will change from more red to

10:10

more blue. purple in theory if

10:12

you then add something acid back

10:14

in like let me use for

10:16

example and lower the pH in

10:18

doing so the color should revert

10:20

back to more red so you

10:22

know I'm seeing a virtual disco

10:25

ball in my wine glass right

10:27

there Boom. What is it with

10:29

you in disco balls? But this

10:31

difference in colour is due to

10:33

different forms of anthocyanins being present

10:35

at different pH levels right. So

10:37

a visual representation of the chemistry

10:39

in the glass. I mean it's

10:42

the same with flowers isn't it?

10:44

Gus talks about a Brazilian flower

10:46

that can change colour from purple

10:48

to lavender to white in just

10:50

a few days. because the plant

10:52

changes the pH which influences the

10:54

color of the anthosioners. Yeah yeah

10:57

that's right and you know as

10:59

humans we're primarily visual creatures so

11:01

this kind of thing is is

11:03

important but we also mentioned taste

11:05

there and Gus touched on tannins

11:07

in red wine and now our

11:09

palate is the last checkpoint for

11:11

toxicity when it comes to food

11:14

so our tongue and mouth are

11:16

crucial to our survival but you

11:18

know I think We often underestimate

11:20

its powers and potential. I agree,

11:22

I agree, yeah. And in the

11:24

book, Gus does a great job

11:26

of giving an up-to-date understanding of

11:29

human palate perception. And that understanding

11:31

has changed a fair bit over

11:33

the years and probably will, hopefully

11:35

will, in the future. And for

11:37

example, that old chestnut of the...

11:39

tongue map where tastes are supposedly

11:41

sensed on different parts of the

11:43

tongue so sweet at the front,

11:46

bitter at the back, sour and

11:48

salty at the sides. That has

11:50

absolutely been proven to be false.

11:52

Our tongue has loads of papilli

11:54

all over its surface which house

11:56

our taste buds which can in

11:58

turn detect... all the different tastes.

12:01

And not... So each taste bug

12:03

can detect all the different... Exactly,

12:05

yeah, and it's all over. So

12:07

it's not just the basic, you

12:09

know, five of salt, sweet, sour,

12:11

bitter, umami, probably more too. And

12:13

fat, for example. Yeah, yeah, and

12:15

bitterness, which you mentioned here, can

12:18

indicate poison free. But, you know,

12:20

I find it interesting because, you

12:22

know, we can tolerate a bit

12:24

of it and can even learn

12:26

to like it. You know, for

12:28

example, because it can make things

12:30

taste more, more interesting, especially, you

12:33

know, as we get older. For

12:35

example, like tannins and wine, that's

12:37

how we can get a taste

12:39

for those. But then personal perception

12:41

of bitterness is one of the

12:43

things that can vary most between

12:45

people. painfully disgusting. That's where you

12:47

taste, you sort of bury sensitive.

12:50

Yeah, so sensitive and sensitive, but

12:52

then for hypertasters, as opposed to

12:54

hypertasters, the same level of bitterness

12:56

in a food or tannin and

12:58

a wine is absolutely fine. Apparently,

13:00

women tend to be more sensitive

13:02

towards bitterness and sour and salty

13:05

tastes than men, and then young

13:07

people are generally more sensitive than

13:09

older people. You're trying to tell

13:11

me men are just not very

13:13

sensitive people? Old men. old men

13:15

that can take as much bitterness

13:17

as they eat. That's a lot

13:19

of bitterness. You can throw at

13:22

them. Let's move on. But you

13:24

know it's also interesting genetics can

13:26

also influence the way you can

13:28

taste in another really interesting way.

13:30

For example the composition and production

13:32

or flow of saliva varies significantly

13:34

between people. Now this can affect

13:37

the perception of tannin. Tanins produce

13:39

a drying and astringent sensation because

13:41

they reduce or remove the lubricating

13:43

functionality of saliva proteins. So if

13:45

you have more saliva, it's likely

13:47

the wine will taste less tannic.

13:49

And it's the same with the

13:51

perception of saltiness too, isn't it?

13:54

You know, our saliva is naturally

13:56

slightly salty or it contains sodium

13:58

ions. If something tastes salty, it's

14:00

because it has a higher concentration

14:02

of sodium ions than what's in

14:04

our saliva. But if your saliva

14:06

naturally or at that moment in

14:09

time has a higher sodium ion

14:11

concentration than mine, then we'll perceive

14:13

that level of saltiness very differently.

14:15

This is getting a bit weird.

14:17

It does a bit. I mean,

14:19

and then we're married. But you

14:21

know, even then, discussing the saltiness...

14:23

your saliva versus mine is so

14:26

I don't know which thing is

14:28

dangerous territory I just think it's

14:30

dangerous even if it is interesting

14:32

in terms of salinity and wife

14:34

I say let's move on do

14:36

you think I think move on

14:38

there we go from spit to

14:41

my mind it's the bits about

14:43

aroma in Gus's book that I

14:45

find most interesting and I think

14:47

that's what Ellen was driving at

14:49

in her question too Gus says

14:51

that theoretically we humans can detect

14:53

a trillion different smells. But it's

14:55

not certain, plus anyway, our olfactory

14:58

vocabulary is limited. Certainly don't have

15:00

a trillion words for aromas, do

15:02

you? No, no. Black currents, black

15:04

currents, black currents, isn't it? So,

15:06

you know, so what are these

15:08

smells in wine and how do

15:10

we interact with them? I asked

15:13

Gus, how many aroma compounds there

15:15

are in a glass of wine?

15:17

That's very interesting because if you

15:19

ask the flavor chemist, they may

15:21

tell you that at the moment,

15:23

we might have found out probably

15:25

hundreds of aroma compounds already in

15:27

wine. But in my opinion, there

15:30

could be thousands or even more.

15:32

What's interesting is that, for example,

15:34

I analyze TCA, which is a

15:36

compound that cotent, right, in cork

15:38

or in wine or in other

15:40

products. But those compounds, they are

15:42

at parts per trillion level. Meaning

15:45

that if you have let's say

15:47

two units in a trillion in

15:49

that kind of concentration, we can

15:51

smell them. Meaning there could be

15:53

compounds like TCA that is extremely

15:55

low in concentration, but they have

15:57

a huge sensory impact. And we

15:59

actually will see more and more

16:02

of those kind of compounds being

16:04

discovered by scientists, I believe, over

16:06

the next five, ten or twenty

16:08

years. So the truth is we

16:10

really don't know how many aroma

16:12

compounds there are in a glass

16:14

of wine right now. Especially the

16:17

small ones, but yet they have...

16:19

huge sensory impact. Fascinating. Okay, so

16:21

let's let's let's get down to

16:23

basics. I've got a glass of

16:25

peppery sira in front of me,

16:27

doesn't matter where it's from, talk

16:29

me through that in terms of

16:31

the chemistry of those typical aromas

16:34

that we're going to find in

16:36

that class. Okay, so for the

16:38

fruity aromas, we might save that

16:40

for later because there's a huge

16:42

group of them, but for the

16:44

peppery notes, it belongs to a

16:46

big group of compounds that we...

16:49

find in nature, as always. They

16:51

are called terpenoids, and some wind

16:53

industry people call them terpings, which

16:55

is actually a smaller subgroup of

16:57

terpenoids, but if you say terpenoids

16:59

or terpins, however you see it,

17:01

we understand, right? And those terpings,

17:03

I tell you, it has probably

17:06

hundreds of different expressions. Cigarettes. They

17:08

are filled with terpings. and hops

17:10

in beer they are filled with

17:12

terpings. And wine, of course we

17:14

have lots of wines that have

17:16

lots of terpings like muscat grape.

17:18

Those kind of floral aromas from

17:21

muscat, they are terpenoids. So for

17:23

sira, the pepperinoes is one type

17:25

of terpanoi. Just to think about

17:27

how diverse the terpine or terpenoid

17:29

world is. So just to interject

17:31

here, we should firstly explain that

17:33

Gus's current day job involves him

17:35

studying TCA, the compound behind Cork

17:38

taint, hence that connection. But in

17:40

terms of the discussion here, Gus

17:42

is talking about rotundone, right? In

17:44

terms of the peppery character in

17:46

Syria, like you find in Kertrouti

17:48

or hermitage in France or Swatland

17:50

in South Africa or San Antonio

17:53

in Chile. Yeah, exactly, exactly. Now,

17:55

rotundone is a turpenoid that gives

17:57

the black pepper aroma. Now interestingly,

17:59

this chemical compound was only recognised

18:01

as the active aroma contributor in

18:03

actual peppercorns as a result of

18:05

Australian researches identity. in their sirets.

18:07

Love it. Love it. Love it.

18:10

A good example of wine leading

18:12

the way as it does in

18:14

so many fields, but in particular

18:16

flavor chemistry there. But terpenoids are

18:18

hugely diverse as Gus said. So

18:20

I asked him what other examples

18:22

of terpenoids might we commonly come

18:25

across in wine? Yeah I laughed

18:27

because there's another smell that people

18:29

always talk about that's interesting but

18:31

there are terpenoids. That's a petrel

18:33

smell in resling. And the petrosmelt

18:35

in reasoning, they are terpenoids. What's

18:37

interesting is that if you think

18:39

about it from a chemical perspective,

18:42

it's fascinating to connect to the

18:44

origins of them. So terpenoids are

18:46

actually not... complex chemicals. There are

18:48

just carbon units, right? We have

18:50

carbons everywhere. All the organic life,

18:52

they are carbon-based. So plants or

18:54

even some animals, they use carbons

18:57

to produce some aromas to attract

18:59

people or to make people think

19:01

they smell weird like recently or

19:03

petrelin recently. But if they're carbons,

19:05

right, they could be floral, but...

19:07

For the petrel smell in reasoning,

19:10

I can sort of see why

19:12

people connected to petrel because nowadays

19:15

people actually use terpenoids to make

19:17

biofuels. So if you think about

19:19

all carbon coming together, they are

19:22

petroleum, they are oils. It's just

19:24

with certain structure of the chemical

19:26

compounds, they could smell either like

19:29

petrel or all the way to

19:31

floral. Okay, so these turbanoids, they

19:34

vary. They're primarily coming from the

19:36

raw material, the grapes in this

19:38

sense, is that right? And also,

19:41

how do they vary beyond just

19:43

the raw material? How can they

19:46

vary, maybe in the same grape,

19:48

like resling, in different places? Yes,

19:50

so just pay attention to nature.

19:53

As soon as you get into

19:55

a garden or forest or anything,

19:57

just go outside. all sorts of

20:00

aromas, chances are, I dare say

20:02

50% of them that you can

20:05

smell floral, woody, or something like

20:07

that, they could be terpenoids. And

20:09

they vary, and sometimes they can

20:12

change as well. There are certain

20:14

compounds, like people try to find

20:17

out how they change, right? They

20:19

found out that certain floral terpenoids

20:21

can actually change to something minty

20:24

or more herbal. as wine ages

20:26

or a certain food like a

20:28

certain beverage product or cheese or

20:31

something ages. They just change in

20:33

their aroma nature. So therefore they

20:36

can change not just according to

20:38

where they are but according to

20:40

once they're in a bottle they

20:43

can evolve into other characters. Exactly

20:45

and that is why I personally

20:48

think those wines who are too

20:50

strongly floral or fruity at the

20:52

beginning they tend to have less

20:55

aging capacity. And those with those

20:57

kind of terpenoids or some other

20:59

compounds that's locked in the wine

21:02

that needs to age or needs

21:04

to breathe, they tend to have

21:07

longer aging capacity because they were

21:09

locked and reserved in the bottle

21:11

in the wine at the beginning

21:14

and later they slowly release. Okay,

21:16

so terpenoids cover a... big range

21:19

of aromas, including petrol in some

21:21

resling, which is a turponoid known

21:23

as TDN. And Gus writes in

21:26

his book that they permeate every

21:28

corner of nature and constitute a

21:30

powerful language in the form of

21:33

aromas. Different grape varieties have different

21:35

constituent turponoids which make them smell

21:38

different. And I understand from Gus's

21:40

book that even the same grape

21:42

variety will create different combinations of

21:45

turponoids due to environment... variations or

21:47

terroir. So that's really intriguing. Yeah,

21:50

yeah, so a chemical justification for

21:52

terroir and then all that can

21:54

then change in the bottle. As

21:57

Gus said, you know, for example,

21:59

the floral scented turponoid linole, I

22:01

think I hope I'm pronouncing that

22:04

right, which is often found in

22:06

Muscat, can be converted to one-eight

22:09

syniol over time, which smells more

22:11

like eucalyptus. So, you know, there's

22:13

more research to be done there,

22:16

but essentially, yes, you know, turponoids

22:18

are fascinating. They're about... Fruits using

22:21

volatile aromas to chemically signal their

22:23

maturity. So the concentration of beta

22:25

demacinone, which smells fruity and floral,

22:28

can be a marker for great

22:30

maturity, for example. But turponide smells

22:32

aren't just about floral and fruity.

22:35

They can also be spicy and

22:37

petrony. Yeah, absolutely. Intrigate. I think

22:40

a quick break and a breath,

22:42

and then we'll get back on

22:44

it. By way of

22:46

summary so far, wine chemistry

22:49

is complex, human perception too,

22:51

but we're starting to discover

22:53

intriguing things about both from

22:55

how simple carbon compounds can

22:57

make your sira smell of

22:59

pepper or your resling smell

23:01

of petrol to how your

23:03

perception of tannin can vary

23:05

according to your saliva flow.

23:07

I thought we'd agreed never

23:09

to talk about saliva again,

23:11

ever again. Anyway, okay, so

23:13

we've discussed terpenoids, but now

23:15

I wanted to hit Gus

23:17

with Ellen's original question, why

23:19

does Kavanaugh smell like black

23:21

current? So that's a different

23:23

group of compounds, and to

23:25

be honest, we don't know

23:27

the true nature yet of

23:29

the so-called black fruit, especially

23:31

black current. So far as

23:33

far as I can tell

23:35

from the literature, from the

23:37

scientific journals, a group of

23:39

major compounds that contribute into

23:41

the black current smell, they

23:43

are thiles or sulfides. Those

23:45

are sulfur related compounds, not

23:47

the sulfur as we do

23:49

when we add sulfur dioxide

23:51

into wine when we do

23:53

wine making, but those kind

23:55

of natural occurring solver compounds

23:57

either from the grape or

23:59

mostly coming from the fermentation

24:01

by the ease. It's a

24:03

byproduct of ease that tend

24:05

to generate those kind of

24:07

black fruit smell either in

24:09

cabinet Sauvignon or in certain

24:11

other red wines like sira

24:13

or those kind of drinks.

24:15

how much of the character,

24:17

let's say in a glass

24:19

of Kavanaugh's Sauvignon, is down

24:21

to the raw materials and

24:23

the grapes, and how much

24:25

is down to the winemaking,

24:27

the yeasts included in that

24:29

process. So if you ask

24:31

a winemaker, they tend to

24:33

tell you that most of

24:35

the aromas were coming from

24:37

fermentation or some other microbial

24:39

activities like malolactic conversion by

24:41

bacteria, right? That is true,

24:43

but... It's hard to say

24:45

in terms of if you

24:48

don't have certain things, what

24:50

we call the precursors existing

24:52

in the grapes in the

24:54

first place, the east will

24:56

not have the materials to

24:58

convert into the aromas later.

25:00

So I think it's hard

25:02

to say a percentage is

25:04

more helpful to think in

25:06

a way that they are

25:08

both very significant. The raw

25:10

materials as precursors of aromas

25:12

in the grape and how

25:14

the yeast bacteria later convert

25:16

those kind of raw materials

25:18

into aroma compounds. Okay, so

25:20

that's interesting because You'd maybe

25:22

assume that a black current

25:24

aroma from Cabernet sovignon would

25:26

be straightforward in terms of

25:28

the compound and pathway, but

25:30

it seems that's not the

25:32

case. You know, we're talking

25:34

precursor compounds and grapes that

25:36

are then converted by yeast

25:38

during fermentation into these volatile,

25:40

sulphur-containing compounds. You know, just

25:42

explains how we humans have

25:44

a... love hate relationship with

25:46

sulfides. You know, he cites

25:48

the example of the durian

25:50

fruit in his book, which

25:52

has failed with sulfides and

25:54

which some people adore and

25:56

others find absolutely unbearable revolting.

25:58

You know, we're all sensitive

26:00

to sulfides because they can

26:02

be dangerous. Hydrogen sulfide, which

26:04

smells of rotten eggs, can

26:06

be toxic in excess, which

26:08

is why... We fought to

26:10

get rid of it. You

26:12

did promise to get fasting

26:14

in here. I tell you

26:16

I was going to get

26:18

fasting. I don't always say

26:20

that. There we go. I

26:22

do try every episode. There

26:24

it is. But sometimes it's

26:26

only sometimes it's a very,

26:28

there we go. Told you,

26:30

sulphides are fascinating. Now apparently

26:32

decomposing bodies also release hydrogen

26:34

sulphide too. So again, it's

26:36

a smell we're wary of.

26:38

Our bodies do need sulphides

26:40

in small amounts, so we

26:42

learn to tolerate or even

26:44

like them. So coffee, for

26:46

example, is also full of

26:49

thiols or sulphides. And we

26:51

love coffee, so you know,

26:53

that love hate. dynamic there.

26:55

And in wine, just to

26:57

bring things back onto topic

26:59

here, we're talking smells like

27:01

black currant and cabine sovignon,

27:03

but also grapefruit in sovignon

27:05

blanc and then struck match

27:07

or fresh curry leaf in

27:09

what's often termed a flinty

27:11

or mineral or reductive style

27:13

of shardnae, for example. Yeah,

27:15

absolutely. So the former, the

27:17

the sovignon blanc, sulphide, is

27:19

three MH, and the latter

27:21

is benzene methane-methane thylthane thiol,

27:23

for what it's, for what

27:25

it's, for what it's... a

27:27

huge range of smells and

27:29

gas reckons. There are loads

27:31

we still haven't discovered yet,

27:33

which is intriguing. But we'll

27:35

come back to this subject

27:37

in a bit. Meantime, I

27:39

ask us, if precursors in

27:41

grapes are so important to

27:43

the wine's final taste, how

27:45

can you farm grapes to

27:47

generate the best possible raw

27:49

material for the wine? Yeah,

27:51

it all depends on the

27:53

winemaker's own experience and taste

27:55

and the growers experience because

27:57

there are just so many

27:59

things that's unpredictable during winemaking,

28:01

right? You don't know how

28:03

the ease will convert certain

28:05

precursors in the grape into

28:07

aromas. But there are some

28:09

markers that we can go

28:11

for and those markers tend

28:13

to be those on the

28:15

aroma compounds that already exist

28:17

in grape. and they are

28:19

readily to be released, such

28:21

as the turp noise, turpings

28:23

we talk about, such as

28:25

some other things like the

28:27

green bell pepper smell from

28:29

what we call the methoxy

28:31

purexins, right? They are there

28:33

because nature in grapes or

28:35

in other plants, in all

28:37

green parts of plants, they

28:39

produce those kind of green,

28:41

peppery, green aromas just to

28:43

repel those kind of... herbivores

28:45

or those kind of insects

28:47

that might damage and eat

28:50

the plant. So let's talk

28:52

about those mythoxy pyrosines for

28:54

a moment. You've talked about

28:56

these sort of green smells

28:58

that can maybe crop up

29:00

in grapes like Kavanaugh or

29:02

Sauvignon Blanc. How do they

29:04

get as if they're meant

29:06

to repel herbivores from eating

29:08

the leaves? How do they

29:10

get into the grapes and

29:12

the wine? So that's the

29:14

interesting part that... We don't

29:16

know why, but the truth

29:18

is that grapes like Cabernet

29:20

Sauvignon or the Cabernet family,

29:22

including Merleau, including especially Cabernetre,

29:24

they somehow can let the

29:26

piercings translocate or synthesize in

29:28

the grape skins. Or, should

29:30

I say, it remains in

29:32

the grape skins because most

29:34

of the grapes, as they

29:36

ripen, those piercings went away,

29:38

right? But those capering Sauvignon,

29:40

carbonary grapes, they keep those

29:42

kind of compounds in the

29:44

grape skin. But my personal

29:46

theory, this is not... exactly

29:48

100% scientific. My personal theory

29:50

is that Cabernet Sauvignon or

29:52

Sauvignon Blonde or Cabernetre, they

29:54

are, they tend to be

29:56

more ancient varieties and they

29:58

tend to have better capability.

30:00

potential of producing compounds that

30:03

help them survive in

30:05

the nature. If you think

30:07

about it, the more ancient

30:09

the grapes would be like

30:11

muscat, like Pinot Noir, they

30:13

tend to have more complex

30:15

aroma compounds and

30:17

that is probably

30:19

because throughout evolution

30:21

They generate this kind of

30:23

capability of producing either attractive

30:26

smells like those kind of

30:28

floral smell. Some people may

30:30

get in mascot Pinot Noir

30:32

or some disgusting smells

30:34

to insects, to herbivores, such

30:36

as methoxy piercing, those kind

30:39

of green nose, just to

30:41

help them survive better. But a

30:43

little bit of that green note can

30:45

actually work quite well in the wine.

30:47

You'd say sort of carbonate or carbonate

30:50

7. That could be really quite nice.

30:52

Exactly. That's why I personally would say

30:54

the Cabernet Sauvignon evolved in the way

30:56

that served human beings palette. So

30:58

the oldest grapes in evolutionary

31:00

terms are the ones with

31:02

the most complex aroma profile.

31:04

That's really interesting. I've never

31:06

even considered. Yeah, yeah, it's intriguing,

31:09

isn't I agree? But just to

31:11

go back to pyrosines, specifically, which

31:13

Gus mentioned, this is another

31:15

part of the Kavanaugh-Sovine aroma profile,

31:17

to go further into Ellen's question,

31:19

you know, that green pepper or

31:22

leafy or vegetable spectrum. And these

31:24

compounds are nitrogen-based and include things

31:26

like IBM, which smells like green

31:28

bell pepper and IP. which smells

31:30

like peas or potatoes fresh from

31:33

the earth. Now we had those

31:35

in our faults episode, didn't we? Our

31:37

wines false. And we discussed there. Yeah,

31:39

exactly, exactly. Yeah, exactly. And

31:41

we discussed there that some people

31:44

might find them objectionable, but for

31:46

others, in not too high a

31:48

concentration, they're fine. Exactly. So we've

31:50

touched on turbanoids, thals or sulphur-containing

31:52

compounds and pyrosines, but there's another

31:54

major group of aromas we need

31:57

to cover. I asked Gus to

31:59

give me... an example or two

32:01

of a wine style that's

32:03

influenced by the yeast from

32:06

wine making. So there are

32:08

two folds. One is that

32:10

for most of the fruity

32:12

smell we talk about turpone,

32:14

turpings, but there's another major

32:16

group of smell and those

32:19

are called esters. And esters

32:21

are... mostly fruity, such as

32:23

if you smell banana, banana

32:25

has lots of esters, right?

32:27

So those kinds of fruity

32:30

smell that can remind you

32:32

of certain fruit, they are

32:34

esters. And why they are

32:36

mostly made by the east? Because

32:38

esters were made by putting two

32:41

things together. One is a type

32:43

of acid, any acid. The other

32:45

is a type of alcohol. Okay,

32:48

so you put acid and

32:50

alcohol together, the east will

32:52

put them together, and then

32:54

you get a compound called

32:56

esters. And for most of

32:59

the flavoring industry nowadays, such

33:01

as the flavor or aromas

33:03

of soap or any type

33:05

of... food like yogurt, strawberry

33:07

flavoured yogurt or those kind

33:10

of things. They were all

33:12

made by adding esters that's

33:14

now synthesised by yeast or

33:16

just chemical engineering. So and

33:18

they are alcohols plus acid

33:20

so you need that fermentation

33:23

to be happening for them

33:25

to be produced in the first

33:27

place? Yes. So within the... body

33:29

of ease when they

33:31

metabolize during the fermentation,

33:34

they started to create

33:36

some intermediate alcohols and

33:38

acids and they tend to

33:40

put some of them together to

33:43

generate those kind of esters. Our

33:45

old friend Esther. She is.

33:47

Now we're talking fresh fruity

33:49

flavors with esters, right? I'm

33:51

thinking aromas like apple, pear,

33:53

peach, banana, strawberry, that kind

33:55

of thing, which are typically

33:57

found in young fruity wines.

34:00

like Bojole nouve, which people

34:02

often describe as tasting like

34:04

bananas or strawberry. Absolutely, you

34:06

know, as gas says, they're

34:08

made by yeast acting on

34:10

acids and alcohol. So isoamil

34:12

acetate is made from isoamil

34:14

alcohol and acetic acid and

34:17

it gives that... banana smell,

34:19

we're talking about. But over

34:21

time wine's acidic nature often

34:23

encourages esters to break back

34:25

down into their constituent parts,

34:27

a process called hydrolysis, meaning

34:29

these fruitie, these fresh fruitie

34:31

aromas can reduce in bottle,

34:34

make sense, right? Yeah. Older

34:36

wine smells less fresh and

34:38

fruity than those young young

34:40

ones. It's also a question

34:42

of balance, you know, for

34:44

example, ethar acetate in moderation

34:46

can smell just generically nicely

34:48

fruity. In excess, it's the

34:51

precise... combination of esters that

34:53

makes us think of certain

34:55

fruits not specific ester compounds.

34:57

What makes it more complicated

34:59

is that even with the

35:01

same concentration a certain ester

35:03

can give different aromas when

35:05

a liquid has a different

35:08

chemical makeup. So in short

35:10

it's hard to predict what

35:12

fruit aromas are wine is

35:14

going to have based just

35:16

on chemical data. It is

35:18

a symphony not a solo

35:20

act. Love that. symphony not

35:22

a solo act and all

35:25

orchestrated by our friends the

35:27

yeast. We should also remember

35:29

other ways in which those

35:31

wonderful microbes called yeast can

35:33

affect a wine's flavor. The

35:35

famous flavor of phenocheri is

35:37

largely down to the floor

35:39

yeast that sits on the

35:42

wine surface in the Salera

35:44

barrels. When it comes to

35:46

long-age traditional methods sparkling wine,

35:48

the dead yeast cells and

35:50

beaut the wine with flavor

35:52

and texture. And let's not

35:54

forget the sulphur-containing compounds we

35:56

touched on earlier called sulphides

35:59

or thiols. And I wanted

36:01

to use this as a

36:03

way to explore the idea

36:05

of sensorial or personal experience.

36:07

with gas. People really have

36:09

different sensitivities, especially towards sulphur-containing

36:11

compounds. Why? Because they could

36:14

be toxic. Because if you

36:16

smell too much of the

36:18

hydrogen sulfide, you will get

36:20

intoxicated. But we also need

36:22

them. We just need a

36:24

small percentage of them. Why?

36:26

Because those compounds can also

36:28

be compounds that help with

36:31

communication between cells. So within

36:33

our body. the sulfur-containing compounds

36:35

are actually messengers that help

36:37

communicate those kind of functions.

36:39

So it's a weird type

36:41

of compound that we may

36:43

hate it, but we may

36:45

also love it depending on

36:48

the concentration, also depending on

36:50

your own genetics. One example

36:52

I always say is if

36:54

people realize what a thing

36:56

called the asparagus pee or

36:58

coffee pee, they... will understand

37:00

this because after eating asparagus

37:02

and drinking coffee, as we

37:05

metabolize in our pea, in

37:07

our urine, we will have

37:09

those kind of compounds. But

37:11

some people, especially, I don't

37:13

know why, but it's probably

37:15

just genetic that in China,

37:17

when I asked students or

37:19

as a group of audience

37:22

about asparagus urine, and they

37:24

never they are never aware

37:26

of it. They never realized

37:28

that kind of smell. But

37:30

to most people I see

37:32

in UK and here where

37:34

I'm now in America, most

37:36

people can smell that, meaning

37:39

probably in certain populations like

37:41

in Caucasians versus Asians, Caucasians

37:43

have the genetics that that

37:45

are more sensitive to those

37:47

kind of smells. So we

37:49

vary in terms of genetics,

37:51

we vary in terms of

37:53

personal preferences, we also vary

37:56

between cultures when we can

37:58

all be assessing the same

38:00

wine, but we could be

38:02

tasting and smelling something completely

38:04

different. different, such as we

38:06

mentioned champagne or certain sparkling

38:08

wine, right? That's not necessarily

38:11

aromas, but when we put

38:13

those kind of traditional method

38:15

sparkling wines into in our

38:17

palate, okay, when we're actually

38:19

tasting the mouth, I tend

38:21

to find that it's harder

38:23

for me to explain what

38:25

is the umami taste. contributed

38:28

by the East Autoluses in

38:30

those kind of sparkling wines

38:32

towards at least American audiences.

38:34

Versus in China, if I

38:36

explain them to people, they

38:38

say, oh, of course I

38:40

can also taste that kind

38:42

of savory umaminess coming out

38:45

from the so-called East Autoluses.

38:47

That's really interesting. Can you,

38:49

well, since we're on the

38:51

subject, can you talk to

38:53

us a little bit about

38:55

the flavors, the chemistry in

38:57

a... traditional methods, maybe older

38:59

vintage sparkling wine like an

39:02

older champagne. Yes, so of

39:04

course there are certain fruity

39:06

smell as I mentioned coming

39:08

from the grape and also

39:10

those kind of esters fruitiness

39:12

coming from east. That's the

39:14

primary fermentation, right? But once

39:16

you get into the second

39:19

fermentation in the bottle and

39:21

you start to age the

39:23

wine with the least for

39:25

a long long time. they

39:27

start to release the most

39:29

complex compounds. They are dead

39:31

itself. They start to, why

39:33

is it called autolysis? Because

39:36

they start to automatically break

39:38

down from, they start to...

39:40

release all the things from

39:42

within their body. So what

39:44

you're essentially looking at is

39:46

that all sorts of compounds

39:48

from proteins, amino acids, to

39:50

all the unpredictable components that

39:53

scientists yet need to discover

39:55

more, and that is nothing

39:57

less complex than a glass

39:59

of milk because it's all

40:01

those... from the compounds that

40:03

are coming from an organic

40:05

life's body, the dead e-cells.

40:08

So yeast contributes flavor when

40:10

it's alive and also when

40:12

it's dead. They are heroic

40:14

little critters, aren't they? Why

40:16

heroes? And we do have

40:18

a lot to thank them

40:20

for in terms of flavor

40:22

chemistry or even just... deliciousness.

40:25

So much to be grateful

40:27

for. Now to finish off

40:29

I asked Gus about the

40:31

bigger picture. He took an

40:33

example from his own research

40:35

into TCA the the corktaint

40:37

compound which as we know

40:39

even in tiny amounts can

40:42

ruin even the most expensive

40:44

bottle of wine but he

40:46

then tested it out on

40:48

a different matrix. What I

40:50

also found interesting is that

40:52

those compounds in different drinks,

40:54

in different matrix, they tend

40:56

to have different sensory impacts.

40:59

For example, I used the

41:01

same group of people, including

41:03

myself, to smell the same

41:05

amount of TCA in a

41:07

wine versus in a glass

41:09

of whiskey. And in the

41:11

whiskey, they are not that

41:13

obvious. probably because the high

41:16

ethanol high alcohol content kind

41:18

of masked the TCA smell

41:20

in whiskey and it didn't

41:22

destroy much of the desirable

41:24

smells other aromas in whiskey

41:26

either so I found it

41:28

fascinating. Because you make the

41:30

point in the book about

41:33

other compounds in higher alcohol

41:35

drinks being actually much much

41:37

worse. Yes, so it really

41:39

depends on the matrix. So

41:41

what I try to tell

41:43

people in the book is

41:45

not only about the chemistry

41:47

side, it's also about we

41:50

should not just look at

41:52

a chemical compounds and think...

41:54

about the impact of this

41:56

compound on its own. It's

41:58

just a guidance that helps

42:00

her think, right? But it's

42:02

more of our job. or

42:04

our own mission to just

42:07

enjoy what it is in

42:09

a glass as a whole

42:11

complex matrix. Because the wine

42:13

is complex and we're complex.

42:15

Yes. How much do we

42:17

really understand about how the

42:19

interaction of this sort of

42:22

complex chemical suit results in

42:24

any given wine's character? Very

42:26

little, especially on the sensory

42:28

side. And that is why

42:30

my main research direction is

42:32

sensory studies. It's not about

42:34

I study one component and

42:36

I study certain genetics and

42:39

I can predict what will

42:41

happen. It's more about, hey,

42:43

there's a product over here.

42:45

whether it's a perfume or

42:47

it's a wine, and then

42:49

I see a group of

42:51

people or a large group

42:53

of people interacting with the

42:56

product and see their variability,

42:58

but also among those kind

43:00

of variability, can we see

43:02

some patterns that makes it

43:04

more commercially significant for the

43:06

winemaking world? Such as, again,

43:08

let's talk about Marlboros of

43:10

Nion Blanc. why it became

43:13

successful because they do have

43:15

that type of component in

43:17

the wine that can only

43:19

be made by modern winemaking

43:21

techniques such as certain ease

43:23

and anaerobic protective winemaking stainless

43:25

steel tank temperature control all

43:27

that and just hit the

43:30

sweet spot. of human beings.

43:32

So we need to just

43:34

test our product, not only

43:36

by machines, but also using

43:38

humans as machines, using human

43:40

nose, human palate to test

43:42

them. And that's what sensory

43:44

studies about, is that there's

43:47

nothing you can predict in

43:49

advance. AI can certainly not

43:51

not do that yet. It's

43:53

more about you have these

43:55

kind of recipe and you

43:57

let people. taste it and

43:59

test it and see if

44:01

they can make more sense

44:04

commercially. And companies like Coca-Cola,

44:06

Pepsi and all these kind

44:08

of companies, they do tons

44:10

of sensory studies just to

44:12

use human beings to verify.

44:14

Fascinating. So wine has an

44:16

sort of enchanting magic to

44:19

it of itself, but also

44:21

there's a profoundly human interaction

44:23

to make it all come

44:25

to life and make it

44:27

make sense. Exactly. Gus, thank

44:29

you very much indeed. Thank

44:31

you, Peter. So

44:36

it's reassuring to hear we humans still

44:38

have a part to play and I

44:41

like the idea that as much as

44:43

we try to simplify or reduce wine

44:45

to its chemical basics it still resists

44:47

easy categorisation and evaluation it's complicated we're

44:49

complicated and sometimes we should just enjoy

44:52

it for what it is. Yeah a

44:54

whole complex matrix as Gus says or

44:56

in other words a nice drink. We're

44:58

going to wrap things up there. Ellen,

45:00

I hope we've done your question some

45:03

sort of justice. I fear we've only

45:05

just scratched the surface of what is

45:07

a hugely... complex and intriguing realm. But

45:09

I'm sure we'll come back to this

45:11

topic from another angle in due course.

45:14

And in the meantime, for those who

45:16

want to know more, we'd recommend Gus's

45:18

book highly. On which note we have

45:20

a 15% discount code for you, which

45:23

apparently is currency agnostic. I do like

45:25

that motion. Which I can be currency

45:27

agnostic. So this code can work globally

45:29

and I think the publisher is shipped

45:31

to most places as well. The code

45:34

is Wine Blast 15 W-I-N-E-B-L-A-S-T-15. The book

45:36

is called Behind the Glass by Gussjou,

45:38

M-W. You can order it from Academy

45:40

Duvin Library.com and we definitely suggest you

45:42

do if you found this program has

45:45

peaked your interest and you want to

45:47

know a bit more. It's not expensive.

45:49

and it's fascinating stuff, really well written

45:51

and highly engaging. Yeah, there are bits

45:53

on tears, bubbles, legs, specific an osmear,

45:56

I mean I could go on. I

45:58

don't watch... I'm not sure... I think...

46:00

I'm not even sure... I'm not even

46:02

sure... I think that was me. I

46:05

think that was my only addition. And

46:07

it's all yours. It's a red flag,

46:09

isn't it? Oh dear, oh dear. Anyway,

46:11

there is all sorts of interesting stuff

46:13

in there for stuff in there that

46:16

we haven't in there that we hadn't

46:18

had, that we hadn't had time to

46:20

have, that we hadn't had time for

46:22

stuff in there, that we hadn't had

46:24

time for stuff in there, that we

46:27

hadn't had, that we hadn't had, that

46:29

we hadn't had, but, that we hadn't

46:31

had, that, that, that, that, that, but,

46:33

that, but, that, that, but, that, but,

46:35

that we hadn't, that, that, that, that,

46:38

but, he puts six contrasting pairs of

46:40

wines together to illustrate all his key

46:42

theoretical points in the book so you

46:44

can literally put all the theory into

46:47

practice just get these wines and taste

46:49

them it's really fun we definitely recommend

46:51

you do that because it really brings

46:53

it to life and you can call

46:55

it research which is how we justify

46:58

our entire career isn't it? So by

47:00

way of closing summary wine is one

47:02

of the most gloriously complex liquids on

47:04

the planet from a chemical perspective. It

47:06

has hundreds, if not thousands, of aromatic

47:09

compounds, from turponoids to sulfides, pyrosines to

47:11

esters and beyond. Its appearance and taste

47:13

and aging potential are all determined by

47:15

a complex string of chemical interactions, not

47:17

least of which is wine's interface with

47:20

us, tasters, whose human senses can be

47:22

just as complex as the wine. One

47:24

day we might understand every last chemical

47:26

nuance, but in the meantime we can

47:29

still enjoy the symphony without dissecting the

47:31

score. Ah, men to that. We didn't

47:33

get any explosions in the end, didn't

47:35

we? No. But hey, that's life. Maybe

47:37

next time, maybe next time. Our thanks

47:40

to Gus Ju and Academy Duvant library.

47:42

And of course, thanks also to you

47:44

for listening. Until next time. Cheers.