Winemaking Chemistry

Question 1

what does the flesh of grapes contain?

Answer 1

h2o
Acids (malic - hard acid green apple, tartaric, citric - small amounts)
sugars (fructose, glucose and others)

Question 2

what are in the skins of grapes?
white
red

Answer 2

red: anthocyanins - red-brown colour in nature
white: carotenoid, varies from water white to yellow gold

Question 3

what are the requirements for an alcoholic solution?

Answer 3

• complex carbs (sugars)
• aqueous solution: h20
• ambient temp approx 18-22
• a vessel
• yeast (not any yeast, most common is Saccharomyces cerevisiae)

Question 4

what is ethanol?

Answer 4

alcohol that can be metabolised by the healthy adult human liver

Question 5

reds are typically higher in alcohol than whites, by what percentage?

Answer 5

23% higher

Question 6

what is the alcohol percentage of most wines?

Answer 6

12-15%

Question 7

when is residual sugar created?

Answer 7

when ferment stops before Dryness (before all sugars are consumed by yeast)

Question 8

what are the by-products of alcoholic fermentation?

Answer 8

heat 
CO2 
aroma and flavour compounds... include: 
- acetic acid and acetaldehyde (vinegar-like) 
- hydrogen sulphide (natural gas) 
- glycerol, adds to the mouthfeel 
- volatile esters, essential flavour compounds 
- lees - dead yeast cells

Question 9

are there different strands of Saccharomyces cerevisiae?

if so give examples

Answer 9

Yes
S. bayanus
S. beticus

Question 10

what are the two things that influence how much sugar is in wine?

Answer 10

how much sugar there is and how vigorous the yeast are

Question 11

in the last 20 years, what percentage of alcohol in wine has it gone up?
why is this

Answer 11

1. 5%

- getting warmer and the yeast that have been cultured are getting stronger/more effective at doing their job

Question 12

which is a drier white wine?

riesling or chard?

Answer 12

riesling

Question 13

a very dry wine doesn’t exist, what is the consumer actually asking for?

Answer 13

white: high acidity in the wine
red: high tannins in the wine

Question 14

regarding dry wine, what are the only two ways wine can turn out?

Answer 14

either a dry wine (no fermentable/residual sugar)

or there is some amount of residual sugar so degrees of sweetness

Question 15

if there is residual sugar, how do we ensure there is no more fermentation in the bottle?

Answer 15

• super chill the wine so the yeast cannot operate

Question 16

how can we control the heat in the ferment?

Answer 16

open the cap - aeration

- put refrigeration ferments in

Question 17

what makes up sediment?

Answer 17

crystalline tartaric acid

lees - dead yeast cells

Question 18

what happens in malolactic fermentation?

Answer 18

lactobacillus converts malic to lactic acid

Question 19

when does MLF usually occur?

Answer 19

it is done in almost all red wines, and some whites… usually takes place in barrel

Question 20

why do we do MLF?

Answer 20

for stability, so there is no build-up of CO2 in the bottle which could cause it to explode
also can give buttery/creamy lactic taste

Question 21

what is stability when referring to additives in wine?

Answer 21

ensuring that the products is what the consumer expects and improving shelf life to ensure that it remains that way… also involved preventing against microbiological spoilage

Question 22

what are the two most common additives that are allowed to be in the wine bottle at the end of the day?

Answer 22

sulphur dioxide - SO2

acid (tartaric and ascorbic)

Question 23

how much sulphur dioxide did we add to our ferment?

Answer 23

30 parts per million

Question 24

what is the diff. between free and bound SO2

Answer 24

the free so2 is the one doing its job as an anti-microbial

Question 25

what happens to SO2 in a barrel/bottle over time?

Answer 25

it will bind to the wine, so the bound total will go up, and there will be less free SO2 acting as an antimicrobial

Question 26

why might tartaric acid be added to wine?

Answer 26

for ph stability - to lower pH... and also for taste and flavour makes the fruit taste a little bit fresher, overripe, more jammy and lift the fruit flavours of the wine if grapes are coming from a hot region, more likely to have higher TSS which means you will need to add acid to lower ph

Question 27

when we refer to adding acid, what measurement do we use?

Answer 27

in grams per litre | 1-2 is okay or standard, while 5-6 is generally considered as a lot

Question 28

ascorbic acid is primarily added to whites, why?

Answer 28

for the freshness of palate and stop browning

Question 29

what are you trying to achieve with clarification

Answer 29

that the wine in the glass is clear | in red - to enhance the vibrancy of colour

Question 30

how can we clarify/fine?

Answer 30

the biggest one is gravity... sediment etc will sink to the bottom

Question 31

what is fining?

Answer 31

based on the assumption that some of the compounds that create haziness/cloudiness can be bound together and when they become large enough, can be removed

Question 32

in addition to gravity, how can we accelerate clarification/fining?

Answer 32

``` egg whites (albumen) milk products isinglass - dried swim bladders of fish gelatin casein, the potassium salt of casein ```

Question 33

t or F, additives are not allowed to give flavour profiles?

Answer 33

True