Winemaking Chemistry Flashcards

1
Q

what does the flesh of grapes contain?

A

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

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2
Q

what are in the skins of grapes?
white
red

A

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

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3
Q

what are the requirements for an alcoholic solution?

A
  • complex carbs (sugars)
  • aqueous solution: h20
  • ambient temp approx 18-22
  • a vessel
  • yeast (not any yeast, most common is Saccharomyces cerevisiae)
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4
Q

what is ethanol?

A

alcohol that can be metabolised by the healthy adult human liver

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5
Q

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

A

23% higher

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6
Q

what is the alcohol percentage of most wines?

A

12-15%

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7
Q

when is residual sugar created?

A

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

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8
Q

what are the by-products of alcoholic fermentation?

A
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
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9
Q

are there different strands of Saccharomyces cerevisiae?

if so give examples

A

Yes
S. bayanus
S. beticus

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10
Q

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

A

how much sugar there is and how vigorous the yeast are

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11
Q

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

A
  1. 5%

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

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12
Q

which is a drier white wine?

riesling or chard?

A

riesling

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13
Q

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

A

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

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14
Q

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

A

either a dry wine (no fermentable/residual sugar)

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

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15
Q

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

A
  • super chill the wine so the yeast cannot operate
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16
Q

how can we control the heat in the ferment?

A

open the cap - aeration

- put refrigeration ferments in

17
Q

what makes up sediment?

A

crystalline tartaric acid

lees - dead yeast cells

18
Q

what happens in malolactic fermentation?

A

lactobacillus converts malic to lactic acid

19
Q

when does MLF usually occur?

A

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

20
Q

why do we do MLF?

A

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

21
Q

what is stability when referring to additives in wine?

A

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

22
Q

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

A

sulphur dioxide - SO2

acid (tartaric and ascorbic)

23
Q

how much sulphur dioxide did we add to our ferment?

A

30 parts per million

24
Q

what is the diff. between free and bound SO2

A

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

25
Q

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

A

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

26
Q

why might tartaric acid be added to wine?

A

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

27
Q

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

A

in grams per litre

1-2 is okay or standard, while 5-6 is generally considered as a lot

28
Q

ascorbic acid is primarily added to whites, why?

A

for the freshness of palate and stop browning

29
Q

what are you trying to achieve with clarification

A

that the wine in the glass is clear

in red - to enhance the vibrancy of colour

30
Q

how can we clarify/fine?

A

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

31
Q

what is fining?

A

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

32
Q

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

A
egg whites (albumen) 
milk products 
isinglass - dried swim bladders of fish 
gelatin 
casein, the potassium salt of casein
33
Q

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

A

True