Winemaking Chemistry Flashcards
what does the flesh of grapes contain?
h2o
Acids (malic - hard acid green apple, tartaric, citric - small amounts)
sugars (fructose, glucose and others)
what are in the skins of grapes?
white
red
red: anthocyanins - red-brown colour in nature
white: carotenoid, varies from water white to yellow gold
what are the requirements for an alcoholic solution?
- complex carbs (sugars)
- aqueous solution: h20
- ambient temp approx 18-22
- a vessel
- yeast (not any yeast, most common is Saccharomyces cerevisiae)
what is ethanol?
alcohol that can be metabolised by the healthy adult human liver
reds are typically higher in alcohol than whites, by what percentage?
23% higher
what is the alcohol percentage of most wines?
12-15%
when is residual sugar created?
when ferment stops before Dryness (before all sugars are consumed by yeast)
what are the by-products of alcoholic fermentation?
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
are there different strands of Saccharomyces cerevisiae?
if so give examples
Yes
S. bayanus
S. beticus
what are the two things that influence how much sugar is in wine?
how much sugar there is and how vigorous the yeast are
in the last 20 years, what percentage of alcohol in wine has it gone up?
why is this
- 5%
- getting warmer and the yeast that have been cultured are getting stronger/more effective at doing their job
which is a drier white wine?
riesling or chard?
riesling
a very dry wine doesn’t exist, what is the consumer actually asking for?
white: high acidity in the wine
red: high tannins in the wine
regarding dry wine, what are the only two ways wine can turn out?
either a dry wine (no fermentable/residual sugar)
or there is some amount of residual sugar so degrees of sweetness
if there is residual sugar, how do we ensure there is no more fermentation in the bottle?
- super chill the wine so the yeast cannot operate
how can we control the heat in the ferment?
open the cap - aeration
- put refrigeration ferments in
what makes up sediment?
crystalline tartaric acid
lees - dead yeast cells
what happens in malolactic fermentation?
lactobacillus converts malic to lactic acid
when does MLF usually occur?
it is done in almost all red wines, and some whites… usually takes place in barrel
why do we do MLF?
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
what is stability when referring to additives in wine?
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
what are the two most common additives that are allowed to be in the wine bottle at the end of the day?
sulphur dioxide - SO2
acid (tartaric and ascorbic)
how much sulphur dioxide did we add to our ferment?
30 parts per million
what is the diff. between free and bound SO2
the free so2 is the one doing its job as an anti-microbial
what happens to SO2 in a barrel/bottle over time?
it will bind to the wine, so the bound total will go up, and there will be less free SO2 acting as an antimicrobial
why might tartaric acid be added to wine?
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
when we refer to adding acid, what measurement do we use?
in grams per litre
1-2 is okay or standard, while 5-6 is generally considered as a lot
ascorbic acid is primarily added to whites, why?
for the freshness of palate and stop browning
what are you trying to achieve with clarification
that the wine in the glass is clear
in red - to enhance the vibrancy of colour
how can we clarify/fine?
the biggest one is gravity… sediment etc will sink to the bottom
what is fining?
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
in addition to gravity, how can we accelerate clarification/fining?
egg whites (albumen) milk products isinglass - dried swim bladders of fish gelatin casein, the potassium salt of casein
t or F, additives are not allowed to give flavour profiles?
True
