D1: Wine components

Question 1

Wine is made up of a complex array of compounds, some which have come directly from the grapes and others which have been formed during the fermentaion process. What are the main groups of compounds ?

Answer 1

1) Water
2) Alcohol
3) Acids
4) Wine aromatics:
- - aromas from the grapes
- - “ created by ferm due the presence of aroma percursors in grape must
- - “ originating from fermentation and its by-products
- - “ from orher sources
5) residual sugar
6) Glycerol
7) Phenolics

Question 2

Water:

Answer 2

Water is approximately 85% water by volume on the depending on the abv, level of residual sugar and other factors
– water is critical for the way a wine flows as a liquid

Question 3

Alcohol:

Answer 3

Ethanol is formed during fermentation and is the predominant alcohol in wine.

• • slightly sweet smell
• • contributes to the sense of sweetness and bitterness and oral warmth
• • also a contribution to the fullness of the body and the mouthfeel
• high alc levels 14,5 and above reduce the:
• volatility of wine aromas
• – increase the sense of bitterness
• • wines with these high alc needs sufficient fruit concentration to be in balance with the alcohol

Question 4

The principal acids in wine are:

Answer 4

tartaric and malic acids

• these come from the grape itself
• • studies have shown that these two make up about 2/3 of the total acidity in wine

Other acids (eg lactic acid, acetic acid) are produced in fermentation

Question 5

What is volatie acidity ?

Answer 5

1) refers to acetic acid (vinegar smell)
- - although some other compounds can contribute
2) it is present in all wines
- - and is only a fault when in excess
3) acetic acid in turn reacts with the alcohol in the wine and becomes ethyl acetate (nail varnish remover smell)
- – also perceived as a fault when in excess

Question 6

How do acidity contributes to the structure of the wine?

Answer 6

1) makes wine refreshiing and should be in balance with the furit concentration and, if present residual sugar

2) high acid also make wine appear leaner on the palate
3) excessive acid will make the wine taste tart
4) lack of acid will make the wine taste flabby

Question 7

The perception of acidity and of dryness is related not just to the level of acidity, but

Answer 7

the balance of acidity and any residual sugar

eg some german rieslings taste dry but have up to 9g/l residual sugar

Question 8

The levels of individual acids can also affect the tast of wine ex.

Answer 8

high levels of malic acid will give the wine a firm acidity

eg chardonnay from cool climates where the malolactic ferm was blocked

Question 9

In wine total acidity and Ph is linked but not correlated (samenhangend)

Answer 9

This is due the buffering (tegengaand) effect of other molecules like Potassium

A wine with high acidity would usually have a low ph and vica versa

Question 10

acidity can be measured and expressed in several ways, but the most common measure is total acidity (sum of all the acids)

Answer 10

oke

Question 11

Although there are many acids present:

Answer 11

The result will usually be expressed as the equivalent of grams/ l in tartaric acids

Question 12

total acidity in wine is typically in the range of:

Answer 12

5.5-8.5 g/l

Question 13

In france the total acidity may be expressed as sulfuric acid

Answer 13

The ratio between sulfuric and tartaric acid is 1:1.5

Question 14

What if the total acidity is measured in g/l ?

Answer 14

pH is a scale of measureent for the concentration of the effective acidity of a solution

Wines typically have a pH in the range of 3-4

• • this is an inverse scale
• – so the lower the number, the more concentrated the acidity (and the sharper a wine will taste)

The scale is lagorithmic, so:
PH of 3 is ten times more acidic than a ph of 4

Question 15

pH levels affects a range of key parameters in winemaking:

Answer 15

1) a low ph increases the microbiological stability of wine
2) increases the effectiveness of so2
3) gives red wines a bright red colour
4) enhances a wines ability to age well

Question 16

Wine contains many aromatic and non aromatic compounds. it aromatic complexity arises from the presence of these molecules and from their interaction with each other The compounds come from four sources:

Answer 16

1) aromas from the grapes
2) aromas created by fermentation due the presence of aroma precursors in grape must
3) aromas originating from fermentation and its by products
4) aromas from other sources

Question 17

Aromas from the grapes:

Answer 17

1) methoxypyrazines occur in the SB variety and give a grassy, green pepper aroma
2) rotundune occurs in syrah and in gruner velt, producing a pepper aroma

Question 18

Aromas create by fermentation due to the presence of aroma percursors in grape must:

Answer 18

Aroma precurcors are compounds that are not in themselves aromatic but are building blocks which become aromatic during fermentation.
for example:

many compounds occurs in grapes in a form combined with sugar as aroma less precursors

—- however through the precess of fermentation they become aromatic

1) Thiols are a category of aromatic compounds that are released during fermentation (example is 4MMP which gives the box tree aromas in SB

2) Terpenes is another category of compounds formed in this way
- - theyre widely found in wines, giving fruity and floral aromas
- — examples includes Linalool and geraniol contribute to the grapey aroma/ flavours in muscat

Question 19

Aromas originating from fermentation and its by products: Some aromas do not originate from the grapes but are created from fermentation and its by products such as lees:

Answer 19

1) esters are compounds which are formed by the reaction of certain acids and alcohols
- - the majoity are created through the action of yeasts in the fermentation process
- - esters are responsible for many fresh and fruity aromas and therefore essential in the aroma profile of young wines
- — the most important is isoamyl acetate, which gives aromas of banan when its concentration is high (beaujolais nouveau) but others produce apple, pineapple and many other aromas
- — an other important is ethyl acetate
* most esters are unstable and will brake down a few months after fermentation

2) acetaldehyde occurs in wines due to the oxidation of ethanol. also kwown as ethanal
- - it masks fresh fruit aromas and has a stale smell that is regarded as a fault in most wines
- – however it is an important component of the distinctive smell of fino sherry

3) Diacetyl is produced during fermentation and especially malolactic conversion. it contributes a buttery aroma

4) in certain conditions,yeast can produce reductive sulfur compounds during fermentation and lees ageing;.
Depending on the types of compounds present in the wine and their levels of concentration, aromas can range from:
- struck match (stekskes) which may be desirable
— rotten eggs which would be regarded as a fault

Question 20

There are numerous other sources of aromas found in different wines for example:

Answer 20

1) vanilin, which gives aromas of vanilla, is just one of the aromatic compounds that can be derived by ageing wines in new oak barrels
2) eucalyptol, which can be volatized from eucalyptus trees by heat and absorbed in the waxy layer of the skins of grapes in nearby vines, may be detected in wine

Question 21

Residual sugar:

Answer 21

1) Dry wines usually have a small amount of RS (2-3g/l)
2) off dry: sauternes 150g/l, pedro ximenez up to 400g/L
3) also gives more body to the wines

Question 22

What about the EU classification of sweetness level ?

Answer 22

The EU has 2 classifications of sweetness levels in wine: one for sparkling and one for still wines:

Still: The classification takes into account 2 factors:

• level of residual sugar
• optionally higher level of residual sugar for wine with higher total acidity
• — in an attempt to guide consumer as to the taste of the final wine

1) Dry/ sec/ trocken, etc: up to 4g/L rs, or not exceeding 9g/l rs if the total acidity (expressed in tartaric acid) is not more than 2 g below RS content
eg: a wine with 9G/l rs can be labelled sec if it has 7g/l total acidity

2) medium dry/ demi sec halbtrocken, …: more than 4g/l rs and not more than 12g/l, or up to 18 g/l provided that the total acidity expressed as grams of tartaric acids per litre is not more than 10g below the rs content
3) medium or medium sweet/ moelleux/ lieblich etc: more than 12g/l and not exceeding 45 g / l
4) sweet/ doux/ süss etc: at least 45 g / rs

Question 23

What about glycerol ?

Answer 23

1) glycerol is the most abundant part of the wine after water and alcohol (in dry wines) and is derived from the sugar in the grapes
2) it occurs in higher levels in wines made from botrytis affected grapes (eg tokaji) and wines made by carbonic maceration (eg beaujolais nouveau) although to a lesser extent than those made from botrytis affected grapes
3) glyceros contributes smoothness to the texture of wine and the perception of the fullness of the body
- - it has a slightly sweet taste

Question 24

Phenolics:

Answer 24

1) phenolics refers to an important group of compounds that occurs in grapes, especially in the skins, stems and seeds
2) they include both anthocyanins (colour pigments responsible for the red colour and sometimes blue tints of red and rosé wines) and tannins

3) in broad terms:
- - tannins bind with proteins in the mouth, giving a dry sensation of the palate
- — however the exact relation between the tannin compounds of the grapes, tannin compounds in the wine and the sensation of tannins in the wine is very complex and not well understood

• • it is thought that the perception of tannins can be influenced by the other compounds in the wine:
• a Little RS can make the tannins seem softer
• dry wines with high acidity can make tannins appear more astringent

4) tannins can also react with other compounds in wine during winemaking and maturation, changing their composition and hence how they are perceived
- - unripe tannins general taste bitter and are never desirable
- - the level and nature of the tannins and their role in the balance and structure of a wine as a whole is considered a key part of quality in red wines