Winemaking and maturation

Question 1

What are the constituent parts of the grape ?

Answer 1

Seeds and stems
Skins
Bloom
Pulp

Question 2

What is the bloom of the grape ?

Answer 2

The waxy surface that contains the yeast.

Question 3

What is the most abundant acid in the grape pulp ?

Answer 3

1. Tartaric acid

2. Malic acid

Question 4

What is the most commonly used antioxidant ?

Answer 4

Sulfur dioxide

Question 5

What are the beneficial properties of SO2 ?

Answer 5

It is both an antiseptic (against unwanted strains of yeast and bacteria) and an antioxidant.

Question 6

What is the diference bewteen a barrique and a pièce ?

Answer 6

The barrique is of 225 litres and the pièce of 228.

Question 7

What is the difference between enrichment and chaptalization ?

Answer 7

Enrichment is carried out with RCGM, Rectified Concentrated Grape Must, where as chaptalization is carried out with suger from other sources than grapes, such as sugar beet.

Question 8

What temperature span does alcoholic fermentation take place in ?

Answer 8

Normally between 5 and 35 degrees.

Question 9

What are the advantages of fermentation at lower temperatures ?

Answer 9

Avoids the loss of the most volatile aromas (floral, often)

Can encourage the development of fruity flavours in white wines

Question 10

How can MLF be encouraged ?

Answer 10

By raising the temperature of the wine after the alcoholic fermentation and by not adding sulphur dioxide.

Question 11

What is the difference between the fine and the gross lees ?

Answer 11

The gross lees are particles of dead yeast cells and grape fragments that fall to the bottom of the fermentation of storage vessel within a few hours and can cause unpleasant aromas, if not removed.
The fine lees settle more slowly, throught the sine maturation process.
Some winemakers may choose to keep the white wine in contact with the fine lees during pre-bottling maturation.

Question 12

In order to benefit from medium to long-term ageing, what does a wine need to contain ?

Answer 12

Sufficient levels of tannin, acidity and/or alcohol, as well as flavours that will develop in an interesting way.

Question 13

What is free run juice ?

Answer 13

Crushing breaks the skins of grapes without breaking the seeds and liberates a quantity of juice known as free run juice.

Question 14

How is wine clarified ?

Answer 14

Sedimentation (can be accelerated by centrifugation)
Fining
Filtration

Question 15

What is racking ?

Answer 15

When the gross lees have settled, the wine is slowly and gently pumped into a different vessel (leaving the sediment behind) : may be repeated.

Question 16

What is fining ?

Answer 16

Addition of a fining agent that speeds up the clumping together of deposits that may else have clumped together in the bottle, and makes it possible to filter them away.

Question 17

When is wine filtered ?

Answer 17

After fermentation and during maturation, prior to bottling.

Question 18

What are the two main methods of filtration ?

Answer 18

Depth filtration (gross lees)
Surface filtration (usually after depth filtration).

Question 19

What is sterile filtration ?

Answer 19

If the surface filter is so fine it removes yeast and bacteria, this is referred to as sterile filtration.

Question 20

What 3 areas require stabilisation ?

Answer 20

Tartaric acid
Microbiology
Oxygen

Question 21

What are tartrates ?

Answer 21

Crystals of tartaric acid (as it is less soluble in wine than in grape juice).
White crystals in white wine or purple crystals in red wine.

Question 22

How can tartrates be avoided ?

Answer 22

Cool temperatures accelerate the formation of crystals, so if a wine undergoes a long maturation period in a cold cellar prior to bottling, it will deposit some of its tartrates during maturation.

Alternatively, the winemaker can chill the wine to below 0 degress for at short period, to force the crystals to form and then remove them by filtration.

Question 23

What types of wine are particularly at risk from yeast or bacterial spoilage ?

Answer 23

Wines that have not undergone MLF, low-medium alcohol wines, low acidity and a little residual sugar.
They must be handled very carefully, addition of SO2 as well as sterile filtration prior to packaging.

Question 24

What is microbiological stability and how is it achieved ?

Answer 24

All wines are at risk of microbiological contamination, even if the winery equipment is kept completely clean, except from fortified wines, as the high level of alcohol is toxic for any kind of microorganism.
Sterile filtration may reduce the risk of contamination. Therefore the wines that are particularly at risk of microbiological contamination, that is wines with low to medium alcohol, low acidity and a little residual sugar, are handled very carefully, added SO2 and sterile filtered.

Question 25

How may oxygen stability be obtained ?

Answer 25

• by avoiding exposure to oxygen, e.g. during packaging, by flushing the bottles with carbon dioxide or nitrogen before filling to eliminate oxygen
• by keeping SO2 levels topped up

Question 26

What are the advantages and disadvantages of glass bottles ?

Answer 26

Advantages - portable, cheap, strong, air proof, consumer preference and do not taint the wine’s flavours. The air proofness means that they are ideal for long-term storage and ageing (whereas air enters through plastic).

Disadvantages - heavy, rigid, weight adds to transport costs, and rigidity means that they cannot be packaged to make the best use of the available space.
Once open, there will be space for air, meaning vulnerability to oxidation.

Question 27

What are the advantages and disadvantages of closures made from cork ?

Answer 27

Advantages: it allows for slow oxidation, which many winemakers consider to give the optimal balance between primary and tertiary characteristics.

Disadvantages: cork taint (caused by a chemical called TCA, trichloroanisole) is a risk, oxidising is another risk that increases with the age of the wine, if the cork lets in too much air.

Question 28

What are the advantages and disadvantages of closures made from screw caps?

Answer 28

Advantages:

• they do not taint the flavours of the wine
• provide impermeable seal from air
• fruit flavours are preserved longer than with cork (therefore increasingly popular for wines with primary aromas)

disadvantages:

• it is still being debated wether the lack of oxygen transfer means that post-bottling maturation can not be done under screw cap. Screw caps allowing oxygen transfer are now being produced.
• consumer acceptance vary a lot

Question 29

Give three examples of post-bottling matured wines

Answer 29

Vintage port
The fines German Rieslings
cru classés Bordeaux

Question 30

What are the ideal conditions for post-bottling maturation ?

Answer 30

• undisturbed
• cold dark place
• constant temperature
• 10-15 degreed Celsius
• constant humidity
• bottles lying on their side to maintain cork moist and an optimum seal maintained