17. Specific Options for Producing Wines with Residual Sugar

Question 1

What are the four methods of concentrating grape must to produce a wine with residual sugar?

Answer 1

• Drying grapes on the vine
• Drying grapes off the vine
• Noble rot
• Freezing grapes on the vine

Question 2

Outline what happens to the grape in the over-ripening stage.

Answer 2

• The grape begins to shrivel.
• Water is lost by grape transpiration and sugars concentrate
• The flavours in the grape develop from ripe to very ripe flavours

Question 3

Give two examples of sweet wines that are made by drying grapes on the vine.

Answer 3

Vendages Tardives, Alsace
Spätlese, Germany and Austria

Question 4

What are the two methods of drying grapes on the vine in sweet wine production?

Answer 4

• Leaving the grapes on the vine
• Cutting the cane

Question 5

Outline the process of cutting the cane as an alternative to drying grapes on the vine.

Answer 5

• The cane of the vine is cut or broken off the vine a short time before harvest )the cane usually remains attached to the trellis at this point).
• The grapes shrivel more quickly than if the cane remained attached to the vine.
• This concentrates sugars, acids and flavours in the grapes and reduces hang-time
• Does not eliminate the risk of rot

Question 6

Name two regions where cutting the cane is used as a method for sweet wine production.

Answer 6

• Jurançon, France
• Australia (Eg Mount Horrocks ‘Cordon Cut’)

Question 7

Outline the process of drying grapes off the vine to concentrate sugars.

Answer 7

Grapes are harvested then dried either
* Outdoors; in the sun in warm climates, or;
* Indoors; in a temperature and humidity controlled room, which gives the ability to speed up the drying process and avoid the development of greay hot

Water evaporated during the drying process, concentrating the sugars, acids and flavours

Question 8

Give two examples of where drying grapes off the vine is used as a method to concentrate sugars.

Answer 8

• Recioto della Valpolicella
• Vin Santo

Question 9

What is the fungus responsible for grey and noble rot?

Answer 9

Botrytis Cinera

Question 10

Outline the onset of noble rot.

Answer 10

• Damp conditions in the morning allow the fungus botrytis cinera to develop on the grape.
• The fungus punctures the grapes’ skin with microscopic filaments, leaving tiny holes in the skin
• The warm, sunny afternoons slow the development of the rot and cause water to evaporate from the grape, concentrating sugars, acids and flavours
• The fungus can also modify some aroma compounds and generate its own unique flavours.

Question 11

What are the two conditions that make it noble rot more likely to develop?

Answer 11

• The grapes must be fully ripe before the development of the rot
• The grapes must be grown in a region that provides humid, misty mornings followed by dry, sunny afternoons.

Question 12

Give three examples of where noble rot is used to make sweet wines.

Answer 12

• Sauternes, France
• Beerenauslese and Trockenbeerenauslese, Germany & Austria
• Tokaji, Hungary

Question 13

What are the disadvantages of producing wines affected by noble rot?

Answer 13

• If conditions aren’t perfect, the rot may not develop favourably (grey rot when too damp) or not at all (when conditions are too dry).
• The spread of noble rot is never uniform, and requires skilled labour over a prolonged period of time to pick the affected grapes
• The selective picking and the fact water evaporates from the grapes mean that the volume of juice obtained is low, meaning low yields.
• Grapes infected by noble rot are difficult to process in the winery

Overall, the production of noble rot wines is difficult and expensive

Question 14

Why are grapes infected by noble rot difficult to process in the winery?

Answer 14

• The fungus contributes an enzyme (called laccase) that is capable of oxidising a number of components in grape must and wine, and is relatively resistant to SO2.
• The thick, high-sugar-content must is difficult to press, clarify and ferment.

Question 15

What is the enzyme contributed by botrytis cinera that causes oxidation of the must?

Answer 15

Laccase

Question 16

How can a winemaker minimise the oxidation of must caused by laccase?

In the production of noble rot affected wines.

Answer 16

Chilling, high doses of SO2 and use of inert gases.

Question 17

What vessels are typically used for the maturation of wines affected by noble rot?

Answer 17

• Oak if a neutral grape variety (such as Semillon) is used, and where a broader texture and addition of oak flavours are desired
• Stainless steel or concrete if an aromatic grape varieties to retain their more pronounced varietal aromas.

Question 18

Outline the process of freezing grapes on the vine.

Answer 18

• Healthy grapes are left to hang on the vine into the late Autumn or winter months
• When freezing temperatures arrive, the water in the grape pulp turns to ice.
• When the grapes are picked and pressed, this ice remains in the press and the sugar content of the resulting juice is concentrated.

Question 19

Where is Ice Wine produced?

Answer 19

Most noteably Germany (where it is known as Eiswein), and Canada.

But ice wine is also produced in other parts of Europe as well as USA and China among others.

Question 20

What are the two most popular grapes used for ice wine production?

Answer 20

Riesling and Vidal

Question 21

What are the essential vine properties for ice wine production?

Answer 21

The vines used for these stylesof wine need to be winter hardy and have grapes with resilient skins that can offer protection from disease and can withstand the strain of freeze–thaw cycles.

Question 22

What are the typical fermentation and maturation practices for ice wines?

Answer 22

Ice wines are typically fermented and stored in stainless steel to retain the primary aromas and flavours of the grape variety. Oak maturation is sometimes used to add extra flavours.

Question 23

What is cyroextraction?

Answer 23

An alternative for freezing grapes on the vine in sweet wine production.
Grapes are picked in the autumn (at the same time as those for dry wines) and then frozem at a winery

Question 24

What is an alternative to freezing grapes on the vine?

Answer 24

Cyroextraction

Grapes are picked in the Autumn and frozen at the winery.

Question 25

What are the advantages of cyroextraction?

Answer 25

• Can be used by winemakers in regions that would not get the typical climatic conditions required for Eiswein and Icewine.
• It also does not entail the risks of leaving the grapes on the vine into late autumn or winter and perhaps losing yield to disease or pests
• Cheaper than the traditional ice wine production

Question 26

What is the main disadvantage of cyroextraction?

Answer 26

It is not permitted in the production of Eiswein and Icewine and therefore wines made by cryoextraction cannot use these terms on the label.

Question 27

What are the advantages of producing wines with residual sugar by stopping fermentation?

Answer 27

• The winemaker has control over the level of sugar in the final wine. The earlier the fermentation is halted, the higher the level of residual sugar that will remain (but also the lower the level of alcohol).
• The process is relatively quick, simple and low risk and so it is often used to produce wines that are inexpensive or mid-priced.

Question 28

How is fermentation stopped to retain residual sugar?

Answer 28

• The wine is chilled to below 10°C and/or adding a high dose of SO2 to inhibit the yeast. The wine is then racked off its sediment and sterile filtered to ensure fermentation does not start again at a later stage.
• Fortification, the addition of alcohol to kill the yeast, is also an option.

Question 29

What are the advantages of adding a sweetening component when making wines with residual sugar?

Answer 29

• Wines can be stored until ready for bottling, then the sweetening component can be blended in; dry wines are less susceptible to spoilage organisms than wines with residual sugar.
• The winemaker is also able to trial, measure and add the amount of sweetener, allows a high level of control, enabling high volumes of a consistent product to be made.
• Adding a sweetening component will maintain or possibly slightly increase the volume of the final wine

Question 30

What are the three most common sweetening agents used to produce wines with residual sugar?

Answer 30

• Sugar
• Rectified Concentrated Grape Must (RCGM)
• Unfermented grape juice (Süssreserve)

Question 31

What are the benefits of using RCGM as a sweetening agent for wine?

Answer 31

RCGM is processed so that it just contains the sugar from the grape. It is therefore neutral, and smaller amounts are required to sweeten the wine.