Winemaking Flashcards
Explain the measures winemakers take to prevent oxygen to ruin wine with primary fruit characteristics.
How is this style of winemaking referred to?
Grapes are picked at night when the temperatures are lower and chemical reactions (oxidation) go slower. In the winery, tanks are filled with carbon dioxide or nitrogen before grape processing or wine making occurs in these. Sulfur dioxide is used as it is an effective anti-oxidant.
This is called protective or anaerobic winemaking.
Describe the effect of aerobic maturation on the flavors of a wine.
Aerobic maturation happens in wooden vessels that are watertight but not airtight. Small amounts of oxygen enter and react with the wine, reducing primary fruit flavors and developing tertiary characters such as leather and earth. More complex flavors and it also leads to softer tannins.
What aspect of barrel fermentation causes additional tertiary flavors to develop in maturing wine (often used with Rutherglen Muscat, Tawny Port, and Oloroso Sherry)?
Not only the effect of oxygen entering the oak barrel, but also filling up the containers for less than 100%. This causes additional surface exposure of wine to oxygen.
What are the two uses and effects of sulfur dioxide in winemaking?
- Antioxidant: SO2 protects the grape juice or wine from oxidation: this way it becomes bound
- Antiseptic: SO2 is toxic to yeasts and bacteria
What are the flavors coming from oak in wine?
Toast, vanilla, smoke, and cloves (Dutch: “kruidnagel”)
Describe the crushing process of grapes.
Crushing breaks the skins of grapes and liberates a quantity of juice (“free run juice”). Crushing should not damage the seeds.
What are fractions?
Separating the liquids from various degrees of pressing.
Describe the process of enrichment.
Enrichment is adding Rectified Concentrated Grape Must (RCGM) before or during fermentation to the juice. This increases the sugar level in the juice, hence also the alcohol level of the final wine.
What is the difference between chaptalization and enrichment?
It is both adding sugar to the unfermented juice or must, however, for chaptalization sugar comes from other sources than grapes (for enrichment RCGM = Rectified Concentrated Grape Must is used).
Describe the process of fermentation.
This is the conversion of sugar into alcohol and CO2 through the action of yeasts (mostly Saccharomyces cerevisiae). Other by-products are heat and flavor compounds.
What are the effects of the fermentation temperature on flavors in the wine?
Fermenting at lower temperatures avoids the loss of volatile aromas (floral aromas). It also encourages the development of fruity flavors.
Fermenting at higher temperatures leads to more extraction of color and tannins from black grapes
Describe the malolactic fermentation.
Lactic acid bacteria convert the malic acid (also found in apples. Dutch: “appelzuur”) into lactic acid (also found in milk). It softens acidity, creates buttery flavors and produces CO2. Raising the temperature encourages MLF, not adding SO2 has the same effect.
A winemaker can choose to avoid the MLF by use of SO2, storage at cool temperatures, and by filtering out the lactic acid bacteria that start the process.
What are the gross lees?
The dead yeast cells and grape fragments that remain after fermentation, and fall to the bottom of the fermentation vessel themselves.
What are the fine lees?
Sediments that remain after fermentation in the vessel. These are removed gradually later in the winemaking process. The fine lees give extra flavors and a richer texture to the (white) wine.
Why do some inexpensive as well as expensive wines benefit from a short pre-bottling maturation?
When the winemaker wants to retain as many fruity flavors (or the wines don’t benefit from further maturation in oak or in presence of oxygen), the wine is kept in inert tanks until bottling a few months after fermentation.
What are the three main reasons for blending wines after fermentation or during maturation?
- Adjust balance - Enhance the quality, for example, adjust tannin by blending free run wine with press wine
- Improve consistency - Rule out variations in the bottled product when grapes come from different vineyards or wine has matured in different oak barrels.
- Choose a style - Blending using different press fractions, fermenting or maturing in different vessels, or only part of wine going through MLF
What are the three methods or clarification of a wine before bottling?
- Sedimentation - by force of gravity the sediment is slowly pulled to the bottom of the vessel. Gently pumping over the wine to separate it from the sediment is called ‘racking’.
- Fining - Speeding up the clumping together of some wine constituents by a fining agent (the lumps that form can be removed by filtering)
- Filtration - Removing particles by passing the wine through a filter (quickly removes gross and fine lees)
Describe the two filtration methods of a wine.
- Depth filtration - wine passes through a thick layer, solid parts become trapped (good for removing gross lees)
- Surface filtration - removes finer particles by passing wine through fine sieves; the particles clog upon the surface of the filter. Sterile filtration is the removal of yeast and bacteria that are still present.
What are tartrates?
Crystals of tartaric acid, which is less soluble in wine than in grape juice. Cool temperatures accelerate the formation of these crystals that can be filtered out later.
What sort of wines are not easily affected by microorganisms?
Dry, high-acid wines that have undergone MLF, or high-alcohol wines such as fortified wines.
Most easily affected are wines that did not undergo MLF, and low-alcohol and low-acidity wines. These undergo sterile filtering prior to packaging.
What are the biggest risks to the stability of a bottled wine?
Tartrates that are formed (especially at low temperatures), attack by microorganisms such as yeasts and bacteria (in certain types of wine), and oxygen.
What causes cork taint in a wine?
A chemical called TCA = trichloroanisole, which is present in some corks.
What differentiates regular cork from screw caps?
Screw caps completely seal the wine preventing any oxygen to come in, preserving fruit flavors. Cork lets some oxygen through gradually, allowing tertiary flavors to develop.
Describe the ideal conditions for post-bottling maturation.
Store the wine undisturbed in a cool, dark place between 10 and 15 degrees. Constant humidity and the corks should remain moist (bottles lay down on the side).
In contrast to most white winemaking, for certain aromatic varieties, the juice is in contact with the skins before being sent to the press. Why?
For aromatic varieties, you want maximum extraction to increase flavor intensity and texture. This lasts for a few hours and is done at low temperature to inhibit an early start of fermentation.
What is the optimum temperature for white wine fermentation?
What is the effect of too high or too low fermentation temperatures?
Fermentation temperature: 12 to 22 degrees
Too low temperature: pear drop aromas and not enough varietal fruit character
Too high temperature: complex aromas but the loss of varietal fruit characteristics
What are the three main choices a winemaker needs to make post-fermentation?
- Mature in oak or store in inert vessels with or without wood staves/chips
- Use fine lees to add texture and flavor
- Allow or block MLF
Why is MLF usually avoided for premium, highly aromatic wines?
The high levels of acidity are a characteristic of many Sauvignon Blancs and Rieslings, and the buttery aromas of MLF can interfere with the fruity character of these wines as well.
What two techniques - that do not rely on concentrating grape sugars - can be used for sweet winemaking?
Stopping the fermentation with alcohol, SO2 or by cooling the wine (and filtering out the yeasts after). Think of Kabinett, Spätläse, sparkling Asti.
Add a sweetening component (RCGM or unfermented grape juice = Süssreserve)
Which techniques for sweet winemaking rely on concentrating grape sugars?
- Noble rot (Tokaij, Sauternes, Beerenauslese, Trockenbeerenauslese)
- Drying grapes on the vine (Passerilage, the grapes dehydrate).
- Drying grapes after picking (Passito, such as Recioto, again the grapes dehydrate)
- Freezing grapes on the vine (Eiswein, Icewine; there is ice in the grapes)
In all these, the sugars get so concentrated that the fermentation stops, resulting in low-alcohol (sometimes 7% for Trockenbeerenauslese) wines.
Name two advantages and one disadvantage of using stainless steel tanks instead of concrete vessels for maturation of the new wine.
Advantages:
- Easier to clean
- Detailed temperature control mechanisms can be used
Disadvantage:
- More expensive temperature control
Sometimes the winemaker chooses for controlled exposure of the must to oxygen before fermentation. Why would he do this, and what can be a reason not to do this?
For non-aromatic grape varieties, this is thought to improve the wine’s ability to age. For more aromatic grape varieties, however, one can lose some of the more delicate aromas.
Describe 3 fermentation styles of premium Pinot Gris and Chardonnay wines.
Fermentation in stainless steel or concrete: retain fresh fruit flavors (Chablis, Pinot Grigio from north-east Italy, Pinot Gris New Zealand)
Fermentation in large oak vessels: Pinot Gris in Alsace
Small, new oak vessels: Chardonnay from Cote d’Or
