What color grapes can be used to make white wine?
Predominantly white grapes, but many red/black grapes may also be used.
What are some important considerations winemakers have to weigh before processing and fermenting white grapes?
- Length of skin contact, if any
- Fermentation temperature
- Fermentation vessel
- Use of lees
- Malolactic fermentation - whether or not they’ll allow it and to what degree later on
What chemical can be used at multiple points during the winemaking process to prevent oxidation and inhibit the growth of microorganisms?
Sulfur dioxide (SO2)
What are some of the effects Sulfur dioxide (SO2) has on wine?
SO2 acts as an:
- Antiseptic (kills microorganisms)
- Antioxidant (binds with oxygen)
What are four commonly practiced must adjustment techniques?
- Adding RCGM (Rectified Concentrated Grape Must - raises alcohol in final wine because more sugar is made available for yeasts to turn into alcohol)
- Removing water (concentrates sugars - which can lead to higher alcohol in final wine - and concentrates tannins, acids, flavor compounds, and any faults, too)
Which acid is typically used to acidify a wine?
How is a wine deacidified?
By adding an alkali (an acid neutralizer).
What is the most common must adjustment made to white grapes from warm/hot climates?
What is the difference between enrichment and chaptalisation?
Both are adding sugar before or during fermentation in order to increase the alcohol level in a wine, but which term used depends on the TYPE of sugar used.
Enrichment uses RCGM;
Chaptalisation uses dry, non-grape sugar, e.g. sugar beet.
see p.47 in the textbook
Why do most winemakers avoid skin contact on their white wines
To reduce the risk of oxidation and the extraction of unwanted flavors.
Why would some winemakers keep white wine juice in contact with the grape skins?
Because skin contact increases flavor intensity and texture.
If a winemaker is doing skin contact for a white wine, how long will the juice stay in contact with the skins?
Usually only for a few hours.
When are grapes for white wines pressed?
Before fermentation (ideally, shortly after they’re harvested and brought to the winery).
What three techniques can a winemaker use to clarify the must of a white wine?
What are the two methods of filtration?
- Depth filtration
- Surface filtration
What is sterile filtration?
When a wine has gone through surface filtration with a filter with pores so small that the filters remove yeast and bacteria.
Describe what happens during surface filtration.
Surface filters look like very fine sieves, so as wine flows through this filter solid particles are captured on the surface. They can clog easily so generally they’re used AFTER depth filtration.
Describe what happens during depth filtration.
Thick filters have wine passed through them to trap solids, such as gross lees
This type of filtration can handle very cloudy wines
What can happen to a white wine if the winemaker does not clarify the must adequately?
Unpleasant aromas can form from microbiological issues and fermentation may stop.
Why do some winemakers choose not to over-clarify their white wine musts?
Some winemakers believe that having a small amount of grape solids in a fermenting must will make the resulting wine less prone to oxidation; additionally, they feel these solids will contribute complex flavors and a more pleasing texture to the final wine.
What is the most commonly used yeast strain in winemaking?
Why is it preferred?
This yeast strain is preferred because of its hardiness against SO2 and elevated levels of alcohol.
What are the two sugars found in grapes which are easily converted into alcohol?
What aspects of winemaking will determine the speed of fermentation?
- Type and quantity of yeasts;
- Nutrient content in the must;
- Concentration of sugars in the must;
- Temperature (warmer temperatures mean faster fermentations);
- How much SO2 is used (too much slows fermentation).
What is the optimum fermentation temperature for white wine?
Between 12°C - 22°C (54°F - 72°F)
What may happen if white wines are fermented at too low a temperature?
- Yeasts may go dormant, but they can be woken up with an increase of heat;
- Low fermentation temperatures may result in “pear drop” or pear candy aromas and may prevent a grape’s true varietal aromas from developing.
What may happen if white wines are fermented at too warm a fermentation temperature?
- Yeasts may die;
- Hot fermentation temperatures will sometimes create unappealing aromas, and there is a risk that the classic varietal character will be lost in the process.
What kinds of vessels are commonly used to ferment white wines?
- Steel tanks
- Oak barrels
What are the advantages of fermenting white wines in stainless steel?
- Stainless steel is inert (non-reactive), which helps maintain varietal character;
- Temperature control systems are easier to build into stainless steel fermenters than oak or cement.
What are the advantages of fermenting in oak barrels?
- Oak barrels are known to transfer heat effectively;
- Oak barrels will add richer flavors and rounder textures.
What will cause a fermentation to cease (aka a stuck fermentation)?
- All available sugar in a must is consumed;
- Yeasts run out of nutrients to metabolize;
- Temperatures exceed 35ºC (95ºF)
What are some potential complications a winemaker can run into during fermentation?
- Yeast nutrient deficiencies in the must, which can lead to stuck fermentations or off-odors;
- Carbon dioxide poisoning.
What are some important considerations winemakers must take into account post-fermentation in re: white wines?
- What vessel to use (oak, stainless steel, etc.)
- Whether to blend or not;
- Whether to lees age or not;
- Whether to allow, actively encourage, or completely block MLF;
- Whether to fine or filter the wine, and how much.
What are some of the benefits of blending white wines post-fermentation?
Blending helps the winemaker:
- improve consistency, texture, or flavor;
- enhance balance;
- create wines of a particular or desired style.
What flavors will aging in new oak add to white wines?
Oak aging is known to add flavors of vanilla, toast, clove, dill, nutmeg, coconut, butterscotch, anise, and smoke.
What less-costly methods may be substituted for oak barrels but still add desirable oak flavors to value-priced white wines?
The use of oak staves or oak chips.
The oak flavors will be less well integrated into the final wine as oak barrels do more than just add oak flavors, which is why this cheaper method is never used for premium white wines.
What is RCGM?
Rectified Concentrated Grape Must
This important component is used to adjust the sweetness level of a wine without impacting other elements (e.g. acidity or color).
What is bâtonnage and what are its benefits?
Bâtonnage is when a winemaker stirs the lees (dead yeast cells) that fell to the bottom of a fermentation vessel, breaking them open so they release amino acids.
The amino acids add more creamy, round, and mouth-filling elements resulting in a wine with greater complexity and mouthfeel.
What is malolactic fermentation?
Malolactic fermentation is a conversion of tarter, less chemically stable malic acid (the same acid in an under-ripe apple) into softer, creamier, and more stable lactic acid (the same acid in milk or yogurt).
What are some notable effects of malolactic fermentation?
- Lowers overall acidity;
- Creates the aroma of movie theater popcorn butter or melted butter (a compound called diacetyl)
- Creates a little CO2
What are some ways to prevent malolactic fermentation?
- Adding SO2 after primary fermentation completes;
- Storing the wine at cool temperatures;
- Sterile filtration.
What are some ways to encourage malolactic fermentation?
- Not adding SO2 or keeping levels very low;
- Warm storage temperatures.
What white grape varieties are most likely to undergo malolactic fermentation?
Chardonnay and Viognier
What’s the difference between fining and filtering?
Fining removes the small stuff you can’t see - all the unstable, microscopic things in a wine (proteins, phenolic substances, etc.). If these things aren’t removed prior to bottling they can clump together later and make the wine appear hazy. To remove these microscopic things, a fining agent is added that bonds with these constituents causing visible clumps to form (which can then be removed by filtering).
Filtering removes the big stuff you can see - all the large clumps (e.g. seeds, grape skins, pebbles, spiders) and smaller things like gross and fine lees.
Winemakers should ensure their wines are stable in what three areas?
How does a winemaker remove tartrate crystals?
By bringing down the wine’s temperature to 0ºC (32ºF) or colder for 1-2 weeks.
The crystals will precipitate out of the wine (they’re about the size of raw sugar crystals) and the winemaker filters them out.
What kinds of wine are susceptible to microbiological instability?
What kinds of wine are not easily susceptible to microbes?
- wines that haven’t gone through MLF
- wines with low or moderate alcohol
- wines low in acid
- wines with some residual sugar
- wines high in alcohol
- wines high in acid
- wines that have gone through MLF
What color will a white wine turn if it’s exposed to too much oxygen?
Wine is made out of grapes, which are a fruit - and most fruits will turn brown if you leave them exposed to oxygen too long (e.g. leaving an apple or avocado uncovered on your kitchen counter).