Vinification Flashcards Preview

Viticulture / Vinification > Vinification > Flashcards

Flashcards in Vinification Deck (21):

What are some ways that oxidation can be reduced when harvesting?

  • limit air contact; some harvest trailers will immediately blanket grapes with carbon dioxide or nitrogen
  • add small amounts of SO2
  • the rate of oxidation increases as temperature rises; harvesting early in the morning or at night is best when the ambient temperature is coolest
  • delays provide more opportunity for all threats; grapes should be processed as quickly as possible after the harvest


What are some decisions winemakers have to make after harvesting the grapes?

  • to de-stem or not
  • to crush or not 
  • type of press to use
  • amount of SO2 to use 
  • must treatments to use


What are the effects of destemming?

Most white grapes and majority of red grapes are destemmed. Destemming isn't appropriate for sparkling wine production or for wines undergoing carbonic maceration.


  • if unripe, removes bitter and herbaceous aromas from entering the wine 
  • removal of material other than grapes
  • in white winemaking, allows more fruit to fit into press, making grape processing more efficient overall
  • pressing whole bunches helps release very fine juice with low phenolics and low solids, due to the rapid drainage 
  • the presence of stems will reduce compaction of the pomace cap in the fermentation tank and make temperature control and phenolic extraction easier, therefore some winemakers choose to add a small percentage of stalks to the fermentation vessel 
  • in some black grape varieties, the stems can release good quality tannins which reduce the damage done by oxidation and can help to fix color in the wine


  • a poor quality destemming machine will damage the stems so badly that more bitter and herbaceous flavors will be released than if no distemmer was used to begin with 
  • pressing without the stems is slower as the stems provide drainage channels 
  • in red winemaking stems have been found to release water and potassium, which is undesirable; they also absorb color and alcohol, also considered undesirable


What is a vertical screw press?

Grapes are placed in a cylindrical basket, a removable lid is then placed on top. Pressure is then manually applied and liquid is collected at the bottom of basket and drains away to the vat.


  • simple and easy to use 
  • juice is filtered through the grape stalks/pomace as it is extracted, giving a reasonably clear must or wine


  • filling and reloading press is slow and labour intensive
  • the pressing process itself requires time and shouldn't be rushed, which risks extracting bitter phenols as well as juice/wine
  • the extracted liquid is exposed to oxygen which risks oxidation

A image thumb

What is a horizontal screw press (vaslin press)?

Basically a basket press turned on its side, with pistons at either end. The fruit is loaded through an opening on the top.


  • filling and emptying is simple
  • operation can be completely automated
  • extracting liquid can be partially protected from oxidation by blanketing the receival tray with inert gas


  • breaking up the marc between press cycles is quite violent, resulting in an extraction of phenolic and astringent matter from the skins seeds and stems 
  • high pressures can be used, reducing potential quality

A image thumb

What is a pneumatic press?

A basket press again turned on its side, but this time inside is a cylindrical pneumatic bag or membrane which is inflated by compressed air or even water. This bag squeezes the grapes gently against the perforated drum in the middle, the juice goes through these holes and is collected beneath the press.


  • even at low temperatures there is good extraction, this higher quality is achieved 
  • the breaking of the pomace between press cycles can be gentle, reducing the extraction of bitter phenolics 


  • the press cycle is slightly longer than with the horizontal screw press

A image thumb

What is a tank press?

A variant of the pneumatic press. Pressing occurs inside a closed tank, which can be pre flushed with inert gas, thus preventing oxygen exposure. Here the grapes or pomace are placed into a non perforated cylindrical tank and then pressed against internal drains by an inflatable membrane. 


  • oxygen contact with the extracted liquid can be limited 
  • the breaking of the pomace between press cycles can be gentle, reducing the extraction of bitter phenolics 


  • due to the pressing surface being smaller than a similarly-sized pneumatic press, the press cycles are usually longer
  • tank press is the most expensive type of press 


What is a Continuous Screw Press?

Consists of a perforated drum with an Archimedes screw inside. Grapes or pomace are loaded into one end of the press, the screw then pushes the grapes towards a resistance at the far end so that the liquid is expelled out of the drums perforations.


  • as the press can be continually loaded with grapes, a very high throughput can be achieved


  • quality of juice extracted is not as god as in the batch process, due to higher pressures being applied and the rough action of the screw


What is the role of SO2 in regard to must treatments in winemaking?

Has been used at least since the 17th century. It is produced in small quantities (10mg/L) by yeast during fermentation so a total absence is very rare.

It has four main properties:

  • Antiseptic: Inhibits development of microorganisms (e.g. Acetobacter and wild yeasts -- selected yeasts are usually more tolerant 
  • Antioxidant: Combines with oxygen, removing it before harm can be done
  • Antioxidasic: Denatures oxidasic enzymes (i.e. Laccase)
  • combines with Acetaldehyde, a byproduct of oxidation 

Preparations and usage -- it is added in one of these four forms:

  • potassium metabisulfate powder that, when dissolved in an acid solution, releases sulfur dioxide
  • pure SO2 gas compressed into liquid form
  • dissolved in solution (normally 5%)
  • Generated from burning sulfur tablets or candles, SO2 is often added before fermentation in order to control microbial activity and oxidation. It may also be added to the harvested grapes on the way to the winery. Here the powdered form is used.

General recommendations are as follows:

  • For white musts 60-100 mg/l
  • For red musts 10-60 mg/l

Levels are increased according to

  • style of wine (e.g. more sulfur is needed if it is a priority to retain primary aromas)
  • health of grapes at harvest; if some rot is present, amounts are increased
  • pH. Wines with higher pH levels need more SO2 because less is in the active form. Amounts of SO2 in wine are usually referred to as "Free and Total" by winemakers. Every time SO2 is added to a grape must or wine a percentage becomes "bound" and a percentage remains "free." What percentage goes to what form depends on many factors such as the prior level of SO2, the level of sugars, aldehydes, ketones, and the pH.

The Free SO2:

  • the portion that is active and has protective properties
  • A portion of this dissolves in the water present in the wine to form sulfurous acid, the other remains as "Molecular SO2," which strictly speaking, is the only one with any protective properties. The amount of free SO2 that forms sulfurous acid is pH dependent. The higher the pH the higher proportion remains as molecular SO2, German Riesling for instance!

The Bound SO2:

  • The portion os SO2 that has bound to sugars, aldehydes, and ketones. Once it has combined, it is rendered inactive.

The Total SO2:

  • The sum of free and bound SO2 in wine. Sweet wines are generally allowed higher levels of SO2 due to the binding power of sugars. Organic wines are required to have less.


What is cold settling?

A simple and effective juice clarification method where natural settling occurs by gravity. Freshly pressed grape must is settled for a period of time , usually overnight and during this time the sediment settles to the bottom of the vat. The clear must is then racked off. Pectolytic enzymes may be added, which aid the settling process. They increase the proportion of clean juice that can be extracted. Other juice clarification methods exist but they are arguers not to produce as high quality grape musts as natural settling.


How much sugar does it require to raise the alcohol by 1% abv in wine?

Each kg of sugar increases the volume of the wine by .63 litres 

For whites:

  • raising the abv by 1% requires 17g/l of sugar

For reds:

  • 19 g/l are required; due mostly to a higher level of evaporation at higher fermentation temperatures and in pumping over


What is the optimum temperature range for fermenting both red an white wines?; what are the effects of excessively high or low temperatures?

Whites - generally fermented at 10-18˚C

Reds - generally fermented at 20-32˚C

Excessively High Temperatures:

  • encourage oxidation
  • lead to the loss of aroma and flavor compounds, and sometimes even alcohol due to volatilization
  • may result in the yeast becoming sluggish, and if the temperature goes above 35-38˚C the fermentation may even stop

Excessively Low Temperatures:

  • white wines: may lead to the retention of isoamyl acetate (banana/pear drop aromas) which is usually not desirable 
  • red wines: will lead to a poor extraction of color and tannin
  • can cause sluggish fermentations 
  • may lead to the production of high levels of ethel acetate, giving the fermenting must and resulting wine a volatile aroma


What is a stuck fermentation and why does it occur?

This is when a fermenting grape must stops fermenting. This can happen for a variety of reasons:

  • The fermentation may be too hot or too cold for good yeast activity
  • Nutrient levels may be depleted, preventing proper yeast activity
  • If the fermentation was uninoculated, the indigenous microflora may have died off prior to the conversion of all of the sugar due to the intolerances of alcohol.

There are several ways to restart it:

  • Adjust the temperature to a more suitable level
  • Increase nutrient levels by adding nitrogen rich products such as di-ammonium phosphate or thiamine
  • Re-innoculate, either by adding an active dry yeast culture or by cross-inoculating from a different active ferment. Problems with stuck fermentations include the generation of large amounts of hydrogen sulfide, increased VA, the risk of microbial spoilage, and lastly the possibility that the fermentation will never complete, resulting in a sweet-ish wine.


What is the difference between drawing-off and direct pressing in regards to rosé winemaking?

Direct pressing 

  • literally when you directly press fresh harvested grapes, without a lengthy maceration of crushed grapes
  • Caution is required not to extract too much tannin
  • Resulting wine will be pale pink and is treated as a white must
  • Examples are found in France's Cotes de Provence and Languedoc

Drawing-off (Saignée)

  • Most widely used rosé winemaking method
  • Crushed grapes are macerated for 6-48 hours -- the longer the maceration the darker the color
  • Examples include Anjou Rose, Bordeaux Clairet, and Cotes de Provence


What is cold soaking?

De-stemmed and crushed grape must is cooled below 15˚C and kept at this temperature for a period of time (3-7 days) in order to aid color extraction. Where this is done, higher amounts of SO2 are added (80-100mg/l) to prevent spontaneous fermentation from taking place.


What is the effect of temperature in fermentation of a red wine?

Moderate Temperatures (25˚C) favor good color extraction, preservation of primary fruit aromas, and middle to moderate tannin extraction. The higher the temperature, the more tannin will be extracted.


What is a puncheon?

 500 liter barrel

A image thumb

What is the difference between delestage, remontage and pigeage?

Both are Cap Management techniques.

Pigeage = Punching Down /  Remontage = Pumping Over / Delestage = Rack and Return

Pigeage: Punching Down

  • gentler than Remontage
  • pushes cap down by using a hydraulic piston
  • often chosen by Pinot Noir and Syrah producers; Cabernet and Merlot have shown to become more rustic when made this way
  • harsh/bitter compounds are less likely to be extracted from seeds or stalks
  • good dispersion of temperature
  • avoidance of bacterial spoilage on the submergence of the cap

 Remontage: Pumping Over

  • can be carried out with or without aeration
  • simple to perform, requires only a pump and a hose
  • excellent extraction achieved
  • enables aeration of the fermenting must, thus reducing reduction problems
  • exposure to oxygen aids yeast activity early on
  • widely used, especially for Cabernet and Merlot
  • usually results in rich, structured, full bodied wines with no trace of bitterness or vegetalness 

Delestage: Rack and Return

  • involves pumping the fermenting must from the bottom of the vat into a new vessel of comparable capacity, the remaining pomace falls to the bottom of the tank, then the must is pumped from the other tank back to the original one on top of the must
  • complete mixing and breaking up of the cap is achieved
  • allows for excellent aeration
  • good extraction of tannins, color pigments, and polysaccharides (pectins) from the fermenting grapes into wine
  • seeds can be removed from the bottom of the tank, which reduces the possibility of the extraction of bitter tannins
  • some winemakers argue that this method is too extractive


What are the environmental requirements for growth/control of MLF?

  • pH btwn 3.3-3.5
  • temp btwn 18-25˚C
  • less than 50 mg/l total SO2
  • a certain amount of nutrients (dead yeast cells, amino acids, vitamins)

MLF is inhibited by:

  • early clarification, usually by racking, which reduces nutrient and bacteria levels
  • SO2 addition after fermentation; free levels greater than 25 mg/l will inhibit bacterial growth, including lactic acid bacteria
  • storage temperatures below 12˚C
  • pH below 3.1
  • adequate cleaning and maintenance of containers
  • sterile filtration at bottling (to prevent MLF in a bottled wine)

MLF is encouraged by:

  • keeping wine on its yeast lees after fermentation
  • using low levels of SO2 before fermentation, and not adding it after fermentation until MLF has completed
  • maintaining wine at temperatures between 18-22˚C
  • increasing the pH to above 3.3
  • adding freeze dried MLF bacteria or adding lees from a tank already undergoing MLF


What is sparging?

Nitrogen is less soluble in wine than carbon dioxide, so it is used to 'sparge' a wine. 'Sparging' involves the passage of fine bubbles of nitrogen to a wine. This is done to remove dissolved oxygen from a wine or when additions are being made to a wine such as SO2. Nitrogen is more commonly used in red winemaking than with white wine, due to its low solubility.


What are the two major categories that all species of oak can be divided into?; which is important to wine production?; what are three species that fall under that category?

Red and White oak

White oak is important; Red oak is porous and thus not suitable for cooperages

Quercus alba - the American White Oak - low phenols but high aromatics, particularly methyloctalactones (coconut aroma) 

Quercus petraea - tighter grained oak, with fewer extractable tannins, and high aromatic potential (e.g. lactones, volatile phenols such as eugenol {Clove aroma}, and phenol aldehydes such as vanillin) 

Quercus robur - the pedunculate oak; this has low odoriferous compounds but high extractable polyphenol content