Vinification Flashcards
1
Q
How oxidation can be reduced when harvesting
A
- Limit air contact; some harvest trailers will immediately blanket grapes with carbon dioxide or nitrogen
- Add small amounts of SO2
- 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
2
Q
Decisions winemakers have to make after harvesting the grapes
A
- De-stem or not
- Crush or not
- Type of press to use
- Amount of SO2 to use
- Must treatments to use
3
Q
Effects of destemming
A
- Most white grapes and majority of red grapes are destemmed
- Destemming isn’t appropriate for sparkling wine production or for wines undergoing carbonic maceration
4
Q
Advantages of destemming
A
- 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
- In red winemaking stems have been found to release water and potassium, which is undesirable; they also absorb color and alcohol, also considered undesirable
5
Q
Disadvantages to destemming
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
- Pressing without the stems is slower as the stems provide drainage channels
6
Q
Advantages of whole cluster pressing
A
- Releases very fine juice with low phenolics and low solids, due to the rapid drainage
- Reduces compaction of the pomace cap in the fermentation tank
- Makes 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, stems can release good quality tannins which reduce the damage done by oxidation and can help to fix color in the wine
7
Q
vertical screw press
A
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
Advantages:
- simple and easy to use
- juice is filtered through the grape stalks/pomace as it is extracted, giving a reasonably clear must or wine
Disadvantages:
- 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
8
Q
horizontal screw press (vaslin press)
A
- Basically a basket press turned on its side, with pistons at either end
- Fuit is loaded through an opening on the top
Advantages:
- 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
Disadvantages:
- 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
9
Q
pneumatic press
A
- Basket press again turned on its side, but inside is a cylindrical pneumatic bag or membrane which is inflated by compressed air or even water
- The bag squeezes the grapes gently against the perforated drum in the middle, the juice goes through these holes and is collected beneath the press
Advantages:
- 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
Disadvantages:
- the press cycle is slightly longer than with the horizontal screw press
10
Q
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
- Grapes or pomace are placed into a non perforated cylindrical tank and then pressed against internal drains by an inflatable membrane
Advantages:
- 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
Disadvantages:
- 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
11
Q
Continuous Screw Press
A
- 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
Advantages:
- as the press can be continually loaded with grapes, a very high throughput can be achieved
Disadvantages:
- 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
12
Q
SO2 in must treatments
A
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.
13
Q
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
- Clear must is then racked off
- Pectolytic enzymes may be added, which aid the settling process and increases the proportion of clean juice that can be extracted
- Other juice clarification methods exist, but may not produce as high quality grape musts as natural settling
14
Q
Amount of sugar required to raise alcohol by 1% abv in wine
A
whites:
- 17g/l of sugar raises the abv 1%
reds:
- 19 g/l of sugare, due mostly to a higher level of evaporation at higher fermentation temperatures and in pumping over
15
Q
Optimum temperature range for fermenting both red an white wines
Effects of excessively high or low temperatures
A
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
20
Q
puncheon
A
500 liter barrel
24
Q
2 major categories of all species of oak
- Species important to wine production
- 3 species that fall under that category
A
- Red and White oak
- White oak is important; Red oak is porous and thus not suitable for cooperages
-
Quercus alba
- American White Oak
- Low phenols but high aromatics, particularly methyloctalactones (coconut aroma)
-
Quercus petraea
- Tighter grained, fewer extractable tannins, high aromatic potential (e.g. lactones, volatile phenols such as eugenol {Clove aroma}, and phenol aldehydes such as vanillin)
-
Quercus robur
- Pedunculate oak; low odoriferous compounds but high extractable polyphenol content
25
Q
Two types of European Oak
A
- French Oak (Quercus robur) - common throughout Europe
- Sessile Oak (Quercus petraea) - finer grain species, more sparse
26
Q
3 main forests for French oak
A
- Alliers
- Vosges
-
Tronçais (sub-section of Allier)
- Top 3 command the highest prices (upwards of $4,000 per barrel)
- Limousin oak - more loose-grained, better suited for Cognac, Armagnac, Sherry, and whiskey aging
27
Q
6 main French forests known for oak
A
- Limousin
- Vosges
- Nevers
- Bertranges
- Allier
- Tronçais (sub-section of Allier)
