• Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

Card Range To Study

through

image

Play button

image

Play button

image

Progress

1/36

Click to flip

Use LEFT and RIGHT arrow keys to navigate between flashcards;

Use UP and DOWN arrow keys to flip the card;

H to show hint;

A reads text to speech;

36 Cards in this Set

  • Front
  • Back
The major advantages of S. cerevisiae over wild yeast are its
alcohol tolerance and its SO2 insensitivity
4 DISADVANTAGES OF WILD YEASTS are
1. They produce compounds that result in off flavors.
2. They are alcohol intolerant. Most wild yeast tolerate only 4 to 6% ethanol (some will tolerate 10%), and thus cannot convert all the sugar in grape juice to ethanol. Not only will the alcohol content of the wine be too low, but the residual (unfermented) sugar can contribute to subsequent instability in the wine.
3. They are unpredictable. The winemaker cannot anticipate the progress of the fermentation.
4. They are SO2 sensitive and will thus be inhibited by the SO2 (sulfur dioxide) that is normally used in winemaking. The winemaker is able to exploit this sensitivity by using SO2 to eliminate these organisms in favor of wine yeast
7 CHARACTERISTICS OF A GOOD WINE YEAST STRAIN are
1. Reproducible and predictable fermentation characteristics
2. Vigorous fermentation (in order to outcompete spoilage organisms)
3. Complete fermentation (to dryness, so that no sugar is left for spoilage organisms)
4. Good alcohol tolerance (most commercial strains will tolerate up to 17 to 18% ethanol)
5. High temperature tolerance (especially important at high ethanol concentrations)
6. Minimal off flavors, e.g. H2S
7. SO2 tolerance (so that unwanted microorganisms can be preferentially inhibited)
6 REQUIREMENTS FOR GOOD FERMENTATION are
REQUIREMENTS FOR GOOD FERMENTATION
1. SUGAR. Wine yeast can use glucose and fructose (the monosaccharide sugars found in grape juice) and sucrose (table sugar), a disaccharide that it must separate into its two monosaccharide components (glucose and fructose). It can also use some other sugars, but it cannot use starch.
2. NITROGEN. Ample nitrogen is usually contained in the various nitrogenous compounds in the grape juice. If necessary, diammonium phosphate (DAP) may be added as a nitrogen (and phosphorus) supplement.
3. VITAMINS. Yeast can make all the vitamins it needs except biotin, which it must obtain from the grape.
4. MINERALS. Especially phosphorus
5. LOW pH. The relatively acid environment of grape juice (pH between 3 and 4) is just right. This is too acidic for many food spoilage organisms.
6. TEMPERATURE BETWEEN 50° AND 100°F (20° to 40°C). Fermentation is very slow below 50° and is fastest at 80 to 85°F. Yeast can survive to about 110°F (45°C), but as the ethanol concentration incr
what temperature change can occur with each degree drop in brix?
A reduction in sugar of 1°Brix (about 1% sugar) results in a temperature rise of 2.3°F (1.3°C). This heat generation is extremely important because it can result in a fermenting must that reaches a temperature high enough to kill the yeast.
approximately what % alcohol is produced with an initial brix of 20?
The approximate ethanol yield by volume is 55%. Thus, a juice that is 20% sugar (20° Brix) will produce a wine that is about 11% ethanol by volume.
What is the most important determinant in fermentation time. Does white or red wine take longer to ferment?
Temperature is the most important determinant of fermentation time. Fermentation proceeds faster at higher temperatures. Since white wines are typically fermented at a lower temperature (55 to 70°F or approximately 12 to 15°C) than are red wines (70 to 90°F or 20 to 30°C), white fermentations typically require a longer time to be completed. Fermentation time can also differ significantly for different grape varieties.
what is the most common cause for stuck fermentation? Is white or red must more likely to get stuck? what are some remidies for stuck fermentation
If some nutrient becomes limiting or the environment becomes inhospitable before all the sugar is fermented, fermentation will stop, leaving unfermented residual sugar. Stuck fermentations are usually due to nitrogen or phosphorus deficiency in the grape juice, both of which can be treated by the addition of DAP. White fermentations are more likely to stick than reds because white must lacks the nutrients that are provided by the skins and seeds that are present in red fermentations. Excessively low or high temperatures can also cause a fermentation to stick. Heating a too-cold fermentation may re-start fermentation, but cooling a too-hot fermentation will not help if the high temperature has already killed the yeast. More yeast must be added
What is Malo-lactic fermentation. What bacteria is used to produce this fermentation process?
Lactic acid bacteria (the most important of which is Leuconostoc oenos) are responsible for malolactic fermentation, the conversion of malic acid to lactic acid. One of the 2 acid groups of malic acid is removed and converted to carbon dioxide, leaving lactic acid, which has only 1 acid group.
What affect does MLF have on wine? What can prevent MLF from occuring?
Malolactic (ML) fermentation reduces the acidity of the wine, generates CO2, and contributes a buttery flavor (imparted by a chemical compound called diacetyl). It occurs naturally in some wines, and almost always in wood tanks or barrels, but it can be prevented by SO2 or sterile filtration. It can be induced by inoculation with ML bacteria. It occurs in most red wines and about 20% of white wines, particularly barrel fermented Chardonnay. Malolactic fermentation increases the stability of the wine because once it has been completed it cannot occur again after bottling
What happens if MLF occurs in the bottle?
Malolactic fermentation in the bottle is undesirable because it will produce CO2 that cannot escape, so the wine will be fizzy, and the growth of the ML bacteria will cause the wine to be cloudy.
What is responsible for converting wine to vinegar?
Acetobacter is the bacterium responsible for the production of vinegar. It is usually present in all wineries.
What can be done to prevent the production of acetic acid?
In the presence of oxygen, acetobacter converts ethanol to acetic acid and ethyl acetate. The reaction can be prevented by excluding air. Acetobacter is also inhibited by alcohol concentrations above 14% and by SO2
What is Brettanomyces?
How does it affect wine?
Brettanomyces is a wild yeast that contributes a sweaty, leathery smell to wine. It is hard to control because it is ethanol tolerant and grows under much the same conditions as wine yeast. It can, however, be controlled by SO2. Some people like the “brett” character and it is a normal part of some traditional wines. It is especially prevalent in organic wines in which both SO2 use and filtration are minimized, either of which would control it.
The final alcohol concentration (expressed as percent alcohol by volume) can be roughly estimated by
multiplying the sugar concentration in the fruit (expressed as degrees Brix, roughly equivalent to percent sugar) by 0.55.
What is the U.S. upper limit for % ETOH by volume for table wine?
What brix does this correspond to?
(the U.S. lower limit for wine is
14%.
25.5
7%
Titratable acidity, is expressed as?
the typical range of TA is?
gm/100ml tartaric acid
0.6-0.8 gm/dl
The product of crushing, called the must, consists of approximately
80% juice, 16% skins and 4% seeds.
Most of the tannins, which are important for flavor and aging, are found in the
seeds (70%). The rest of the tannins are in the skins and a little is in the juice
Wine sold in the U.S. must carry the phrase "contains sulfites" on the label if the concentration is above
10 parts per million, whether or not SO2 was actually added.
Acidity may also be adjusted. In California, acidity is more often
too low than too high and is adjusted by the addition of tartaric acid to the juice
One ton of grapes typically yields
140 to 190 gallons of juice or wine
Red grapes yield more than white grapes (red grapes average?
175 gallons per ton vs. 150 gallons per ton for white grapes)
because red grapes are pressed after fermentation, when liquid can be more fully extracted. Also, red wine can be pressed harder than white wines because the tannin concentration that increases as more pressure is applied to the seeds and skins is not undesirable in red wines.
White wines are typically fermented at what temperatures?
(55 to 70°F)
Red wines are typically fermented at what temperatures?
(70 to 90°F)
What takes longer to ferment red or white wine? Why
White fermentations take much longer (10 to 30 days) than red fermentations (4 to 12 days) partly because they are conducted at a lower temperature and also because they do not contain the skins and seeds and other solid material that can provide nutrients and attachment surfaces for yeast. Some varieties ferment faster than others, presumably because they are a better source of certain yeast nutrients.
What is fining? what can be used to improve the clarity of wine? what products in wine cause cloudy or hazy changes?
FINING: Despite several rackings, wine may still be hazy because of protein, polysaccharide, or microbial residues. These, as well as excessive tannin, can be removed by treating the wine with a fining agent that when mixed with the wine reacts with or adsorbs the substance, precipitates out and falls to the bottom. The wine can then be racked or filtered to remove the substance. Egg white, gelatin and casein (milk protein) all remove tannins and other phenolic substances. Bentonite (a clay) removes protein hazes. Certain enzymes will break down and remove polysaccharides. Fining improves the clarity of wine but excessive fining may also eliminate flavor components that contribute to the complexity of wine flavor.
What can cause a wine to develop crystals? What can be done to prevent this phenomenon?
TARTRATE STABILIZATION: Over time, and especially when wine is refrigerated, the potassium and tartaric acid in wine can form a crystalline precipitate, potassium acid tartrate (KHT). This can alarm consumers because they may think it is an impurity or they may even mistake the crystals for broken glass. This problem can be prevented by cold stabilization—chilling the wine below 32°F for several weeks to cause the KHT to precipitate in the winery, where it can then be removed by racking or filtration before the wine is bottled. Alternatively, ion exchange can be used to replace the potassium ions with sodium ions or hydrogen ions, resulting in a more soluble form of tartrate that will not precipitate out.
What are some reasons to sterile filter a wine?
FILTRATION: The wine may be further clarified and stabilized by passing it through various filters. Diatomaceous earth (DE) (as is used in swimming pool filters) is a common filtration agent used to remove particulate matter. Any microbes that may lead to microbial instability problems in the bottle can be removed by sterile filtration. Sterile filtration is especially important in wine containing residual sugar that could serve as a substrate for remaining yeast cells. It is also important in wine that has not undergone malolactic fermentation, since the wine could later undergo malolactic fermentation in the bottle if malolactic bacteria are present. As with excessive fining, excessive filtration can reduce the flavor complexity of a fine wine. Many small premium winemakers minimize filtration, or even avoid it altogether, if their wine is completely dry, has completed malolactic fermentation and has been racked to the point of satisfactory clarity.
What should be done at bottleing time?
BOTTLING: Wine to be bottled is usually transferred to a holding tank near the bottling area. It is usually treated with SO2 at this time. The bottling line may be located within an enclosed clean space. Bottles are usually turned upside down and rinsed with hot water just before they are filled. They may also be sparged with nitrogen. A cork is inserted into the bottle immediately after it is filled. If the fill volume has been correctly adjusted, there will be minimal head space (the air space between the top of the wine and the bottom of the cork). The label is then applied to the bottle and the bottles are placed into case boxes. These are then stacked and stored to allow bottle aging, from a few months for white wines up to two years for some red wines. Alternatively, the labels may be applied after bottle aging if the bottles are to be stored in a humid cellar that might damage the labels. During bottle aging, the wine can be further monitored to detect any instability problems.
what afeects colror and tannin levels in red wines?
Color and tannin extraction are carefully managed in red wine fermentations by controlling the amount of skin contact. Both are increased by higher temperature, by alcohol concentration and by the amount of time before pressing.
when is color extraction in red wine complete? How can more tannins be extracted ?
High-priced red wines usually have longer skin contact, but the time can vary from 10 to 30 days (long after fermentation has finished). Such extended maceration does not increase the color of the wine (which peaks after only 3 to 5 days of skin contact) but does increase the tannin concentration of the wine, making a wine that is more bitter and astringent.
Thus the degree of extraction of the phenolic color and astringent components is a key factor in red wine style. High tannin levels are associated with long aging, but make a young wine less pleasant to drink. So in order to make a wine that is ready to drink upon release, the tannin levels must be moderate, while an expensive wine destined for long cellaring must have higher levels. Other factors, such as the fruitiness in the wine must be in balance with the level of tannin or else the wine will be considered defective.
What is carbonic maceration?
CARBONIC MACERATION: This is a red wine variation in which whole berries are blanketed with CO2 and left for 8 to 10 days, during which chemical changes take place inside the berries, including the conversion of some sugar into alcohol. Eventually the skins break open and the must is pressed, inoculated and allowed to ferment normally. This process produces a very fruity, low tannin, light red wine. It is used to produce nouveau (“new”) wines that are released only a few weeks after harvest. The most famous of these is Beaujolais Nouveau, from the Beaujolais region of France, which receives tremendous publicity each year when it is released simultaneously all over the world on the third Thursday in November
Name the wine regions of france
wine map of france
wine map of france 2