Vinification Flashcards
What is the process of alcoholic fermentation?
The metabolism of yeast cells converts sugar in grape must into ethyl alcohol (ethanol) and carbon dioxide (CO2).
List reasons a winemaker would add sulfur dioxide (SO2)? (4)
- Prevent oxidation
- Prevent Bacterial contamination
- Ensure rapid fermentation
- Eliminate any ambient yeast in favor of cultured yeasts.
What is volatile acidity?
VA is combination of 2 primary compounds, Acetic acid (essentially vinegar) and ethyl acetate (nailpolish remover aroma) . These compounds form when oxygen is exposed to acetic acid bacteria or when fermented sugars are exposed to a lactobacillus infection. The oxidative environment that the acetic acid bacteria is exposed to most of the time is generally large older casks ( think Nebbiolo from NW Italy.) The fermented sugars scenario I find happens in new world wines grown in warm climates (think Napa Cab, Zinfandel.)
In the case of blind tasting you would call VA, as “VA” you find these VA in wines such as Nebbiolo, high abv New World wines, Sangiovese that has been aged in large older bottle or casks.
When volatile acidity is encountered as a fault, excessive acetic acid has been produced by the activity of acetobacter, the group of bacteria responsible for turning wine to vinegar in the presence of oxygen. Acetobacter require oxygen for their growth and survival. The acetic acid (what acetaldehyde is converted into) reacts with alcohol to produce an ester known as ethyl acetate.
A few other acids such as formic, propionic, succinic, and lactic, normally present in trace amounts in wines, are also volatile.
Name two examples of sulfides found under reductive conditions?
Hydrogen sulfide (H2S) and mercaptans
What is the difference in fermentation between small vessels and large vessels in terms of temperature?
Without accounting for any temperature control, small vessels provoke slow, cool fermentations and large vessels lead to short, hot fermentations.
Between what temperatures will yeast act?
Between 50°F-113°F
Below 50°F, most yeasts will not act; above 113°F, yeasts will die
Red wine fermentations may reach into the 90s, although winemakers run the risk of volatized (lost) flavor compounds and stuck fermentations as the thermometer passes 95°F.
What is the benefit of hot fermentation for red wines?
Increased extraction of color
Tannin
Flavor compounds
What does bâtonnage do for a wine?
Adds further complexity and richness.
What are ambient yeast?
Yeast that are present in the vineyard and/or the winery and come to life in the presence of must, although they are by nature less predictable than cultured yeasts.
often inaccurately identified as native or wild yeast.
What is chaptalization?
The addition of sugar to the must to increase the final alcohol and glycerin content of the wine
Producers of Pinot Noir, most notably in Burgundy but also in Oregon and elsewhere, often add sugar during alcoholic fermentation, particularly towards the end, even if some might not readily confess to it. The aim is not primarily to increase the final alcohol level but to extend the fermentation and thereby improve the flavour and texture of the wine. It is said that earlier picking followed by this fractional chaptalization (which is less disruptive to yeast metabolism) often produces better results than fruit picked later with higher sugar levels.
Name three techniques used for alcohol adjustment
Chaptalization
Spinning cones
Reverse Osmosis
What is reverse osmosis?
List four reasons one may use reverse osmosis.
What is the permeate and retentate?
Legality?
Currently used chiefly for two distinct purposes: Alcohol reduction and must concentration. Also used to reduced excessive levels of VA and removal of negative flavor compounds that result from Brettanomyces spoilage.
-with adjusting alcohol, the process separates the wine into two constituent parts, permeate and retentate.
-permeate, which contains water and ethanol, is then distilled to a proper level before being recombined with the retentate—the wine’s aromatic compounds—at a lower percentage of alcohol.
-once banned in the EU, such processes of de-alcoholization by physical separation were legalized in 2009, provided the level of alcohol is not adjusted by more than 2%
-For must concentration, reverse osmosis is used to remove water from the unfermented grape must, achieving a similar result to vacuum evaporation. It has been widely adopted in Bordeaux, where many producers regard it as an insurance policy against the negative effects of a rainy harvest.
-Controversially, some have seen it as a way of producing more concentrated, denser wines of the sort that appeal to influential critics and the modern market place.
How is malolatic initiated?
What is the byproduct of malolactic fermentation responsible for buttery aromas?
-Malolactic fermentation may be initiated by inoculation, or it may occur naturally, as lactic acid bacteria are naturally found alongside yeasts on grape skins. It may also be prevented or shortened by removing the organisms responsible.
-Diacetyl
What is carbonic maceration?
an alcoholic fermentation used for some red wines, wherein whole, uncrushed grapes in an anaerobic environment (under a protective blanket of CO2) initiate an intracellular fermentation. Attempting to sustain itself, a berry will release enzymes to transform its own sugar into ethanol and carbon dioxide. This occurs without the action of yeasts. However, such fermentations cannot produce more than a couple of degrees of alcohol, as the berry ceases activity in the presence of enough ethanol. Carbonic maceration must therefore be combined with a standard fermentation in wine production.
The grape can develop an alcohol level of approximately 2% before it dies and the cellular activity ceases. The grapes may then rupture due to an internal build-up of carbon dioxide, or the winemaker may simply press the juice off the skins; either way, the wine ferments to dryness with the normal activity of yeast.
Semi-carbonic maceration is more common, and it is actually the more traditional technique in Beaujolais. Here, carbon dioxide is not added to the fermentation vat but produced naturally. Whole clusters at the bottom of the tank crush under the weight of those above and begin fermenting normally. As the carbon dioxide released by standard fermentation blankets the whole berries above, they begin to ferment internally. Typically, semi-carbonic maceration is conducted in an open vat.
What is the difference between whole cluster and whole berry fermentation?
whole clusters (retaining the stems), whole berries (discarding the stems)
Henri Jayer preached total de-stemming of Pinot Noir clusters prior to fermentation, but it is again fashionable to include some percentage of whole clusters in the vat. DRC and Dujac are high-profile practitioners of whole-cluster fermentation. Proponents believe when expertly handled one typically achieves more aeration and cooler temperatures during fermentation, lighter color, slight carbonic notes, and firmer tannins in the final wine. Advocates of whole-berry fermentation, in which the grapes are de-stemmed but not crushed prior to fermentation, can achieve some of the same high-toned, floral, carbonic aromatic complexity that results from whole cluster, without risking the green tannins that can prevail if stems are not properly lignified. Stems can also harbor potassium, raising pH in the final wine.
What are the pros and cons to whole cluster fermentation?
Pro: requires less handling while improving the movement of juice and air through the cap
Con: Damaged or unripe stems can cause undesirable green flavors in the wine
What is cold soak/pre-fermentation maceration?
What are the pros and cons?
Who used the technique? Who is against the technique?
-Wine making technique the maceration of grape skins with juice before the onset of alcoholic fermentation. The mass is held at a low temperature (39-50 degrees), for anything from 2-10 days, often along with sulfur dioxide additions, which may hold fermentation for the desired time.
Pros:
-theory that it adds more favorable combination of phenolics
-solution provides a good environment for extracting color, produces less astringent tannins, and enhances fruit aromatics in the wine
-mirrors the slow onset of fermentation that occurs naturally in Burgundy’s cool underground cellars, where yeasts take a few days to get moving.
-Cons:
-possibility of oxidation or spoilage from contamination yeasts
-possibility of unwanted fermentation kicking off
-seen as an intrusive technique and not adequately reflecting terroir
-Etienne Grivot (Domaine Jean Grivot) began using the technique in 1984 and accelerated its practice during the Guy Accad era of the late ’80s and early ’90s; believed 5-7 days improves a wine’s capacity to age and renders organic acids more stable.
-Jeremy Seysses of Fujac views cold soaking as “an element of convergence, when we are really trying to make wines that are different”
What is gained by the inclusion of grape skins to red wine fermentation?
Extract the phenolics contained within grape skins–tannin, color compounds (anthocyanins) and flavor compounds–with the help of heat and alcohol.
What could happen without cap management?
the cap will dry out, solidify and prevent extraction.
What are the three methods used for cap management?
Pigeage-“PEE-za-zhage” punching down
Remontage- “re-MOON-tage” pumping over
Délestage-“del-le-stage”; rack-and-return; Fully draining the fermentation vessel, racking the wine into a separate vessel, while the cap drains fully, and is then pumped back over the cap in the fermentation vessel
*all during fermentation, as opposed to soutirage which is post fermentation
What is the difference between a traditional basket press and a modern pneumatic bladder press?
Basket press relies on vertical pressure to press the pomace, whereas the modern pneumatic bladder press exerts gentle pressure on the grapes by means of its inflation with air.
What are the 5 most common methods of fining?
bentonite (type of clay)
casein (milk protein)
isinglass (material from sturgeon bladders)
gelatin
egg white
What do fining and filtration do to a wine?
Both processes ensure greater clarification in the finished wine, and filtration also promotes stability in the bottle
What is débourbage?
Settling
After pressing, allowing juice to settle so that the juice may be racked off suspended solids and clarified prior to fermentation
What is cold stabilization?
a process that causes tartrate crystals to precipitate out of the wine at a temperature of approximately 25°F. In white wines that are not cold-stabilized, crystals may later form in the bottle.
