Natural clarification takes place as wine ages in barrel, its suspended particles gradually falling to the bottom.
In
transparency. A wine with too much suspended matter will appear cloudy and dull, even if its aroma and flavor are unaffected; wines therefore generally undergo some kind of clarification.[1]
Before
colloids.[1] Pectins are structural molecules in the cell walls of fruits which have the important function of 'gumming' plant cells together. The pectin content of grapes increases steadily throughout ripening, reaching levels of about 1 g/L, although it varies by varietal and pre-fermentation handling processes. Large pectin molecules can affect the amount of juice yielded at pressing, ease of filtration and clarification, and extraction of tannins. Grapes contain natural pectolytic enzymes responsible for softening the grape berries during ripening, but these are not active under wine-making conditions (due to pH level, SO2, and alcohol.) Therefore, fungal pectolytic enzymes are often added to white must to break up pectins, decrease the viscosity of the juice, and speed up settling. In red musts, this increases color and tannin extraction.[2]
After fermentation, the force of
siphoned or "racked" off the compact solids into a new container.[3] But this process may take many months, or even years, as well as several rackings, in order to produce a perfectly clear wine. Producers can accelerate the process by using fining agents, filtration and/or flotation.[1]
University of California, Davis Department of Viticulture and Enology, however, found that no detectable amount of inorganic fining agents, and only trace quantities of proteinaceous agents, are left in the wine.[4]
There is the risk of valuable aromatic molecules being precipitated out along with the less desirable matter.
aroma from the phenols before they are removed.[citation needed
Diatomaceous earth, often used in depth filtration
While fining clarifies wine by
binding to suspended particles and precipitating out as larger particles, filtration works by passing the wine through a filter medium that captures particles larger than the medium's holes. Complete filtration may require a series of filtering through progressively finer filters. Many white wines require the removal of all potentially active yeast and/or lactic acid bacteria
if they are to remain reliably stable in bottle, and this is usually achieved by fine filtration.
Most filtration in a winery can be classified as either the coarser
μm is generally considered to result in a microbially stable wine and is accomplished by the use of membrane cartridges, most commonly polyvinylidene fluoride
(PVDF). Certain red wines may be filtered to 0.65 μm, to remove yeast, or to 1.0 μm to remove viable brettanomyces only.
Flotation
The winemaking technique of flotation was adapted from the
froth that can be removed from the wine. This must be done prior to fermentation, since yeast will inhibit the flocculation involved.[1]
Stabilization
Cold stabilization causes tartrates to crystallize and precipitate out of the wine.
As a complex chemical mixture dependent on the activity of microorganisms, wine can be
carbonic gas
.
Temperature instability
Tartaric acid
coagulate if exposed to excessively fluctuating heat; the use of fining agents such as bentonite can prevent the haze this causes.[1]
Microbiological instability
Dead yeast cells can leave wine cloudy, while active yeast may trigger further fermentation.
A wine that has not been sterilized by filtration might well still contain live yeast cells and bacteria. If both
alcoholic spirit to give a fortified wine of sufficient strength to kill all yeast and bacteria, or by pasteurization
.
Pasteurization gives a
kosher status.[citation needed] Typically, the wine is heated to 185 °F (85 °C) for a minute, then cooled to 122 °F (50 °C), at which temperature it remains for up to three days, killing all yeast and bacteria. It may then be allowed to cool, or be bottled "hot" and cooled by water sprays. Since pasteurization affects a wine's flavor and aging potential it is not used for premium wines. A gentler procedure known as flash pasteurization involves heating to 205 °F (96 °C) for a few seconds, followed by rapid cooling.[11]
Other methods of stabilization
Clarification tends to stabilize wine, since it removes some of the same particles that promote instability. The gradual
Some producers prefer not to thoroughly clarify and stabilize their wines, believing that the processes involved may diminish a wine's aroma, flavor, texture, color or aging potential. Wine experts such as
Port, may expect to see tartrates and sediment after aging in bottle.[1]
