Clarification and stabilization of wine

From Wikipedia, the free encyclopedia
  (Redirected from Clarification (wine))
Jump to: navigation, search
The winemaking process naturally produces sediments that can precipitate out of the wine.


Clarifying wine[edit]

Natural clarification takes place as wine ages in barrel, its suspended particles gradually falling to the bottom.


Before fermentation, pectin-splitting enzymes and, for white wine, fining agents such as bentonite may be added to the must in order to promote the agglomeration and settling of colloids later.[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 gravity may eventually cause the wine to "fall bright" or clarify naturally, as the larger suspended particles gradually settle to the bottom of the storage vessel. The wine can then be 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]


Main article: Finings

In winemaking, fining is the process where a substance (fining agent) is added to the wine to create an adsorbent, enzymatic or ionic bond with the suspended particles, producing larger molecules and larger particles that will precipitate out of the wine more readily and rapidly. Unlike filtration, which can only remove particulates (such as dead yeast cells and grape fragments), fining can remove soluble substances such as polymerized tannins, coloring phenols and proteins; some of these proteins can cause haziness in wines exposed to high temperatures after bottling. The reduction of tannin can reduce astringency in red wines intended for early drinking.[4] Many substances have historically been used as fining agents, including dried blood powder,[5] but today there are two general types of fining agents — organic compounds and solid/mineral materials.[4]

Organic compounds used as fining agents are generally animal based, a possible cause of concern to vegans.[6] The most common organic compounds used include egg whites, casein derived from milk, gelatin and isinglass obtained from the bladders of fish. Pulverized minerals and solid materials can also be used, with bentonite clay being one of the most common, thanks to its effectiveness in absorbing proteins and some bacteria. Activated carbon from charcoal is used to remove some phenols that contribute to browning as well as some particles that produce "off-odors" in the wine.[4] In a process known as blue fining, potassium ferrocyanide is sometimes used to remove any copper and iron particles that have entered the wine from bentonite, metal winery and vineyard equipment, or vineyard sprays such as Bordeaux mixture. Because potassium ferrocyanide may form hydrogen cyanide its use is highly regulated and, in many wine producing countries, illegal.[7] Silica and kaolin are also sometimes used.[4]

Some countries, such as Australia and New Zealand, have wine labeling laws that require the use of fining agents that may be an allergenic substance to appear on the wine label. A study conducted by the 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.[8] Some producers of premium wine avoid fining, or delay it in order to leach more flavor and aroma from the phenols before they are removed.


Main article: Filtration
Diatomaceous earth, often used in depth filtration


Most filtration in a winery can be classified as either the coarser depth filtration or the finer surface filtration.[4] In depth filtration, often done after fermentation, the wine is pushed through a thick layer of pads made from cellulose fibers, diatomaceous earth or perlite.[9] In surface filtration the wine passes through a thin membrane. Running the wine parallel to the filter surface, known as cross-flow filtration, will minimize the filter clogging. The finest surface filtration, microfiltration, can sterilize the wine by trapping all yeast and, optionally, bacteria, and so is often done immediately prior to bottling. An absolute rated filter of 0.45 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.

A lot of companies at the moment use the fine clay filter aid kieselguhr, which is carcinogen, to filter liquids destined for human consumption. The EU-Funded project Adfimax is studying a novel vegetable fibre-based alternative which performs better and is sustainable as well.[10]




Cold stabilization causes tartrates to crystallize and precipitate out of the wine.


Temperature instability[edit]


Microbiological instability[edit]

Dead yeast cells can leave wine cloudy, while active yeast may trigger further fermentation.


Pasteurization gives a kosher wine of the type called mevushal, literally "cooked" or "boiled", that can be handled by non-Jews and non-observant Jews without losing its kosher status.[12] 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 (95°C) for a few seconds, followed by rapid cooling.[13]

Other methods of stabilization[edit]


Premium wine production[edit]

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 Tom Stevenson note that they may improve wine quality when used with moderation and care, or diminish it when used to excess.[3] Winemakers deliberately leave more tartrates and phenolics in wines designed for long aging in bottle so that they are able to develop the aromatic compounds that constitute bouquet.[2] The consumers of some wines, such as red Bordeaux and Port, may expect to see tartrates and sediment after aging in bottle.[1]


  2. ^ a b Robinson, Janis (2006). Oxford Companion To Wine. Oxford University Press. ISBN 0198609906. 