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Cold soaking or cold maceration is a winemaking technique where crushed wine grapes are allowed to macerate in contact with the grape skins prior to the start of fermentation. This is different from the regular course of maceration where, most notably, red grapes leach tannin, color and flavor phenolic compounds from the skins, seeds and stems during and after fermentation in that cold soaking takes place when the must is largely an aqueous (water-based) solution versus a water and ethanol solution that wine becomes once yeast are introduced.

As some compounds, such as the anthocyanins that contribute to color from the grape skins, are more soluble in water while others, such as the harsher tannins from the seeds, are more soluble in alcohols, some winemakers believe this technique allows them to draw out more color and aromatics into the wine with softer tannins. However, the scientific data on the effectiveness of this technique has been mixed. While the practice has many proponents, particularly among Pinot noir winemakers, the practice also has a far amount of skeptics.

In order to prevent spontaneous or "wild ferments" from taking place, winemakers will chill the must to around 4°C (39°F) or lower (hence the "cold" in the maceration) and will often add sulfur dioxide (between 25 to 75 ppm or 25-75 mg/l) to keep microorganism at bay. Some winemakers will often do various cap management techniques like punch downs or pump overs to not only aerate the must but to encourage further extraction of anthocyanins and phenolics from the cap of grape skins that form as the juice settles in tanks.

History and global use

While the term "cold soaking" and the deliberate use of the practice is relatively recent, oenology experts such as Roger Boulton of the UC Davis Department of Viticulture and Enology notes that its origins are found in the traditional winemaking techniques of Burgundy before modern inventions such as inoculated yeast cultures and temperature controlled tanks were adapted. Here in the cool continental climate of eastern France, the temperatures around harvest would often be too low for the freshly crushed must to quickly begin fermentation. As the must sat in the cellars, slowly warming up and giving the native micro flora time to begin fermentation, it would essentially be "cold soaking" for several days or even weeks before fermentation kicked in.

Lebanese oenologist Guy Accad is credited with renewing interest in cold soaking as a modern winemaking technique with his work as a consultant in Burgundy during the 1970s and 1980s. Accad advocated letting the freshly crushed grapes soak for 2 to 3 days prior to the start of fermentation in must that has been highly sulfured to not only prevent premature fermentation but also to enhance extraction of color and tannins compounds.

In the late 20th and early 21st century, cold soaking became particularly popular among Pinot noir producers in California and Oregon.

What maceration does

The term "maceration" comes from the Latin word maceratus which means "to steep" and refers to the separation or softening of materials in a liquid solution that allows the extraction of other compounds. In winemaking, this technique is the principle point that distinguishes red winemaking from that of white winemaking. The pulp or pericarp of all wine grapes (with the exception of red-fleshed teinturiers) from Cabernet Sauvignon to Riesling produces pale grey to virtually colorless juice with very little phenolic compounds that contribute to the flavors, mouthfeel and tannins associated with red wine. It is the skin, seeds and stem (particularly the hypodermis layer of the skin) that these compounds are found and it is only through the process of maceration, where the crushed grape must spends time in contact with the skins, that these compounds get "steeped" out and extracted into the wine.

Wine grapes destined for white wine production (including Pinot noir used in blanc de noirs) are often pressed quickly after harvest with skins being separated from the juice to avoid the extraction of color and phenolics. There are some exceptions (such with some Chardonnay, Sauvignon blanc and Sémillon as well as the production of orange wine) but this period of skin contact is usually very brief, from a few hours to little more than a day, and tends to produce a style of wine that is more full bodied and can be more bitter than other whites.

The maceration process is dependent on the skin of grapes first being slightly broken (or crushed) in order to release some juice and allow access to the pulp and inner skin layers. In this respect, maceration is different from the winemaking process known as carbonic maceration typically associated with the French wines of the Beaujalois region. That process, while called maceration, could be more accurately described as a whole cluster fermentation where the grapes undergoes chemical changes inside each individual berry.

The factors that influence the maceration process include the temperature of the must, the surface to volume ratio of the fermentation/storage vessel, the length of time that the must spends in contact with the skins, the amount of agitation or break up of the floating cap of skins that forms and the composition of the must (more aqueous versus a water/ethanol mixture later in fermentation). Higher temperatures and alcohol levels tend to encourage more extraction, more quickly while cooler temperatures and a more aqueous solution tend to promote a slower extraction rate.

In general, the compounds responsible for color in wine, namely anthocyanins but also some tannin compounds like catechins and proanthocyanidins that react with the anthocyanins to form polymeric pigments, are extracted from the grape skins early in the winemaking process when the must is mostly an aqueous solution with very little alcohol. According to Burgundian oenologist Louis Ferré in his 1958 work Traité d'oenologie bourguignonne, after six days of maceration nearly all of the available color components from the skins have been extracted.

Benefits

Among the benefits most commonly cited for cold soaking is the belief that, in the absence of alcohol, anthocyanins extracted from the skins will form color stabilizing bonds with with other phenolic compounds before more bitter tannic compounds are extracted. This may give the winemaker an opportunity to have a shorter, overall maceration period and press the grapes earlier. Wines that are pressed before complete dryness (often called "short vatted") tend to be lighter in body, fruitier, less astringent, with more floral aromatics and able to be consumed earlier. The tannins that do get extracted in the resulting wine after cold soaking are often described as "finer, more mouth-friendly".

This can also be an advantage with certain grape varieties, such as Pinot noir, that have a tendency to complete fermentation very quickly (sometimes overnight with certain yeast strains and conditions). With these "fast ferments", the period of aqueous maceration can be very short and some winemakers utilize cold soaking as a way to extend and slow down the overall fermentation process.

In regards to the purported aromatic differences between wines that are cold soaked versus wines that are not, anecdotal reports from winemakers vary. Ted Edwards from the California winery Freemark Abbey describe more "bright fruit" notes while Karen Steinwachs of the Santa Ynez Valley winery Buttonwood Farm says that Pinot noirs that have been cold soak tend to have a characteristic blueberry note that shows up more than in Pinots that have gone through conventional maceration. Julie Lumgair, winemaker of the Russian River winery Windsor Oak Vineyards, notes that if the wines are bottled early (less than a year from vintage) some of the aromatics derived from cold soaking will stay with the wine after bottling.

While many of the sensory benefits associated with cold soaking are difficult to quantify, one acknowledge benefit that can be is potentially more trustworthy readings on certain laboratory measurements (Brix, pH and titratable acidity) taken on the grapes after a few days cold soaking. Typically wineries take these initial numbers soon after the grapes are harvested and crushed before alcohol fermentation begins. These initial numbers may be skewed if the tank of must is not thoroughly mixed and homogenized. The presence of raisin berries and slightly dehydrated fruit can make initial sugar readings seem lower than they actually are before the raisin release some of these sugars. Additionally, potassium ions gets leached from the skins soon after harvest and could lead to more elevated pH levels than originally measured. Cold soak advocates note that the process of cold soaking, which often involves thorough mixing of the must, gives wineries the opportunity to take lab measurements a day or two after crushing with the numbers being more reflective of what is actually in the must before the chemical reactions in alcohol fermentation take place.

Disadvantages and questions about the practice

One of the primary disadvantages involves the potential for spontaneous fermentation to begin with non-Saccharomyces cerevisiae yeast, such as species from the Kloeckera genus which are likely to dominate the micro-flora in the vineyard and still be present on the freshly harvested grapes. Even with cold temperatures and sulfiting the must, as many cold soak practitioners do, the possibility of relatively sulfur resistant genus such as Brettanomyces, taking over the fermentation and causing off-flavors in the wine is still possible.

Some winemakers question if the benefits touted with cold soaking are actually advantageous with winemaker Lane Tanner, a specialist in California Pinot noir, noting that Pinot noir, itself, is a very thin skin variety without much color pigment to begin with and the process of regular maceration tends to extract all available color anyways. Sentiments like this has lead some wine journalists, such as Tim Patterson of Wines & Vines magazine to wonder if with cold soaking: "Do you get more stuff or just get it earlier?" The lack of conclusive scientific research demonstrating the benefits of cold soaking has also lead to skepticism about the practice.

With white wine grapes

While most white wine grapes are pressed almost immediately after harvest, with some varieties (such as Chardonnay and Sauvignon blanc) some winemakers will allow for a period of brief skin contact prior to fermentation. This method, known as macération pelliculaire in French, is often done essentially as a "cold soak" with the crushed grape must being brought down to low temperatures (often 0°C/32°F) and sulfited to protect against spontaneous fermentation and microbial spoilage. The low temperatures and aqueous nature of the pre-fermentation must also helps minimize the extraction of bitter phenolic compounds that consumers often do not enjoy in white wines. The length of cold soaking will vary from winemaker but for most white grapes it ranges from a few hours to a little over a day.