Cold Settling, Cold Soak, and Cold Stabilization: The Difference Between the Three
Making wine is no easy task and many variables are at play that determine the difference between a quaffer and a gem. Among the most overlooked stages of the winemaking process are the critical steps that take place immediately before and after fermentation. Two of the most common of these steps are the cold soak and cold settling. Both of these occur prior to fermentation. If one or both are ignored, the odds will be slim that the finished product will be considered commercially acceptable. But what is the difference between these two similar-sounding processes? Well, one is more common in the production of white wines and rosés where the other is more commonly used in the production of red wines.
The “cold settling” step involves letting the grape must (pressed juice, skins, and sometimes stems) settle overnight in a vat for up to three days wherein the solids sink to the bottom. Typical temperatures for this process are between 41-50 degrees fahrenheit (5-10 Celcius). Sometimes commercially available enzymes called pectolytic enzymes are added to the must to break down pectin, a component of plant cell walls that functions to hold the unwanted particles together. The purpose of this step is to clarify the juice to prevent off-flavors from being present in the final product. Once the suspended particles have settled, the clear juice is transferred, or racked to another vat or fermentation vessel. This is really only used for the production of whites and rosés.
The “cold soak” is done at temperatures falling within the same range for the cold settling step, but the aim of this practice is to extract flavor and color from the must rather than clarify the juice of suspended particles. This is the main difference between the two as color extraction more commonly leads to the production of red wines. This step will continue into fermentation where the skins are left in contact with the fermenting juice promoting further extraction. Though both of these steps are risky as volatile acid-producing bacteria are largely unchecked, the benefits of this process far outweigh the risk and keeping the must at low enough temperatures should discourage any off flavor-producing bacteria from having a large impact.
So that leaves “cold stabilization”. This process is actually post-fermentation and its main aim is to prevent the forming of crystalline precipitate in the finished product upon chilling the wine. If this step is ignored crystals will form when the wine is chilled which resemble shards of glass. These are harmless to the consumer but are generally recognized as a flaw in finished wine. In order to prevent this unwanted precipitation, finished wine is chilled at temperatures below freezing for up to several weeks allowing the crystalline precipitate Potassium Acid Tartrate (KHT) to form. Once these crystals are formed the wine is then racked into new bottles leaving the crystals behind. These new bottles can be chilled and no crystals will be present providing a commercially acceptable finished product. All three of the aforementioned concepts are commonly misunderstood, but each one is unique and serves a critical role in wine production.