Chilling Out with a Nice Wine
The right chiller can provide winemakers with an efficient tool to optimize the temperature control portion of the winemaking process.
Certainly, the production of wine is a complicated mixture of art and science. Color, flavor and aroma -- characteristics that define a quality wine -- rely as much on the technical expertise and experience of the winemaker as on the grapes themselves.
Precise process temperature control is one of the most critical technical requirements of modern winemaking. It allows high-volume production while ensuring that the unique character of the final product is consistently attained. Temperature control also is an important factor in the preservation of wine to ensure the consistent quality required to allow distribution in today’s global market. Chillers can provide the winemaker with that control.
Particularly at two points in the pre-fermentation stage of winemaking, chillers have proved effective. First, during a process called crio-maceration, the grape musts -- freshly pressed grapes containing solids such as pulp, skins, stems and seeds -- are cooled to a temperature of 40°F (4°C) in stainless steel tube-in-tube heat exchangers. The time and the temperature at which this process takes place greatly determine the characteristics of the finished product. Second, cooling plays a critical role in the clarification process. This pre-fermentation process involves static separation of the musts at a temperature of 50 to 58°F (10 to 14°C) to remove suspended impurities.
During the fermentation process, temperature control, in the form of heating and cooling, is essential. For instance, temperature control of the musts is required for the production of high quality wines. Alcoholic fermentation is the chemical reaction in which yeast is used to transform the natural sugars of the fruit into alcohol. The heat generated by this exothermic reaction has to be managed. If must temperatures are allowed to reach the 85 to 105°F (29 to 40°C) range, the reaction will be stopped. This results in high sugar content and an unstable product that requires the addition of sulfur dioxide (SO2) to allow it to be stored without spoiling. In general, optimal fermentation temperatures are 65 and 68°F (18 and 20°C) for white wines and 77°F (25°C) for red wines.
Although fermentation tanks generally are cooled, certain system features may require heating as well. In these cases, a heat pump version of a standard chiller can help meet this requirement. Stainless steel casing panels make the chiller more hygienic and help increase overall durability. Some chillers have an extended surface evaporator located inside the storage tank that provides high cooling efficiency and low resistance to water flow.
As an example, consider a winery with an annual production of 500 tons, which uses a chiller to manage the 18 tons of cooling associated with the fermenting process. The chiller’s on-board storage tank maintains a 90-gal supply of chilled water at 41°F (5°C), from which it is pumped through heat exchangers immersed in the fermentation tanks (or in some cases, through tank jackets). The large volume of the chiller’s storage tank provides a thermal mass that compensates for sudden changes in cooling load to provide constant chilled water temperatures regardless of external conditions.
Malic acid occurs naturally in wine and provides a tart, apple-flavored taste. For the wine to have a more delicate taste, malolactic fermentation is employed by adding lactic acid bacteria to the wine to convert the malic acid to the softer-tasting lactic acid. This often is used for barrel-aged (oaked) wines.
At times though, malolactic fermentation can occur unintentionally after bottling, resulting in a slightly carbonated and bad-tasting wine. This can be avoided by raising the wine temperature to about 77°F (25°C). Either a customized heat pump chiller or a chiller that is equipped with condenser heat recovery can provide the heat required for this process.
At low temperatures, potassium bitartrate, a natural component of the wine, will appear as sediment in the bottle. To avoid this situation the wine is chilled to about 27°F (-3°C) for a period of up to 24 hours prior to bottling. This process, called cold stabilization, causes the potassium bitartrate to precipitate out of the wine, where it can be filtered out. At the example winery mentioned earlier, cold stabilization can be achieved with four 10-ton chillers that chill brine to about 19°F (-7°C). This brine then is circulated to the exchangers or jackets in or on the wine tanks to maintain the proper temperature.
In conclusion, winemaking is delicate business. Each phase of the process requires controlled conditions to achieve optimum quality. The winemaker must have complete control of process temperatures and be informed of any problems. In order to have this level of control, it is important that winemakers seek process chillers that include features such as digital temperature controls, digital temperature indication, ease of parameter adjustment and built-in alarms. Remote monitoring and control, and a supervisor system also are helpful. Another option is to equip the chiller with a server card that can communicate with a remote PC. This type of web-based server transmits performance data and allows remote operation via an Internet browser interface.