By: Gerald Dlubala
Temperature control and consistency are magic words to a winemaker. From planting through harvest, packaging and storage, the winemaking process is vulnerable to temperature instability or fluctuation. With each growing season bringing the potential for unique challenges regarding those temperature fluctuations, the winemaker must be prepared to react to situations as they occur and protect their product under all conditions.
Providing stable and consistent temperatures and humidity levels brings that protection and allows the wine to retain freshness, flavor and predictability. For bottled wines, humidity fluctuations can cause problems, including shrinking corks, mold and contamination.
The ideal temperature for storing grapevines to inhibit active growth yet keep the stock viable until conditions are suitable for planting is between 34 to 36 degrees Fahrenheit (1-2 C). After harvest, when bringing the grapes in for processing, it’s unknown what the current weather and ambient temperatures will be until they are upon you. If too warm, best practices advise a cool-down period before pressing, after pressing, or both, depending on the variety and type of fermentation used. If that’s not possible, it may be advisable to store grapes in a temperature-controlled facility until ready for processing.
Refrigeration Capabilities are Necessary for Quality Wine Production
Carolyn A. Warnebold is the majority owner of OakGlenn Winery, located in historic Hermann, Missouri. OakGlenn Winery produces about 400 gallons of their popular Norton variety from an original vine stock planted in 1859. Other wines offered onsite are grown and processed at separate locations.
“There is no doubt that without a good refrigeration system, you’re not going to achieve good wine,” said Warnebold. “Our grapes go through crush immediately after harvesting and are then placed in fermentation tanks for 24 hours before adding the fermentation ingredients. During fermentation, the must has to remain at 70 F. Our chilling equipment runs a glycol and water solution at 65 F through jacketed tanks to control the cold fermentation of the must.
After a 10-to-14-day fermentation, we press, tank and hold the juice and grapes at 65 F until the fermentation and settling process is complete. The juice/wine is then racked after two months, placed in another tank where the wine rests at 32 F. Two weeks before bottling our wines, we drop the temperature to 22 F to drop any further tartrates. Our wine is then filtered immediately before the bottling process and is usually ready after six months.
We process our white wines and blends similarly, except for the fermentation, which is done with juice only. We do not perform any further barrel aging of our wines. We hold our bottled wines in our tasting and sales rooms at a consistent 45 F.”
All of the tanks at OakGlenn Winery use the same glycol and water chilling system to control temperatures and guarantee consistency, including their cased wine warehouse. According to Warnebold, glycol chillers are much more cost-effective than other types of systems on the market.
Cold Storage Essential to the Flow of Quality Winemaking
Chris Graves is the winemaker at Naumes Family Vineyards, operating Naumes Crush and Fermentation LLC as an outsourcing option for wineries. He told The Grapevine Magazine that cold storage capability is an essential tool for the winemaker, not only for proper fermentation but also for allowing a winemaker to buy time and provide improved processing and cold soaks.
Additionally, if a winery uses large tanks, chillers are essential in controlling overheating and any corresponding sticking issues in the tank. When fermenting rosés or lighter wines, longer fermentation times are needed to develop the aromatics, so temperature control is even more critical.
“While grapes are still on the vine, they are naturally protected from microbes like bacteria and yeast,” said Graves. “But once harvested, that natural protection is compromised, and exposure begins.
When the vineyard is at its busiest time of year, meaning harvest, getting those freshly picked grapes delivered to the winery for processing and into the fermentation vessel within an acceptable temperature range can be tricky. Additionally, grape varieties’ sugar levels and freezing points differ after harvest, so it’s important to control and maintain proper temperatures as conditions change. If that’s not possible, then offsite cold storage options become a winemaker’s best friend.
Grapes handle the sorting and destemming process better when cold and dense, especially in quality reds that demand more fruitiness and less tannin extraction. Most often in red winemaking, the winemaker will want to keep the must in fermentation vat cold for a cold soak before fermentation.”
That’s where facilities like Naumes Crush and Fermentation can help the vineyards produce quality wine, offering cold storage options and space for wineries to store their grapes at the preferred 33 F directly after harvest.
“It can be anything that causes a need for cold storage that some smaller craft wineries just don’t have,” said Graves. “It might be a weather event that causes a mass fruit pick from the vines, something unplanned that changes a vineyard’s scheduled harvest plans or even complications with vineyard equipment that causes harvest issues and throws off schedules and deadlines. Wineries can buy time if they need to pick grapes but aren’t ready to process just yet. Plus, with the time to plan the process, information flows better, making the process more accurate and consistent with higher quality and better results. It’s just easier to have and stay on schedule. Utilizing offsite cold storage like ours assures a winemaker that their product is held and processed correctly, if needed, by knowledgeable and experienced staff and winemakers. It ultimately results in higher quality wines and better, more efficient logistical flow.”
Most wineries use standard glycol chillers because of the benefits that come with them. First, they put less stress on pumping equipment because the glycol mixture has built-in lubricating properties.
Second, glycol chillers have a lower freezing point, allowing lower operating temperatures without concern over system freezing and damaging the unit.
Finally, since glycol chillers allow better holding temperatures, they help minimize heat pickup on delivery and return. Heat pickup tends to be more of an issue in higher volume production facilities that use more piping in their production.
Smaller operations can use mobile heating and cooling units. They offer the convenience of portability to use when and where needed, but that convenience generally means limited capability compared to a more extensive plumbed system.
Graves recommends a plumbed system when a winery reaches the one to two thousand cases produced rate, if nothing else, because of the benefits of a more extensive, built-in system. For example, a plumbed system allows a wider variety of wine to be produced onsite because of the availability of the unit to provide heating and cooling, essential in remaining consistent in critical times of fermentation and wine storage.
“The best recommendation I can give someone looking at refrigeration and cold storage is to use a plumbed and closed glycol system, and make sure to buy one that is oversized for your current production needs,” said Graves. “I see a lot of wineries that purchase and install a system to fit their immediate needs, and then when they start to increase production or grape/wine variety or have a great production year, that system is already undersized for their needs.”
One of the biggest issues we see in wineries just starting out or in the small established craft wineries. If you have any thoughts or desires to increase production, move into new varietals or even do something different in the future, purchase and install a refrigeration or cold storage system that is oversized in the beginning so that you can grow into it seamlessly as a winemaker.
Get a quality plumbed system that also uses quality pipes and fittings to handle extreme temperatures and varying pressures that occur in winemaking.”
Graves also recommends that winemakers use quality temperature controllers, like TankNet, and match them with reliable software systems that connect with a cloud-based network, allowing the controllers to be accessed and used with smartphones or other remote-control devices to instantly address any problems or concerns and help maintain process consistency and integrity.
“You know, consistency is everything, and consistent temperature control is the key to producing a bottle of quality wine. Wines don’t tolerate fluctuating temperatures, so if you can do it yourself, do it, but if for any reason you can’t, it’s worth it to have an offsite company handle your storage, crush and fermentation needs. Naumes offers the full spectrum of post-harvest services, from grape to bottle, including lab work, analysis and more.
Recommended Temperature Guidelines
Temperature fluctuations can have a detrimental effect on bottled wines, which react to heat by aging faster. In addition, direct sunlight or artificial light can react with phenolic compounds in the wine and cause spoilage. Lighter-colored wines are more susceptible and therefore more apt to be packaged in tinted bottles.
Wines undergoing malolactic fermentation are generally held at 68 to 75 F (20-24 C). Barrel storage rooms require constant temps around 55 to 60 F (13-16 C). Clarification processes like fining, centrifuging and filtering needs temperatures in the range of 32 to 77 F (0-25 C). Hold sparkling wine at temperatures below 54 F (12 C) to promote the required carbonation, and when bottling wine, temperature recommendations are typically around 60 F (15 C) to discourage or limit dissolved oxygen during the filling process.
Optimal wine storage has traditionally been listed at 55 F (13 C), but according to winemakers, red varietals can safely be stored between 53 to 66 F (12-19 C). You can go a little cooler with champagnes because of their needs–50 to 59 F (10-15 C). Wine should never be frozen or stored for a length of time above 68 F (20 C).