Heat is a catalyst. By definition when it is applied to a chemical reaction or biological process it speeds things up. The same is true for fermentation.
The higher your fermentation temperature the faster your yeast will convert sugars into alcohol and carbon dioxide. While this sounds great on the surface you never really want to rush anything when it comes to making wine.
Warm fermentations can lack character as well as any terroir you might be hoping to capture in your finished wine. Cooler fermentation temperatures help preserve the uniqueness of your specific fruit and helps the character and terroir shine through. For better or worse cool fermentations take longer to complete.
Ideal Wine Fermentation Temperature Ranges
According to yeast producer Wyeast red wines should be fermented between 70 and 85 degrees F (20-30 degrees C). You’ll get better color and tannin extraction at the higher end of this spectrum.
In this temperature range fruity flavors and aromas don’t get preserved which can be good for a red wine. When fermentation temperatures that approach 90 degrees F though you can run into cooked flavors.
White wine fermentation temperatures should be between 45 and 60 degrees F (7-16 degrees C). These lower temperatures help preserve fruitiness and volatile aromatics, characteristics more in line with a white wine.
White wine fermentations take longer. Academy member Rob ferments his white wines at 45 – 50 degrees and they can take up to a couple months to complete.
Going beyond ideal fermentation temperatures can cause problems. Ferment too hot or too cold and your wine will suffer.
Fermentations that get too hot not only ferment too fast but it could lead to “cooked” flavors. Your wine will taste like it was boiled on the stove. Additionally, yeast can only tolerate fermentation temperatures that are so high. Go beyond their maximum temperature tolerance and they’ll die.
Keep in mind that the fermentation process is exothermic which means that heat is produced as the yeast are doing their work. So even if your wine is stored where the room temperature is within the ideal temperature range your wine could still over get over heated.
At the other extreme if your wine gets too cold your yeast will go dormant. The good news here is that when your fermentation temperature rises again the yeast will likely wake up again and continue fermenting. Even if they don’t come back you can pitch more yeast and continue where you left off. Your wine won’t get damaged by excessively cold temperatures like it will with excessively warm temperatures.
Measuring Fermentation Temperatures
The simplest way to monitor your fermentation temperature is to use a sanitized kitchen thermometer. Just open up your fermentation vessel and take a measurement. Be sure to work as quickly as you can to limit the amount of time your wine is exposed to oxygen.
Another option is to get a self adhesive temperature strip. It sticks right to the side of your carboy or fermenter and displays the internal temperature. While these aren’t accurate to the tenth of a degree or anything they will at least give you a good idea of where you are in the temperature range.
Heating Your Wine
There are several inexpensive products to help you warm up your wine when fermenting in a cool environment. The least expensive option is using an insulative wrap on your carboy. These are passive and only trap heat produced by fermentation.
Another option is to use a heating belt or a ferm wrap. These are electric heaters that wrap around your carboy or fermenter. Once plugged in they will raise the temperature of your wine by approximately 10 degrees F.
To get finer control of how warm your wine is you can pick up a thermostat which allows you to dial in the temperature to within a degree of what you set it at. Heating bands usually run around $20 and the thermostat is another $80.
Another similar device is a heating panel. These products are just a flat pad that you place your carboy on top of. When plugged in they heat up to a pre-determined temperature. Again, you can pick up thermostats for these too.
Cooling Your Wine
The easiest way to bring down a high fermentation temperature is to place the fermenter or carboy in an ice bath. Simply place your container in a plastic tub, add cool water, and then add ice. Be very careful when moving your carboys especially if they’re wet. Remember, if you go too far your fermentation can stop.
Wine cooling equipment can be quite expensive. There are a few products on the market to help you with this task, however, most solutions cost well over $1000.
Beyond using ice water you could opt for a glycol chiller to use on the wine itself or you can cool the entire room. The latter may not be practical if you don’t have a thermally isolated room to ferment your wine in. Glycol chillers start at around $1600 and go up from there. They’re designed to work on larger fermentation tanks.
One intermediate option is to pick up a stainless steel tubing coil or heat exchanger used in glycol chiller system and run cold water through it. This works a little more slowly and you’ll have to figure out your own system of recirculating the cold water or find a garden to pump it into. Coils start at around $300.
Monitoring temperature and maintaining ideal temperature ranges is a very important part of making a great wine. Excesses above or below the ideal range will have a direct impact on your finished wine, including whether or not it finishes at all.
Keeping your wine in the house is often the best option for the amateur wine maker as we tend to keep our homes within the ideal temperature ranges listed above. Small adjustments may be necessary but luckily the methods for making those small adjustments are doable.
Photograph of Blue Thermometer by: Sam Catch