What happens in the first weeks of a wine's life can be the most impactful on the finished outcome. Red wines are skin fermented which gives them their color and much of their complexity. To obtain maximum extraction, a winemaker will typically ferment red wines much warmer than white wines. The general temperature window for a red wine fermentation is around 75°F to 89°F. A wine fermented closer to the low end of this spectrum will be lighter in color, body, and tannin and will contain more fruity aromas while a warmer fermentation will yield bold flavors, rich color, and stronger tannin. Warmer fermentation temperature also increases the likelihood of fermenting completely dry. Many undesired microbes feed on sugar, so a bone dry wine with no residual sugar is at less risk of microbial spoilage during the later stages.
How Hot is Too Hot
One thing to note is that there is an upper limit to the fermentation temperature. At temperatures beyond 89°F, the wine can start to take on "cooked" tastes and lose the fresh fruit character that you would hope for. Very extreme temperatures can also stress the yeast and cause a stalled fermentation but up to 89° you should be fine. Be careful when adding yeast nutrient because it can cause rapid temperature spikes and push the wine warmer than expected.
What is "The Best" Temperature
This all depends on your personal preferences but many professional winemakers will say 85°-86°F is the sweet spot for a red wine during the primary fermentation. You may decide to go warmer or cooler based on several factors including grape varietal, whole cluster content, stylistic preference, etc.
Monitor fermentation temperatures frequently with a floating beer thermometer or a sanitized instant-read meat thermometer. Be careful because a strong fermentation will create some heat of its own. The amount of heat generated will depend on the size of the fermenter, ambient room temperature, strain of yeast, acidity, and yeast nutrition. Temps will spike the most in the first few days of fermentation.
The Perfect Temperature Profile
To take temperature control to the next level, you can begin to think about varying the temperature during the fermentation. One strategy is to start cool, and allow the yeast to get a slow natural start. Once fermentation has begun, ramp the temperature up rapidly to the low to mid 80s. At this point, there is very little alcohol in the wine, and water soluble compounds will be more likely to extract which include components of pigment and fruity esters. As the fermentation goes along, you can gradually decrease the temperature to reduce the extraction of alcohol soluble substances like harsh seed tannin. Cooling down to the low 70s will also help to drag out the fermentation and increase skin time and allow some time for tannins to soften before aging.
How to Control Fermentation Temperature at Home:
Take action to steer the must temperature towards your target. I like to wrap a seed heater around six gallon buckets to keep them warm. You can also use a space heater in the vicinity or get creative with infrared bulbs. There are inexpensive temperature controllers that can turn the heater on or off based on the wine temperature. They include a wired thermometer that is placed in the wine and the heating device is plugged into the outlet on the controller. These are very useful and help to reduce the risk of accidentally overheating the wine.
Keep track of your fermentation temperatures so that over time you can fine tune your winemaking style to your drinking preferences. It could be a year or more before you drink your wine so it is easy to forget what you did!
What About After Primary Fermentation?
As fermentation slows to a stop, slowly bring your temperatures back down and press the wine off the skins. If you are going to encourage malolactic fermentation, keep the wine in the 70°F to 73°F range until the slow malolactic bubbles come to a stop which could take a month or two. After Malolactic fermentation add sulfites to prevent spoilage and target closer to 60°F for the long aging period if possible.
What if I am Making Wine from a Kit or Juice Pail?
These are entirely different animals, as there are no skins or seeds to extract from. For kits or juice pails, I would recommend 70°-75°F. This is warm enough to encourage complete fermentation. Any warmer will not have much benefit and might kick off any bad microbes that may be hiding out in your juice pail.
Don't take fermentation temperatures for granted! The style of your finished wine is directly dependant on the temperature that it is fermented at. A few degrees either way can mean the difference between a fruity, light, easy drinking wine or a big, bold, ageworthy wine. It is up to you to decide what you want and steer your wine in that direction.
Read Next: Sweetening a Homemade Wine
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