Sometimes when you read a tasting note or hear a winemaker describe how a particular wine is made they’ll make comments like, “Cold fermented, or fermented at warm temperatures”. You may wonder, why are they telling me this? Here’s the deal with the temperature of fermentation.

Sometimes when you read a tasting note or hear a winemaker describe how a particular wine is made they’ll make comments like, “Cold fermented, or fermented at warm temperatures”. You may wonder, why are they telling me this? What does this mean? How does it affect the wine, and why does this matter to me? Here’s the deal with the temperature of fermentation.

First you need to understand the process of fermentation. It’s the process where tiny little bugs (yeast) eat the natural sugars in grape juice and produce alcohol and carbon dioxide (CO2). In other words it is the process of turning grape juice into an alcoholic wine. There are lots of topics we can discuss in fermentation (yeast type, primary/secondary, nutrients, sulfites and more) but for this article we’ll just focus on temperature and time. In terms of temperature the wine industry roughly defines fermentation temperature in these ranges:

Cold 48-55°F
Cool 55-70°F
Warm 70-85°F
Hot 85-90°F

By way of analogy let’s talk about a process that we all know well, namely making chocolate milk or hot cocoa. When making chocolate milk we’ve all noticed that the stirring process of turning milk into chocolate milk takes much longer when the milk is cold. If the milk is too cold we may never get a tasty beverage as the chocolate never completely mixes in. The common is solution is to warm the liquid just enough to get the desired result, i.e. a well-blended cold chocolate milk. On the hot chocolate side the challenge is managing heating of the milk because if it gets too hot the milk boils over and burns producing a nasty mess. So, to produce our particular yummy drink we must closely monitor the temperature to achieve the desired results. The process is similar in wine making.

In the making of white wines we want the temperature to be warm enough to allow the fermentation occur but not so warm that it happens too fast where the flavors never have a chance to develop. So, with wines like Pinot Gris we will cold ferment in stainless steel slowly for months as our goal is to preserve the fruit forward aromas and keep a light mouth feel with crispness. Chardonnay on the other hand is done at cool temperatures for up to a month so that we can extract more color, texture and complexity from the lees. (lees: A heavy sediment consisting of dead yeast cells and other solid matter such as grape pulp, pips and so on.) Chardonnay is often oak barrel fermented to add complexity and develop flavors like coconut, butterscotch etc. which are extracted from the barrel.

As we move on to the production of red wines the fermentation temperature rises as the process itself occurs in the midst of skins. With red wines we’re aiming to have more extraction of color, flavors and tannins from the must (must: mixture of fermenting grape juice, pips, skins, stalks and so on) so we’ll generally ferment in the 75-85 degree range. Sometimes we go a bit cooler when making wines with lighter color and fruitier character like Pinot Noir. With Meritage varietals (Cabernet, Merlot, Petit Verdot, Malbec) or Big Italian Reds (Nebbiolo, Barbara) temperatures will range from warm to hot and fermentation times can be as short as 10-14 days. In these big earthy wines we’re looking for deep color and mature tannins to balance the fruit and create a more refined wine. These wines are almost always open tank fermented before being pressed and put into barrels.

There is another range of heat (extreme that goes above 90 degrees) and though it may be quicker (as little as two days) you risk the chance of a dead or stuck fermentation if things get too hot and kill the yeast. Even if you don’t kill the yeast you’ve assuredly add a madeirized character that’s better off in some grocery store cooking wine (salt added) than anything you’d want to drink in a glass.