The speed of a fermentation is a function of many different variables. Once you understand these variables you can manipulate them to slow down or speed up a fermentation.
Most wine makers agree that a slow fermentation is better. The thinking goes that the wine will hold on to more of the varietal characteristics as well as any delicate flavors and aromas created during fermentation. More aggressive fermentations tend to blow all varietal character out the airlock, so to speak.
Despite the stated benefits of a slow fermentation, there may be times when you need to speed things up. For instance, if your fermentation has been slowing down and you’re affraid it may become stuck, this would be a good time to get things moving again. Another possibility is some constraint on the winemaker’s time such as a trip or something.
With all of this in mind let’s explore the major factors that affect how fast wine ferments.
This is a pretty obvious driver of fermentation activity. As you know heat is a catalyst and when applied to a fermentation the yeast will ferment must more quickly. Cool the wine down and the rate of fermentation will also slow down.
There are, of course, limits to how far you can go both on the warmer and cooler sides of the spectrum. Temperature is something we’ve often discussed here at Winemaker’s Academy. Here are a couple related articles:
- The Effects of Fermentation Temperature on Wine
- How to Control Your Wine Fermentation Temperature – WMA009
Raising fermentation temperatures is decidedly easier than lowering it. Kurt recently shared a great method for controling fermentation temperatures you should probably check out.
To cool a wine you either need an ice bath or some sort of chiller (check out the podcast above for more information). Your best bet is to ferment your wine in a cool room (60-65 F / 15-18 C) and use a heating system as needed.
Yeast nutrients is an additive which provides nitrogen and ammonium phosphate. These help the yeast stay healthy and active. Much like you and I do better when we’re getting all the right vitamins and minerals so too does yeast do better with nitrogen and ammonium phosphate.
Nutrients are required for the yeast to do their job but they don’t make for a good catalyst for speeding up or slowing down a fermentation. I recommend using the amount specified in your wine making recipe, or if you’re not following a recipe 1 teaspoon of yeast nutrients (affiliate link) per gallon of must is what LD Carlson suggests.
According to professional winemaker John Garlich, yeast nutrients are like candy to yeast. They focus on eating that while it’s in abundance because it’s easier to process than sugar. However, when it runs out they can have trouble switching gears into consuming sugar. Listen to this interview with John for more information Wine Making Chemistry with Bookcliff Vineyards – WMA015.
I don’t recommend adding extra nutrients to speed up a fermentation nor should you reduce the nutrients to slow things down. I recommend adding an appropriate amount to ensure that the yeast is happy and healthy. If nutrient levels are too low the yeast will struggle and the fermentation may become stuck. So get the nutrient levels right whether you’re looking for a fast or slow fermentation.
Another similar product, yeast energizer (affiliate link), can be used to reinvigorate a sluggish or stuck fermentation. Again, I don’t know that I would use this on a wine that isn’t overly slow or on its way to being stuck but it can help ensure things move at a healthy pace.
Yeast strains vary in how aggressive they are in converting sugar into alcohol. Typically yeast strains sold as “Champagne Yeasts” or sparkling wine yeast tend to be quite aggressive. I have personal experience with EC-1118 and can attest that it is indeed very aggressive.
If you want things to move quickly pick an aggressive yeast. This in combination with the right temperature and nutrient level will result in making quick work of the sugar. On the other hand if you want to slow things down pick a less aggressive yeast and keep the temperatures a little lower and you should see a much longer fermentation time.
By in large there are not a lot of resources that I’ve found that will tell you which yeast strains are fast versus slow fermenters and because there are so many factors that affect the speed of a fermentation you should take recommendations with a grain of salt. It could be that a normally laid back yeast strain can get kicked into high gear in the right conditions or an aggressive strain that hits the brakes if something is not quite to its liking.
The volume of sugar the yeast needs to convert into alcohol is also going to be a factor in how long a wine takes to ferment. You can imagine that a must with enough sugar to produce an 11% ABV wine will finish much sooner than the same must with enough sugar to go up to 18% ABV.
Another aspect to sugar levels is the amount of alcohol being produced. Most yeast strains have an alcohol tolerance between 14-18%. If you’re using a yeast strain with an alcohol tolerance of 14% and your must has enough sugar to go up to 14% ABV your yeast may struggle to get that last 1-2% fermented.
It’s a good idea to make sure your yeast strain has a higher tolerance than the amount of sugar you have in your must. That way the yeast will not struggle to ferment the wine to dryness.
Aerate Your Must
Prior to adding pitching your yeast it’s a good idea to stir some oxygen into your must. Oxygen helps yeast reproduce and build up a population large enough to handle the entire fermentation process. Episode 3 of the Winemaker’s Academy Podcast was all about the yeast life cycle. The quicker the yeast builds their population the more quickly they’ll ferment your must.
Once fermentation has begun though I don’t recommend aerating the must. Additional oxygen can cause oxidation. Aeration during fermentation is a widely debated topic though so use your best judgement here.