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.

Fermentation Temperature

Increasing wine fermentation temperatures can speed up the process.

Warm wine ferments faster.

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:

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.

Nutrient Levels

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 Aggressiveness

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.

Sugar Levels

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.

Photograph by: Tim Patterson (license)

  • Stephen Boland

    This is a great article, thanks!

    I have been finding it beneficial to work with a specific yeast strain over and over in different conditions and with different varieties of wines. I have been doing this only because all my wine kits have included Lalvin EC-1118, but I am learning a lot about how this yeast works because of this repetition and from fermenting it at different temperatures. I feel that by knowing the temperature and alcohol limits of specific yeast strains through practice and also what the changing conditions of fermentation do to the aroma and flavor characteristics of the yeast in the wine can be a great help to us as winemakers.

    One practice that is common with mead makers when dealing with yeast nutrients is to decide how much of the nutrient you need for the complete fermentation, but to stagger the additions. For example, you might add 1/3 of the nutrient up front, 1/3 when specific gravity falls to 1.XXX and the rest after your must ferments down even more. This, in theory, keeps the yeast active enough to deal with the sugars, but does not allow them to become too reliant on the extra nutrients. I am now wondering if this might be a reasonable practice with wine making.

    • I think that’s very wise to choose a yeast strain and get to know it. This is the same method I hear professionals using in order to make the best wines possible on a consistent basis.

      Staggering yeast nutrients is a great idea! Again something I’ve heard from several pros to keep a fermentation moving.

      Thanks for sharing! -Matt

    • I’ve never tried it with wine, but when I started routinely using staggered nutrient additions in mead, it improved my results immensely and helped keep fermentations going even as I pushed the temperature down to the low end of the recommended range for the yeast in question. I imagine wine must is a bit more nutrient-dense than honey must, however, so I imagine the nutrient needed might be different.

      Another thing that improved my mead relates to your comment as well–tailoring the OG of the must to the alcohol tolerance of the yeast strain to end up with the right amount of residual sugar and sweetness without having to backsweeten. I use 71B a lot, and while it’s supposed to have a tolerance of 14%, I’ve routinely pushed it to 15.5% or so, so…practice and environmental conditions do matter.

      • Wine must is much more nutrient dense from my understanding. Honey is largely a sugar solution. The nutrients required are likely similar though the volume needed I imagine would be different.

        -Matt

  • What about degassing? Does that affect fermentation speed?

    I’ve recently adopted the practice of degassing mead multiple times during initial fermentation after learning that several of the award-winning meadmakers do this. I haven’t isolated its effects, however, because I also adopted other practices (colder fermentation, staggered nutrient additions) at the same time.

    From what I’ve read about degassing wine, it seems like it is generally done only once, after fermentation is complete.

    • I think that degassing can certainly help keep a slow fermentation moving. This is something commonly recommended for mead fermentations.

      When I make mead I usually make in 1 gallon jugs. Once every two days or so I’ll pick up the jug and give it a swirl. That seems to get the airlock going. You can have too much suspended CO2 which gives the yeast trouble. Anything to reduce stress on the yeast is usually worthwhile.

      Thanks for pointing this out Dan.

      -Matt

      • I tend to make 5 gallon batches and use a stirring attachment on a drill to mix and aerate the must in the beginning and then to degas later during fermentation.

        It’s very effective at both, but I have to be careful when degassing because it’s easy to degas too aggressively and bring CO2 out of solution very fast, at which point some of the must bubbles out of the fermenter and creates a giant mess.

        I’ve made this mistake a number of times, including recently. One day I’ll learn…