Fermentation is crucial to the brewing process. Homebrewers eager to drink their homemade beer want to know how long to expect to wait for fermentation to start.
Fermentation can start anywhere from 3 to 24 hours after introducing yeast to wort. You can accelerate fermentation with certain yeast strains, by using a starter, using elevated temperatures, and aeration. You’ll know fermentation has started when bubbles form on the surface.
All of these variables play into the fermentation timeline. Continue reading to learn more about the various factors that stimulate fermentation and dictate when fermentation begins.
How long until homebrew beer starts fermenting?
Fermentation is the key to turning simple ingredients — water, grain mash, and yeast — into delicious, homebrewed beer! The yeast converts sugars in the grain mash and water mixture (otherwise known as wort) into ethanol and carbon dioxide.
While the process itself takes a few days before reaching peak alcohol and carbonation, getting started is often a pretty fast process and can typically be noticed between 3-24 hours after pitching the yeast.
Yeast is a microorganism, and it is going to work quickly and efficiently to feed itself in this environment you have created as a homebrewer.
There are a handful of reasons why there’s that three-to-twenty-four-hour window, and the majority of them boil down to the fact that yeast is a living organism and therefore has different needs depending on its circumstances. These factors include:
- Different yeast strains: Each strain has a specific purpose and for some of them, that purpose could be to very quickly start fermentation. Likewise, other strains are reserved for slower fermentation.
- Using a yeast starter: A yeast starter is already tempered, meaning it is ready to absorb nutrients, multiply, and convert sugar into alcohol and carbonation by the time it is pitched into wort.
- Wort temperature: The ideal temperature for wort depends on the kind of beer you are making. Ales can withstand higher temperatures whereas lagers require a cooler temperature. Consult the yeast’s packaging to find the preferred range.
- Ambient temperature: Higher temperatures encourage yeast activity, but going too high could kill yeast. Too low and it goes dormant. Yeast tends to prefer room temperature (68-72℉) but again, check the packaging for guidance.
- Aeration: While yeast doesn’t require oxygen, incorporating oxygen into the batch helps yeast multiply faster and healthier through a process called biosynthesis.
- Yeast-to-sugar ratio: A higher concentration of yeast to sugar can speed up fermentation because all the sugar available to the yeast will be consumed much more quickly. Underpitching your yeast, on the other hand, will delay fermentation.
Any one of these variables, or combinations therein, can accelerate fermentation.
Certain yeast strains ferment faster
Different yeast strains bring different qualities to your beer, and one of those could include a faster initial fermentation. Yeast is really what defines the beer; yes, you can add all sorts of flavors, decide to rest it for an extended period of time in bourbon or wine barrels, or experiment with various kinds of hops, but the type of yeast you use is really what really makes your beer.
And not just literally — without yeast to convert the sugars of the grain mash into alcohol and carbonation, you’re left with a wort that’s fairly unappetizing. In addition to that, though, homebrewers determine the character of their beer in their choice of yeasts.
Ale yeasts will typically begin fermentation very quickly because they can withstand higher temperatures. The entire fermentation process for an ale is typically pretty quick, usually just a couple of weeks or so. On the other hand, lagers require a slower, cooler process, so it’s best to avoid a lager for a speedy fermentation.
Other faster brews include:
- Kveik, a Norwegian strain that can reportedly finish primary fermentation as quickly as 48 hours, which could cut total time from brew day to glass pour in half compared to other strains.
- Belgian-style strains, such as Wyeast 3724 or White Labs P611. Such strains can tolerate higher temperatures and higher alcohol levels.
- Session or low ABV beer, as the yeast won’t have to work very hard to reach final gravity.
A yeast starter accelerates fermentation
A yeast starter is essentially a miniature batch of your beer that you will use to boost the production of yeast in your batch. Think of the starter as a nursery: a day before you decide to brew, you can make a smaller version of your batch to allow the yeast cells to multiply. Boil malt extract in water and allow it to cool, then add your yeast. There are calculators available online to help you.
This is a time you’ll want oxygen, so leave your starter in an open-top container (you can cover it with something thin like cheesecloth if you’d prefer). If you use an Erlenmeyer flask, you can boil, cool, and allow the yeast to activate all in the same container. Aeration helps the yeast get to work! If you have a stir plate, use it to incorporate air into your starter, but manually swirling the flask periodically works just fine too.
In that 24 hours before brew day, you’ll have built yourself a super-boosted colony of yeast that’s ready to speed up the fermentation of your batch! You know it’s ready if it’s foamy. It may also smell a little sulphuric, which is totally normal. Just give it a swirl to move that yeast around before pitching it in your cooled wort.
Be mindful of the temperature: if the wort is too cold, it’ll shock the yeast, and if it’s too hot, it’ll kill it completely. You want your starter and your wort to be within a few degrees of one another so the yeast has the perfect environment to thrive. That’s around 68°F.
Here is a great video detailing the entire process.
Not enough yeast will slow down beer fermentation
If you were hoping for a rapid fermentation, make certain you’ve measured your yeast out correctly. If there isn’t enough yeast, then they are spread too thin to efficiently consume the sugars of the wort. While yeast can tolerate a lot, we don’t want to add additional strain if it isn’t necessary.
If fermentation isn’t happening, you can repitch your yeast or use a yeast starter as described above. We’ve discussed before how your batch isn’t a lost cause just because it isn’t fermenting yet. It likely needs more yeast and a little patience from the homebrewer.
Higher wort temperatures will accelerate beer fermentation
While homebrewers end up spending a lot of time talking about yeast, we can’t forget about the other critical component of beer: the wort. It’s what feeds our yeast, and it needs to provide the perfect medium for that yeast to live and propagate. The package containing your yeast strain will display a temperature range. Pitch the yeast at the height of that range to accelerate fermentation.
However, you’ll want to use caution with this method. A higher, more aggressive temperature strategy runs the risk of producing off-flavors in the beer and potentially causing your yeast to underperform or die off completely, which could require repitching your yeast.
High ambient temperature will make fermentation faster
The environmental temperature has an impact on fermentation, as well. With an ale, for instance, the yeast is happiest when the environment is kept between 68-75°F. For a lager, that range is 48-58°F.
Yeast also likes consistency, which is why homebrewers want to avoid fluctuating temperatures during the fermentation process.
Just like how increasing the temperature of the wort will prompt the yeast to begin fermentation faster, a higher ambient temperature will do the same. The metabolic rate of the yeast will speed up with a bump of the thermostat but again, you may risk off-flavors or killing your yeast.
Aeration of the wort accelerates fermentation
Gently aerating your wort to introduce oxygen can prompt a faster fermentation. Yeast needs oxygen in order to extract nutrients from the wort and multiply. Stirring the wort to introduce air encourages the yeast’s metabolic rate and speeds fermentation. Without sufficient oxygen, fermentation may be delayed.
Increasing the ratio of yeast to sugar accelerates fermentation
You can speed up fermentation by increasing the amount of yeast in the wort. A higher concentration of yeast means faster sugar consumption, which in turn leads to more rapid energy conversion.
This method also presents its own pitfall, as the yeast are essentially competing for a limited resource and may not be able to reach peak health, which may result in underdeveloped fermentation flavors. Good news, though: it’s unlikely in homebrewing to pitch too much yeast.
How do you know if fermentation has started?
While it may seem as though nothing is happening for the first couple of hours after you’ve pitched your yeast, rest assured there’s a lot going on in this lag phase. You’ll know fermentation has started when you begin to see bubbles. These bubbles will increase and create foam, which will soon become your krausen or the foam cake on the surface of your beer. Check out this video that provides a great example of what krausen looks like. Your airlock will likely be bubbling away as carbon dioxide is released. Particles may be swirling in the beer as well, which indicates the presence of carbon dioxide.
If there’s no foam and your airlock seems sluggish, there’s no need to worry just yet. Measure the gravity with a hydrometer to see if there’s a change from your original gravity reading before you pitched the yeast. Byproducts of fermentation are carbonation and alcohol. Though the carbonation may not be as apparent as an active airlock or krausen, you’ll be able to tell that fermentation has started when calculating gravity.
We’ve created a helpful guide on how to spot fermentation so you can RDWHAHB (Relax, Don’t Worry, Have a Homebrew).