Is Yeast Autolysis Really a Problem with Home Brewing Beer?
Yeast autolysis. The dreaded condition whereby the diseased and mutated yeast violently explodes and spews foul flavors into our beers before permeating the room, the house and eventually our souls! Okay, that’s hyperbole, but hey, isn’t it fun? In terms based on reality (a place where I prefer not to be), yeast autolysis is the process where yeast cells die, burst their cell walls (autolize) and release unwanted compounds into the beer. I like the dramatic explosion analogy better. High degrees of yeast autolysis lead to off flavors such as sulfur, rubber, soap, or even meaty notes, and unless you’re tossing meat into your fermenter, we’re guessing you probably don’t want the meaty notes in there.
Yeast autolysis has long been a concern among home brewers – the concern about leaving beer in the primary fermenter for too long, the yeast dies, and… you know the rest of the story. However, our understanding of yeast autolysis in the context of homebrewing has evolved significantly.
The History of Exploding Yeast (Or, Autolysis in a Nutshell)
Professional breweries think they’re so mighty. They look down upon us with their towering, conical fermenters, where we cower below, fearfully peering up beside our 7-gallon buckets. But professional breweries have an Achilles heel. Their fermenters are gargantuan, and their yeast sediment depth is measured in feet. And the pressure at the bottom of their haughty, towering fermenters is tremendously high, and this pressure can cause yeast death and autolysis if the beer is left on the yeast cake for too long.
In the early days of homebrewing, and long before the internet, home brewers relied on books to learn about the craft. Few books existed on the topic, and many were based upon a combination of lore with an integration of practices adopted from the professional brewing industry. Professional breweries, because of their tall fermenters, absolutely had to be wary of autolysis, so these early beer writers assumed home brewers had the same concern. We read these books and took the information as gospel. Thus, home brewers manically racked their beer from the primary fermenter to a secondary fermenter—often within a week—to avoid this dreaded autolysis. Now that the beer was safe from autolysis, as home brewers believed, they could safely allow the beer to settle and clarify in the secondary for a longer time.
Our Modern Understanding of Autolysis and Homebrewing
Home brewing has come a long way since its early beginnings when we sprinkled mostly dead yeast over our oxidized wort made from bulging cans of malt extract. Today, home brewers actively research new brewing techniques, which has expanded our collective homebrewing knowledge exponentially. And while today it may sound obvious, we have learned that our homebrew environment does not resemble commercial breweries:
- Fermenter Size and Pressure: Compared to professional breweries, homebrewers fermenters (5 to 10 gallons) are laughably smaller. The pressure on the yeast cake at the bottom of our fermenters is fractionally less than at professional breweries. Thus, we have a low risk of yeast autolysis.
- Improved Yeast Health: Compared to the abysmal yeast quality of yesteryear, the quality and viability of modern yeast strains have improved by orders of magnitude. Our modern yeast is robust and less prone to autolysis. This is true for both liquid and dry yeasts.
- Extended Primary Fermentation: Many experienced homebrewers now, if desired, leave their beer in the primary fermenter for three to four weeks, sometimes even longer, without experiencing any autolysis-driven off flavors. Conversely, this extended aging time allows the yeast to clean up byproducts of fermentation, such as diacetyl (movie theater popcorn butter) and acetaldehyde (green apple), leading to a cleaner, more polished final beer.
- Reduced Need for Secondary Fermenters: Today for most styles of beer, homebrewers do not use a secondary fermenter. Of course, exceptions apply. When brewing IPAs, homebrewers find using a secondary helpful to manage the various stages of dry hoping. Also, homebrewers will commonly use secondary fermenters for aging beer on fruit, wood, or other adjuncts.
- Increased Need to Make Life Easy: So maybe this plays to the laziness in all of us, but if you don’t need to use a secondary for a specific purpose, then why bother? We all appreciate saving time, and having more time means we have more time to drink beer, and if a secondary’s use is unnecessary, then skip it. After all, each time you transfer the beer between vessels, you increase the risk of oxidation and the omnipresent risk of bacterial contamination.
Final Thoughts on Maniacal, Suicidal Exploding Yeast (Okay, Autolysis)
Among the modern homebrewing elite (and if you want to be elite, then think like us!), our consensus is that leaving beer in the primary fermenter for extended periods—up to a month or more—is safe and can even be beneficial. Homebrewers’ fear of autolysis was overblown, because we assumed professional breweries’ methodology also applied to us, which it didn’t. And with this paradigm shift, we can spend less time worrying about non-issues and unnecessarily transferring the beer and spend more time drinking the beer, which is where our priority should be!
