Yeast bite is one of those homebrewing terms that you hear from time to time accompanied by the stern warning to avoid it in your beer. But ask someone to describe yeast bite and you may hear the answer, “Well, it’s yeasty, like the bite of a slurry of yeast.”

We’ve all had excellent brews that had a noticeable “yeasty” character. Perhaps in subtle aromas and flavors of freshly baked bread. Or in the unique, mouth-filling, chewy experience of a good, cloudy hefe-weizen. Or in the yeast-induced complexities of a Belgian ale. So what exactly is yeast bite? What does it smell like, taste like, and how does it get into your beer?

Yeast bite is a term that describes a number of different undesirable flavor and aroma characteristics that are directly related to the type of yeast used and the manner in which it is used. The flavors and aromas associated with yeast bite have been described variously as smelling like rancid fats (cheesy, soapy, pukey) or beef or chicken soup or bullion, tasting of fatty acids, rotten, having a rubbery or sulfury stench, and imparting a sour, bitter taste to beer.

The American Homebrewers Association’s beer scoring sheet, used at homebrew competitions around the country, makes its mention of the characteristic under the simple heading “Yeasty,” which it describes as, “yeast-like flavor. Often due to strains of yeast in suspension or beer sitting on sediment too long.”

Though there is a range of definitions of yeast bite, perhaps the AHA’s simple description is the closest. It seems that yeast bite is a phenomenon that falls into two categories: that which is caused by live yeast in suspension in your beer and that which is caused by dead yeast in sediment.
    
Live Yeast in Suspension
In contrast to the aroma and flavor of freshly baked bread, imagine, or better yet taste, the flavor of freshly prepared yeast slurry, dried yeast, or yeast tablets, or pick up a container of the B complex vitamins, an approximation of yeast flavors. None of these are altogether pleasant. Excessive amounts of live yeast that remain in suspension in your beer during both fermentation and bottle conditioning might cause this flavor to come through. Different strains of yeast will have and produce different flavors and will behave or misbehave depending on their fermentation temperatures.

During fermentation all yeasts will flocculate, or clump together, and settle to the bottom of the fermenter. Different yeast strains, however, have different tendencies to flocculate. Some yeasts may clear completely from the beer after primary fermentation while others will stay suspended for much longer.

Some hefe-weizen brewers, for example, choose a strain that has poor flocculation tendencies, thereby resulting in a beer that remains cloudy through the fermentation process and into the mug. These strains are carefully chosen and have flavor characteristics that complement the grains and hops used to produce a beer with a crisp, fresh, and slightly yeasty flavor.

In other types of beers, however, poorly flocculent yeast may taste harsh or bitter and detract from the beer’s quality. If, after primary fermentation is complete, your beer remains cloudy and the yeast doesn’t appear to be dropping, you may have a poorly
flocculating yeast strain.

You can remedy this problem in two ways. The first is as simple as changing yeast strains: Ask your supplier for a more flocculent strain. The second is by inducing the yeast to drop out of suspension more rapidly before bottling. The easiest way to do this is to lower the temperature of the fermentation vessel. The colder the temperature, the faster yeast will drop from solution. An alternative is to rack the beer off the sedimented yeast and let it stand for several more days in a second fermentation vessel.

Another cause of yeast bite in your homebrew might be overpitching, or adding too much yeast to the fermenter at the start of fermentation. This will not generally be a problem for homebrewers, unless they are getting yeast from a local brewery and pitching an amount of pure slurry that is far too great. Overpitching yeast will result in much more yeast in solution that could break down to give yeast-bite flavor. Two dried yeast packets or yeast from a smack pack is adequate for a five-gallon batch, but culturing the yeast up into a one-pint starter will supply a better number of healthy cells. In any case a normal pitching rate (2.5 to three ounces of pure, healthy slurry for a standard
five-gallon batch) won’t give rise to yeast bite if proper handling after fermentation follows.

Length of fermentation and fermentation temperature are also important yeast-bite considerations. A fast, warm fermentation racked immediately into bottles will leave lots of yeast in suspension in the bottles and will also result in a thicker layer of sediment as the beer matures. Keep your fermentation temperatures well within the range for the style you are brewing, allow the yeast to settle for several days after primary fermentation, and rack the beer into another container, if possible.
    
Dead Yeast: Autolysis
At the end of fermentation, when most of the yeast has settled into a hard pack of sediment, some of the cells will begin to die and undergo a process called autolysis. Autolysis is probably the single most important contributor to yeast bite. “Lysis,” the dissolution or disintegration of the cell, coupled with “auto,” self, basically means “self-destruction.” Simply put, when yeast cells die at the end of fermentation, the yeast’s own enzymes begin to digest the yeast cell itself. This process releases all kinds of nasty compounds into the beer, including fatty acids and sulfur- and nitrogen-containing compounds that cause the aromas and flavors described above as meaty, rubbery, and sour.

Autolysis does not occur immediately after sedimentation but rather is a gradual process. Temperature plays a large role in the rate of yeast cell decomposition. The type of yeast and the yeast’s overall health will also contribute to the rate of autolysis. If you have been experiencing possible yeast bite in your beers, here are some things to try:

Rack your beer. After primary fermentation is complete, let the yeast settle, but don’t leave it sitting on the yeast sediment for too long (more than about a week after primary is complete is too long).   

Control the temperature during all stages. Heat will rapidly accelerate the autolysis process. Keep the fermentation and conditioning
temperatures down and store the bottled beer in a cool place.

Remove as much yeast prior to bottling as possible. More yeast means more autolysis and nasty flavors.
    
Autolysis in Bottle-Conditioned Beer
While removing beer from a sediment of possibly decomposing yeast is very important before bottling, it is less important in the bottle. Although the same breakdown occurs, physical conditions in bottle-conditioned beer are very different from conditions in the fermenter. Most likely, all yeasts will autolyze given enough time.

In the fermenter there is a large volume of yeast contained in the sediment pack, and most homebrewers ferment their beer at warm, ambient temperatures. Once the beer is racked off the yeast and bottled, however, there will be a substantially smaller volume of yeast in the bottle that could be subject to autolysis. Furthermore, most homebrewers store some, if not most of their beer in the refrigerator. Cold temperatures will inhibit yeast decomposition and prolong the life of the beer.

It seems that stronger beers, such as barleywines and other beers that contain yeast in the bottle and are capable of prolonged storage, suffer less from the effects of autolysis. This is probably due to a number of factors that include the presence of esters and higher alcohols that might tend to mask any characteristics of autolysis.