Ask Mr. Wizard

Quick Fermentations


Dustin Patterson • Alabama asks,

Whenever I use a yeast starter I have overly active fermentation for about four days and then almost no fermentation at all. Is this normal?


To answer this question I will assume that you do not have a chilly
root cellar where you are fermenting lagers, and that most, if not all,
of your homebrews are ales. I will also assume that you are fermenting
your brews in your house at about 72 °F (22 °C).

So, given this information, you want to know if a four-day fermentation
period for ales (assumed) is normal and the answer is unequivocally,
“Yes!” I think too many descriptions of homebrew fermentations are based
on using outdated methods where little packets of yeast were tucked
beneath the lids of extract cans and often not used quickly enough.

The quality of yeast, both dried and liquid, is much better these days
for a number of reasons — and I think the biggest reason is the strength
of the homebrew market and the demand for such products.

Yeast starters increase yeast population and allow the brewer to pitch
the yeast at high kräusen, or at least very shortly thereafter. This is
the period in the growth phase when cells are actively growing and is
named for the yeast froth (kräusen generally translates to ruffle or
curly) on top of the fermenting beer. The result of pitching yeast at
this stage of growth is what seems to many as abnormally vigorous
fermentation that seems to terminate too quickly.

Historically this type of vigor during primary fermentation was
extremely important since wort spoilage occurs quickly unless brewing
yeast become the dominate microbiological population. When yeast begin
to ferment the sugars found in wort, pH quickly drops, alcohol and
carbon dioxide concentrations begin to increase and the environment
becomes hostile to many aerobic wort spoilers. Sluggish fermentations,
on the other hand, leave the wort vulnerable for a longer period and the
chance of spoiled beer increases. The problems faced by brewers of the
past still exist today, albeit to a lesser degree because of
improvements in equipment design and our modern understanding of
microbiology, and the benefits of vigorous pitching yeast are equally
important today.

Aside from the argument presented above, rapid “normal” beer
fermentations generally produce cleaner beer. Many of the off-flavors
associated with fermentation, such as ex-tremes with higher alcohols,
esters, sulfur compounds, acetaldehyde and diacetyl, are associated with
weak fermentations.

On a practical note, we use White Labs WLP001 American Ale for most of
our ales at Springfield Brewing Company. Our primary fermentation period
for ales with original gravities between 11–14 °Plato usually is
complete in three days. There is nothing abnormal with seemingly-short
four-day fermentations!

Response by Ashton Lewis.