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?
Dustin Patterson
Alabama

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 I think too many descriptions of homebrew fermentations are based on using outdated methods where little packets of yeast were tucked beneath the lids of extract cans and often not used quickly enough.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!