Primary fermentation is when the wort finally becomes beer through the conversion of sugars into alcohol and carbon dioxide. This conversion is done by the yeast which "eat" the sugars; you just need to provide the right conditions for the yeast to do its job.
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The Fermentation Environment
Once the wort is aerated and the yeast has been added pitched, the yeast should begin to reproduce, and eventually ferment the beer converting the fermentable sugars into alcohol and CO2.
Signs of fermentation include bubbles (burps) in the airlock and a layer of foam called krausen on top of the beer. The amount of time between pitching the yeast and the first signs of fermentation is referred to as "lag time". The goal of the attentive brewer is to keep the lag time within a reasonable limit. Lag times typically vary from as short as a few hours to as long as 48 hours. Using a yeast starter and aeration methods, as well as keeping the fermentation temperatures within the accepted range, can help to reduce lag time.
Most ale fermentations should be mostly complete within 10 days although fermentation times can vary anywhere from 4 days to 3 weeks. Lagers may take longer to finish fermenting, typically 2 to 3 weeks, and require at least a month of lagering.
A critical component to the fermentation environment is the temperature of the wort at pitching and during fermentation.
Fermentation Temperature
The appropriate fermentation temperature varies from one yeast strain to the next. In general, ales ferment anywhere between 60 and 70 degrees F while lagers ferment between 50 and 60 degrees F. Fermenting at too low a temperature can result in a slow or "stuck" fermentation in which the yeast become dormant before all the sugars have been converted. Fermenting at too high a temperature can lead to off-flavors due to the production of esthers. There are different steps brewers can take to control the temperature throughout the fermentation process.
Choosing the Right Fermentation Vessel
There are three commonly used vessels for primary fermentation: plastic food grade buckets, glass carboys, and stainless steel conical fermenters. Which one you choose is largely a function of cost, ease of use, and technique.
Plastic Buckets
6.5 gallon plastic food grade buckets are the most common fermentation vessel for the new brewer; they are often sold with beginner equipment kits.
The principle advantages of using plastic buckets for fermentation are that they are easy to use and clean and are the least expensive option. Since the top is wide open, the wort can be poured in quickly without the use of a funnel or siphon; the wide opening also makes cleaning much simpler.
The main disadvantages are that they scratch easily making them difficult to sanitize, it is not possible to view what is occurring during fermentation without opening the lid thus exposing the beer to possible infection, and the plastic is oxygen permeable which limits the amount of time the beer should spend in the bucket. For these reasons many people switch to glass carboys after their first few brews.
Glass Carboy
The majority of home brewers use 6.5 gallon glass carboys as their primary fermentation vessel. While not as inexpensive as plastic buckets, carboys eliminate the disadvantages associated with buckets and are only moderately more difficult to work with.
The small opening at the top of the carboy necessitates the use of a funnel or siphon when adding the cooled wort to the fermenter. In addition, the small opening makes carboys more difficult to clean; typically a carboy brush and bottle washer are required.
Stainless Steel Conical
Conicals are significantly more expensive than either buckets or carboys running anywhere from $500 to several thousand depending on the size and accessories. Some home brewers use conicals because it allows them to remove the trub from the cone in the bottom without racking and disturbing the fermenting beer. This allows both primary and secondary fermentation to occur in the same vessel. Many conicals are also fitted with a spigot allowing the brewer to bottle or keg their beer more easily.
Airlocks and Blow-Offs
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Advanced Fermentation Temperature Control
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When is Primary Fermentation Complete?
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Primary fermentation is finished when fermentation is finished. Secorndary is not for fermenting, it is for conditioning and clearing. Also used to clear the vessel used for primary fermentation for another bre.
What do I do next?
Once primary fermentation is complete, you may want to take extra measures by way of Conditioning the Beer, such as a secondary fermentation or lagering. Or, beginning brewers can skip straight to the final step in the beer brewing process: Packaging and Carbonation.
