Primary Fermentation

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The Beer Brewing Process
1. Preparing the Ingredients
2. Cleaning and Sanitation
3. Making the Wort
4. Boiling the Wort
5. Cooling, Racking, and Aerating
6. Pitching the Yeast
7. Primary Fermentation
8. Conditioning the Beer
9. Packaging and Carbonation
10. Dispensing and Serving

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.

Primary Fermentation for the Beginning Homebrewer

As a beginner, you'll probably be using the plastic bucket fermenter that came in your equipment kit. Assuming you have a bucket fermenter and a fermentation lock, the most important thing you can do is find a location with a stable, appropriate temperature for your yeast to work.

The Fermentation Environment

Once the wort is aerated and the yeast has been 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 72 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.

A Carboy fermenting beer with a Three Piece Airlock on top.

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

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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. Being plastic and lightweight, they are the easiest to work with and can be stacked on top of each other when not in use (for storage) and being cheap they are easily replaced if they become damaged. They also have a tap which facilitates easy racking (transfer of liquid) to bottles, secondary fermenter or a keg.

Glass Carboy

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Some home brewers use 6.5 gallon glass carboys as their primary fermentation vessel. While more expensive then plastic buckets, glass is easier to clean and sanitise and cannot be scratched when scrubbing. However the small opening of the glass carboy makes them difficult to clean (for example with a brush) when compared to a plastic fermenter. The use of a funnel is also required when filling the carboy and adding ingredients. There is also no tap included in a glass carboy so racking must be done with a siphon.

Stainless Steel Conical

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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.

Plastic "Better" Bottles

Various grades of food safe plastic are used to manufacture what are essentially "plastic carboys" or "water cooler" bottles. Many brewers swear by these bottles, while others argue that they may be semi-permeable, and eventually allow oxygen into the fermenter. Either way the fact that they do not break when dropped makes them in at least one way superior to glass fermenters. Some of these bottles hold exactly 5 gallons, and so are not suitable for fermenting a 5-gallon batch which would produce another half gallon or so of krausen. They are good for smaller primary fermenters and for conditioning or "clearing" tanks, although conventional wisdom says not to bulk condition in them for more than a month or so.

Airlocks and Blow-Offs

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The majority of modern brewing is done in a closed environment through the use of airlocks which allow carbon dioxide produced during fermentation to escape while preventing unwanted microbes from getting into the beer.

A "Blow Off" is a modification of an air lock. It is typically a hose attatched to the primary fermentation vessel where the air lock usually goes. The other end of this hose is run into a container of water or sanitizer and submerged. The resulting C02 can "bubble" out of the hose and the container like a normal air lock. The purpose of the blow off hose is to allow krausen to spill out through the hose and into the container if it grows too large for the space allowed by the fermentation vessel.

Fermentation Temperature Control

Given the importance of temperature during primary fermentation, many brewers have devised methods of controlling the temperature ranging anywhere from placing the fermenter in a water bath to utilizing chest freezers and a digital temperature controller.

Inexpensive temperature control methods include:

  • Placing the fermenter in a water bath. This increases the thermal mass of the fermentation system, and can stabilize temperatures in changing ambient temperatures. If heating is required, an aquarium heater is employed by some homebrewers to a) increase the temperature of the system and b) ensure a stable temperature. A heater with a temperature control is recommended, but be wary that most do not go below 67F / 19C.
  • Wrapping a wet towel or T-shirt around the fermenter. This works best if the bottom of the towel/T-shirt is left in the water and a fan is aimed at the fermenter. Brew Strong suggests that this works better in dry climates.<ref></ref>
  • Modifying a large cooler (60 quarts or more) to fit the fermenter along with several bottles of ice.
  • Moving the fermenter to a cooler location. Specifically one that may be thermally independent and/or stable (e.g. a closet).

Advanced temperature control typically involves the purchase of a refrigerator or chest freezer and a digital temperature controller. Many home brew supply shops carry these controllers for home use.

Another popular temperature control method for home brewers who do not have the space or budget for a refrigerator or freezer is the Son of Fermentation Chiller, a fun and easy Do-It-Yourself project for those who want to build their own fermentation chamber. While more involved than simply purchasing a cooler, this fermentation chamber tends to hold temperatures more easily and constantly than the modified cooler method discussed above.

When is Primary Fermentation Complete?

Primary fermentation typically takes anywhere from 7-14 days and is considered finished when the fermentation process is complete. So-called "secondary" fermentation is for conditioning and clearing the beer rather than additional fermentation.

Beer should be left in the primary fermentation vessel for at least 7 days, even if fermentation appears to be complete.

The only way to determine whether or not fermentation has finished is by taking gravity readings on consecutive days; if this reading remains constant, fermentation is complete. Some home brewers use the lack of airlock activity or the fallen krausen as an indication that fermentation is finished but these methods are inaccurate and can be misleading. If you think your fermentation is done, use your hydrometer to make sure.

What do I do next?

Once primary fermentation is complete, you may want to condition the beer through a secondary fermentation stage or lager it if appropriate. If not you can skip straight to the final step in the beer brewing process: Packaging and Carbonation.