Beginner’s Guide to Home Brewing – Fermentation

Now it is time to put the carboy in a controlled environment where temperature is constant and light excluded. As I said for an ale the temp. should be kept at 60-72 F and lagers at 50-60 F. All beer should be protected from light and if you ever had “skunky” beer you’ll know why. I cover the fermenter with paper bags and keep it in a closet away from variable temp changes and light sources. Keep a record of all you did today and of the temp in you fermentation area regularly throughout the next few weeks this way you can compare your results to future batches.

Brewers refer to fermentation in terms of primary and secondary. In the 6 ½ Gal. carboy the initial “roiling” fermentation is called primary. After about 7 days the activity dies down, the foam recedes and racking to a clean 5 Gal. carboy removes the beer from the sediment. If possible purge the clean and sanitized carboy with CO 2 to remove the possibility of aerating the beer.

You can tell primary fermentation has started by the bubbling and foam production that can be very vigorous depending on the yeast being used. At times the foaming can be too much for the vessel you are using so you will have to hook up a blow off tube. Sterilize a one-hole stopper and insert a short length of plastic tubing like that of the racking cane. Attach some flexible tubing to it, remove the airlock that is foam clogged and pop the new setup on the carboy. Put the end in a jug that has a few inches of SSS to prevent contamination. As things die down remove the blow off setup and recap with a clean airlock with vodka. Secondary fermentation is now beginning.

Fermentation times vary with the style of brew you are making, ales usually are complete in 2-3 weeks and lagers a few extra weeks past that. A good way to tell if the brew is finished is by measuring the specific gravity. Transfer a sample with a clean and sterile pipette from the fermenter to your hydrometer. Most yeast will attenuate (completed fermentation) at around 75% so if you started with a S.G. of 42 your final S.G. will be around 11. A higher gravity results in a sweeter more robust brew that is usually indicated in a particular style. Note that S.G. is measured as 1.000 being water and beer usually from 1.035 to 1.070 and for simplicity sake when referring to S.G. we drop the 1.0 and leave the last two digits. 1.045 g/cc as S.G. 45

More about fermentation

I have found that fermentation is usually complete when the air lock pops once per minute or longer. From this point on many complex processes are occurring. Diacetyls (buttery flavors) are being reduced by the yeast. Remember temperature control is always critical and should remain as constant as possible except in recipes where temperature reduction is needed to lager or age the brew. If kept in the low 60 range this ale will continue to age and clear.

One concern is yeast autolysis where yeast die off in large numbers consuming themselves and creating a sulfur odor. This is the result of storing beer at high temperatures for extended periods of time. The beer is considered spoiled and of no value.

When all goes well with fermentation, time and temps are maintained the yeast go into a dormant state and very few remain active. These last few struggle to feed on whatever fermentable sugars are left and reduce the S.G. slightly as their comrades fall out of solution and settle to the bottom of the fermentation vessel. Other activities in the vessel include the settling out of unwanted proteins, tannins and polypeptides etc. Through experience you will get to recognize the various aspects that are beneficial and those that are harmful.

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