Use of Secondary Fermenters (Optional)
Using a two stage fermentation requires a good understanding of the fermentation process. At any time, racking the beer can adversely affect it because of potential oxygen exposure and contamination risk. Racking the beer before the Primary fermentation phase has completed can result in a stuck or incomplete fermentation and too high a final gravity. Simple extract ales do not need to be racked to a secondary fermenter. It can improve clarity and aspects of the flavor, but wait until the second or third beer when you have more experience with the brewing processes.
The reason for racking to a Secondary Fermenter is to prevent a yeast breakdown called autolysis, and the resulting bad taste imparted to the beer. This will not be a problem for these relatively short fermentation-time ale beers. Other beer types, like Lagers and some high-gravity beer styles, need to be racked to a secondary because these sit on the yeast for a longer period of time.
The following is a general schedule for a simple ale beer using a secondary fermenter. Allow the Primary Fermentation stage to wind down. This will be 3-4 days after pitching when the bubbling rate drops off dramatically to about 1-5 per minute. Using a sanitized siphon (no sucking!), rack the beer off the trub into a another clean fermenter and affix an airlock. The beer should still be fairly cloudy with suspended yeast. Racking from the primary may be done at any time after primary fermentation has more-or-less completed.(Although if it has been more than two weeks, you may as well bottle.) Most brewers will notice a brief increase in activity after racking, but then all activity may cease. This is very normal. Fermentation (Conditioning) is still taking place, so just leave it alone. A minimum useful time in the secondary fermenter is two weeks. Overly long times in the secondary (for ales- more than 6 weeks) may require the addition of fresh yeast at bottling time for good carbonation. This is usually not a concern.
For more information, see the Recommended Reading section.
A Word About Hydrometers, a hydrometer measures the relative specific gravity between pure water and water with sugar dissolved in it. The hydrometer is used to gauge fermentation by measuring one aspect of it, attenuation. Attenuation is the conversion of sugar to ethanol by the yeast. Water has a specific gravity of 1.000. Beers typically have a final gravity between 1.015 and 1.005. Champagnes and meads can have gravities less than 1.000, because of the large percentage of ethyl alcohol, which is less than 1. By the way, hydrometer readings are standardized to 59F, since liquid gravity (density) is dependent on temperature. Temperature correction tables are usually sold with a hydrometer or are available from Chemistry Handbooks (ex. CRCs). Here is a short table of corrections:
50F => -.0006
55F => -.0003
59F => 0
65F => +.0006
70F => +.0012
75F => +.0018
80F => +.0026
85F => +.0033
A hydrometer is a useful tool in the hands of an experienced brewer who knows what he wants to measure. Various books or recipes may give Original and/or Final Gravities (OG and FG) of a beer to assist the brewer in the evaluation of his success. For an average beer yeast, a rule of thumb is that the FG should be about one-fourth of the OG. For example, a common beer OG of 1.040 should finish about 1.010 (or lower). A couple points either way is typical scatter.
It needs to be emphasized that the stated FG of a recipe is not the goal. The goal is to make a good tasting beer. The hydrometer should be regarded as only one tool available to the brewer as a means to gauge the fermentation progress. The brewer should only be concerned about a high hydrometer reading when primary fermentation has apparently ended and the reading is about one half of the OG, instead of the nominal one-fourth. Incidentally, if this situation occurs, two remedies are possible. The first is to agitate or swirl the fermenter to rouse the yeastbed from the bottom. The fermenter should remain closed with no aeration. The goal is to re-suspend the yeast so they can get back to work. The alternative is to pitch some fresh yeast.
Hydrometers are necessary when making beer from scratch (all-grain brewing) or when designing recipes. But the first-time brewer using known quantities of extracts simply does not need one.