Last week, I described the basic idea behind the forced fermentation test. Basically, you overpitch a small sample of wort, and ferment it at high temperature. The sample will reach it’s final gravity (FG) before your main batch of beer. Knowing the FG of the sample will tell you what the FG of the your beer will be. This can be good to know when you are deciding whether to bottle. Here’s how to perform the test. [Read more…]
Brewers, especially new brewers, may wonder what the final gravity (FG) of their beer should be. Perhaps their barleywine stopped fermenting at SG 1.022 and they are wondering if it’s done or the fermentation is stuck. This is something the FG alone can’t tell you.
Established recipes frequently list an expected FG, and these should be a good estimate if you follow the recipe exactly. If, however, you’re formulating your own recipe — or modifying an existing one — the FG depends on three main variables. First, every yeast strain has a different range of apparent attenuation. Secondly,grain bills can be mashed to yield more or less fermentable worts. (Likewise, different malt extracts yield worts of differing fermentabilities.) And finally, some kettle adjuncts are more or less fermentable than wort made from mashed grains or dissolved malt extract. Table sugar (sucrose), for example, is 100% fermentable. In contrast, milk sugar (lactose) is not fermentable by brewers yeast. Although it may be possible to calculate a likely FG, you can determine experimentally what your FG will likely be with the forced fermentation test. [Read more…]
This article is part of a series on barleywine, the second in a section on fermentation.
Yesterday, I discussed getting a barleywine fermentation started — aerating the wort and pitching the yeast. Today, after explaining one additional step you can take, I’ll discuss guiding the fermentation to it’s conclusion and conditioning the beer.
Forced Fermentation Test
A forced fermentation test is a way to predict the final gravity of your beer. To perform this test, take a small sample of wort, pitch an excess of yeast and ferment it warm. For a 5-gallon (19-L) batch of barleywine, take a sample just large enough to float your hydrometer (about 8.5 fl. oz./250 mL). Place the wort in a sanitized jar with a lid and aerate it thoroughly. Pitch about 2 tsp. of thick yeast slurry and hold the jar (with the lid loosened) at around 80 °F (27 °C), or as warm as you can manage. The sample should ferment quickly due to the high pitching rate and warm temperature. The final gravity (FG) it reaches will tell you what to expect your main batch to ferment down to. This can help you distinguish between a stuck fermentation, and one that is simply complete.