Thursday, May 7, 2009

The gravity of the situation

It's now five days into primary fermentation for batch 090501 and the krausen has settled. There's still bubbling in the airlock but it's slowing down, and I thought it would be a good time to take a sample and check the specific gravity. The beer mavens at HBT are adamant that watching the bubbles is not enough; the only way to tell whether fermentation has stopped is to measure the specific gravity and see if it continues to decline. (The more sugar is converted to alcohol by the yeast, the lower the gravity goes. Ergo, if the gravity flatlines, no more conversion is taking place and the yeasties have called it a day.)

The OG (the original specific gravity prior to fermentation) was measured as 1.042, which was right at where it was supposed to be based on the recipe expectations. Tonight, I measured the gravity again, and it came out as 1.0166 (actually I measured 1.016 but at 66 F, which when adjusted for temperature vs. the standard of 60 F, yields 1.0166). The target FG (final specific gravity) for northern English brown ales is in the range of 1.008-1.013, and BeerSmith is predicting that this batch will end up at 1.013, so we still have some distance to go.

The best part about this testing process is that you're not supposed to reintroduce the sample to the batch because of the contamination risk, so you have to drink it. (I guess you could pour it out, but that seems a waste.) The taste was quite good, very like a Newcastle to my taste buds, so it seems that this experiment may actually turn out well in spite of the brewer's lack of skills.

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