From the HBD Archive
From: "1107-CD&I/VIRUS DISEASES" <henchal@wrair-emh1.army.mil>
Subject: specific gravity problems, over-carbonation
Date: 1989-06-20 18:40:00 GMT

John Mellby writes
"I am having {problems} with my ale. In the last leveral
batches I have a high terminal gravity between 1015 and 1020."

You don't mention what your starting gravity was, but you can
expect the attenuation of your ale (the differnece between the
starting gravity and the final gravity) to be between 65-80%.
The factors which affect the final specific gravity are as
follows:

1. The strain of yeast. Wyeast and other suppliers are now
providing the attenuation characteristics of their yeasts. This
data is helpful for when you craft beer. You can select yeasts
to be light (with high attenuation) or strong (with low
attenuation) body depending upon your desires.

2. The extract. The way that the grain was mashed
significantly affects the final gravity. Some extracts are made
at higher mash temperatures which result in a greater proportions
of limit dextrins in the malt extract. If you are a grain
mash/brewer this is one of the characteristics you can control.
The length of time you mash the grain at the saccharifying
temperature also controls the amount of dextrins in the extract.
Wworts with a higher percentage of dextrins have lower
attenuation and high final gravities.

3. Contamination. Contamination of the primary
fermentation can result in a "stuck" fermentation. In this case,
yeast and contaminating microorganisms compete for essential
nutrients. The fermentation cycle is interrupted by the
decreasing efficiency of the yeast to perform the intended job.

John also writes,

"...and despite using as little as 1/2 c of sugar for priming 5
gallons, the bottles are over-carbonated."

The most common cause of over carbonation, if the correct amount
of priming sugar is being used, is bacterial contamination. For
a detailed discussion see the Troubleshooting Issue of Zymurgy.

I hope that this is helpful.

ERIK A. HENCHAL
<Henchal@WRAIR.ARPA>



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