Hello,
We charted the fermentation of the last two batches of beer that we made and noticed some very interesting things. The most interesting thing is the difference in the shape of the graphs of bubbles per minute charted against time in hours of fermentation. I had assumed that the two batches would follow a similar fermentation progression. As it was, the Amber peaked much earlier and slowly tapered, while the Bitter Ale gradually increased in bubbles per minute, then rapidly dropped. The temp of the room was kept at a constant 66-68 degrees.



Is there differences in the yeast or other factors that would account for this? Do different varieties of yeast have distinct graphs of their fermentation? (We used Danstar Nottingham Yeast in the Amber and Doric Active Dry Brewing Yeast in the Bitter). One difference between the two batches was that the OG on the Amber was 1.050 whereas the OG on the Bitter was 1.042. Also, in the Amber, we started with a little bit less water and more boiled off so that there is about 1 gallon less in the Amber than in the bitter. Also, the expiration date on the yeast of the Amber beer was March 2006 and the expiration date on the yeast of the Bitter was June 2006.

The short answer is "yes," different yeasts will display different fermentation activity. Seeing it in a graph is cool stuff!

There is enough variation in the beers that the results are inconclusive. Gravity, dextrines, volume, aeration, hopping all play into how the yeast will act. It is interesting to see that these beers were not at full fermentation until 2 to 3 days after pitching.

Several things are not clear from your experiment. An Amber implies more crystal malt, and hence more dextrines, than a bitter. Did you use the same base malt? Are these all grain, or extract? Are they the same extract (base and manufacturer)? How much aeration did you use?

Some great yeast experiments have been done by taking a 10 gallon batch and splitting it to ferment with different yeasts. One even enlisted a brewpub to try 20 five gallon batches of Belgian Yeasts.

Keep taking the data though. Over time it'll reveal trends that you may use inselecting yeasts for brewing.

Kev.

Very interesting stuff,
You're right Kevin, there's too many variables that are not the same to be able to isolate the role and behavior of the yeast itself. Do you know where the results of those experiments could be found?

We used Muntons Amber Malt Extract and ID Carlson Amber Spray Dried Malt in the Amber and 6.5 pounds of liquid malt in the bitter. As far as aeration, nothing too high tech here, we simply shook up the carboys before we fitted the airlocks.

I think it would be fun to do some experiments like the ones that you mentioned, keeping more variables the same.