Sunday, 10 June 2012

A Dropping Problem.

British brewershad some adjusting to do after WW I. It took them a while to get the hang of brewing low-gravity beers.

During the 1920's and 1930's brewers acquired new skills. They learned how to tweak recipes and techniques to compensate for the lower strength. Britain's brewers became masters of producing stable, flavoursome beers of modest gravity. It's something they still excell in today. Where else are beers of less than 4% ABV brewed that actually taste of something?

This is an example of brewers adapting to the new circumstances. It concerns the dropping system of fermentation, which used to be common, especially in th South. Fermentation started in tall round vessels and then transferred (dropped) into shallow square vessels. It helped aerate the wort and stop the remperature of the wort rising too much. It also aided clarity, as much sediment was left in the round.

"A Dropping Problem.
It is customary, in dropping equate breweries, to drop or cleanse the fermenting worts at or about the period of half-gravity. This procedure answered well enough when gravities were liberal, but since the compulsory advent of weak beers, some few workers have found that if allowing fermentation to proceed to the limit of half-gravity before dropping to shallow skimmers, the necessary increment in heat does not always take place during the colder months of the year, with the result that the fermentation receives a more or less severe check which is apt to leave its imprint on the finished beer. Limited depth of wort and aeration at dropping are naturally conducive to increased reproductive activity and a corresponding tendency for yeast to rise to the surface before full attenuation and purging of the fermenting fluid is accomplished. No great harm may come of this while the weather remains cold, but matters should certainly be adjusted before the advent of summer, since high racking finals coupled with insufficient purging of wort are certain forerunners of disaster under anything like forcing conditions of temperature, The matter is a simple one and essentially practical, and by restricting the temperature in the collecting vessel and arranging to drop the worts at an earlier period, normal and sufficiently extended attenuation usually results, assuming, of course, that materials and procedure are in order."
Brewers' Journal 1921, Page 115.
Seems to make sense. A weaker beer need to be dropped earlier.

As I have brewing records from breweries using the dopping system that span WW I, it was easy enough to check if they changed when they dropped.

I looked at Fullers first, as I've a good set of their records. Except they never let the wort get anywhere near half gravity. They usually dropped after around 12 hours, so nowhere near half gravity. Both before and after WW I. I could see no change.

Next I tried Kidd. Their records have a full fermentation record and indicate when dropping occurred. This is what I found.

This is a batch of X brewed 5th April 1917:

And this is one brewed on the 25th February 1936:

As they'd switched from brewer's pounds to specific gravity, I'll convert the first lot to SG: 15.4 is  1042.7º and 9.4 is 1026º. Mmm. The 1917 brew was dropped when the gravity was 61% of the OG. So well above half gravity. The 1936 brew was dropped when the gravity was 42% of the OG. Or well below half gravity.

The same story is repeated for all Kidd's beers. In the 1930's they were waiting longer before dropping than they did in 1917. The exact opposite of what the article says. Isn't that confusing?

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