Continuous fermentation (part two)

I’d always laboured under the assumption that the main reason for dropping continuous fermentation was that it produced beer that tasted shit. I’m now beginning to doubt this. At least as the main cause of the system being ditched.

According to taste tests carried out by Bishop, continuously fermented beer only scored marginally worse than that produced by batch fermentation. Though with just six tests, the sample size was pretty small.  As further proof, Bishop comments that continuous fermentation beer wasn’t blended with batch fermented, as would have been the case if there were significant flavour differences. And none of the customers complained.  (The least ringing endorsement that you can imagine – no-one complained.)

According to George Thompson, who ran the system at Drybrough, even the quality control people in London couldn’t tell the difference between batch and continuously fermented Heavy. 

Yet, in the late 1970s and early 1980s, UK brewers abandoned the system. If the beer quality was acceptable, why was this the case? You can probably guess: economics.

Continuous fermentation systems were good at producing large volumes of a single beer, but rather inflexible. Switching from one beer to another could be a complicated and lengthy process. Running the systems proved more difficult than expected, requiring constant monitoring by highly skilled personnel. Making them more expensive to run than batch systems. 

In addition, there were big advances in cylindroconical technology, speeding up batch fermentation and providing a more flexible method of fermentation. 

At Drybrough, it was probably the need to monitor the system 24/7 and the cost of employing shifts of workers for the task, which the conical fermenters didn’t require. 

I was most intrigued by the impact of the system on yeast. In the early days, Drybrough’s system was run for very long periods – more than six months. But it was found that the yeast began to change at certain point, leading to a different flavour profile in the beer. To prevent this, the system was brought down twice a year: midsummer and midwinter. 

Yeast harvested from the continuous fermenter was more vigorous than that from conicals and at Drybrough was used to ferment stronger beers. 

This is an excerpt from my book on 1970s brewing, "Keg!". Get your copy of "Keg!" now!

Listen to George Thompson, who ran the last continuous fermentation system in the northern hemisphere, talk about the process.