Continuous fermentation

A dream of some large brewers was continuous fermentation. Where fresh wort was continuously added to fermenters as finished beer was taken out. A process way more efficient that traditional fermentation.

Briggs described the potential benefits:

there was real hope for the commercial success of continuous systems with the advantages comprising:

•    lower capital cost
•    lower working capital because of less beer in process, as a result of faster throughput
•    lower product cost as a result of lower beer losses, more ethanol and less yeast
•    lower fixed costs because of less manpower as a result of less cleaning and automatic
•    fermenter control.

The first attempts were made in the late 19th century and several different systems were tried in early years leading up to WW I. None proved to be a commercial success. One system involving beer moving from one open tank to another was revived in the 1950s, with experiments in the UK, Canada and New Zealand. It was in the latter two that these trials were put into practice in the 1960s.

In the UK, the process was championed by L.R. Bishop, who worked at the Watney brewery in Mortlake. He seems to have dedicated a good chunk of his career to developing the process, starting in 1925 when he was a post-graduate student. But it was only after WW II that his interest was able to take practical form, in the shape of a 1,000-gallon pilot plant. When this proved a success, a 1,000-barrel plant was constructed.

By the early 1970s, Watney had the system installed in four of their breweries: Mortlake, Mile End, Drybrough and Murphy. Between them, they were capable of producing 20,000 barrels a week. Or around a million barrels a year.  Which was around 22% of their total output.  The bulk of this capacity – 13,000 barrels per week - was at Mortlake.

At its peak in the early 1970s, around 4% of UK beer was brewed using one of the continuous fermentation systems.  Though much of that seems to have been at Watney. With their capacity equivalent to 2.7% of UK production.

I’d always laboured under the assumption that the main reason for dropping continuous fermentation was because the beer produced using it 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.)

Yet, in the late 1970s and early 1980s, most 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 was big advances in cylindroconical technology, speeding up batch fermentation and providing a more flexible method of fermentation.