Sunday 8 May 2011

Koch's postulates in your pint

During my continuing research into brewing with Brettanomyces I found a very interesting paper from 1904. No prizes for guessing the person that put it online.

In the paper Claussen describes how he has isolated the yeast responsible for the "remarkably fine flavour" of English stock beers, and goes on to say how it can easily be proved:

"If we add to pasteurised beer a slight portion of a Brettanomyces culture in wort (say a few drops to a bottle of the beer), and if we then leave the beer to stand in well-corked bottles at a temperature of 75 -80 degrees F during 10 -14 days, a slight deposit will be observable and at the same time the beer will assume an unmistakable English character, both in regard to its content of carbonic acid gas and to its taste and flavour"

Now are you thinking what I'm thinking? Because to me it looks very much like he's applying Koch's postulates to beer. Koch's Postulates are a wonderful bit of science, and as Claussen said in this case very easy to apply.

So I found some bottles of strong pasteurised beers. The first beer I chose was Fuller's Golden Pride as I've drunk a fair bit of it in my time. Back in the days when Safeways was around for some reason it was cheaper than London Pride so how could I resist? In fact it was entrapment if you ask me.

I also got some Robinson's Old Tom as I've heard it's to a very old recipe so might well have had the benefit of Brettanomyces back in the day.

Next I took a liquid culture of Brettanomyces claussenii and inoculated 1 ml of it into the bottles. I'd popped the tops off and let them stand for a few hour to de-gas a bit first as I didn't want them to be over carbonated. Once inoculated I re-capped them and put them in the airing cupboard for a fortnight.

When I came to open the bottles it was with some trepidation. Would I have terrible gushers? Or would I have a damp squib with no noticeable difference? As it happens the carbonation level was fine and there was a detectable difference in the taste. This is no time for sound bites but I felt the hand of history upon my tongue.

The Golden Pride had dried out and lost a lot of the excessive sweetness. There was a slight unusual taste (or should that be unmistakable English character?) that must have come from the yeast. None of that horse blanket malarkey mind, but definitely something a bit different, and the beer was dangerously drinkable. The difference was less apparent in the Old Tom, but again it was drier and with that slight unusual taste.

If I was half the scientist Robert Koch was I'd have had a control sample, and taken some measurement such as pH and gravity, as well as writing proper tasting notes. So I'm trying to remedy my short comings by repeating the experiment with more rigour. Further results to follow.


  1. I'm sure you will have said somewhere on anouther post, but where do you get the Brettanomyces from?

  2. I got it from a home brew shop, but it was horribly contaminated. I can send you a purified culture on a slope if you're interested.

  3. The dryness that Brett brings can really work in certain beers. I tried a Mikeller beer once brewed purposefully with Brett. Driest beer I have ever tasted.

  4. That is a very kind offer Ed, I'd be very grateful if you did send me a slope.

  5. I'm subculturing the Brett on again soon Dave, so I'll send you a slope up in a fortnight or so.