The second beer I brewed over the Labour Day weekend was a pale sour inspired loosely by the practices of Belgian lambic makers. I say loosely because I did not perform a turbid mash, and I pitched a vial of ECY01 rather than allowing the wort to be inoculated by ambient microbes. But I did try to produce a starchy wort by other means, and its that process that I want to describe in this post.
The basic idea is to add some starch to the wort at some point after the enzymes from the mash have been denatured, so that this starch is not broken down and makes its way into the fermenting beer; while the Saccharomyces will be unable to ferment it, the Brettanomyces and other bacteria are capable of breaking the starch down into sugars and eventually fermenting it out.
I first got the idea to do this from an interview with Dave Marliave of Flat Tail Brewing on this episode of the Sunday Session . In the interview, Marliave describes adding flaked oats to wort post-boil to mimic the starchy wort produced by the turbid mash that lambic brewers use. He states that these starches take much longer to breakdown and ferment out than other complex sugars, so that the overall effect is to prolong the lifecycle of the beer. It might mean, for instance, that a sour brewed in this way still had some residual sweetness and body a year or two into fermentation, and might continue to develop over a longer period. So the idea here is not just to provide food for the bacteria so that they produce enough acid (this might also be achieved by mashing high or adding maltodextrin); its to extend the life of the beer, and change the way its flavour profile develops over time.
The method I use is a variation of the one that Marliave describes. After I've raised my mash to mash-out temperatures and removed the bag with the grist, I add another small mesh bag filled with between 100-200g of flaked oats. I steep these in the wort for five to ten minutes while I bring it up to a boil, then remove them and give the bag a quick squeeze. The result is a very cloudy and turbid wort, as you can see from the photo at the start of the post.
When I first heard the interview, I started this thread on HBT to see if other people had used the technique. If you browse through it, you can find links to other people trying the same kind of thing: some use flaked oats, others add flour to the boil. This episode of Basic Brewing Radio includes an interviewer with a home brewer who adds pasta to her secondary fermenters with the same goal in mind.
This is the second time I've used the process. The first beer I brewed is around nine months old at this point, and I took a quick sample this week before writing this post. So far, the results are promising, and in line with what Marliave describes. The beer is still a bit turbid, but has cleared considerably over the course of the year. I have no way of knowing how much of this is breakdown of starches and how much precipitation of proteins etc. The aroma was mainly lemons and light funk, and the beer tasted lightly sour with some noticeable residual sweetness and body. At this point it is not a particularly exciting beer, but at nine months old its still relatively young, and I plan on leaving it for at least another six to eight months before I even think about bottling it.
The two batches I brewed this weekend were based on a fairly straight-forward lambic style wort: 60% pilsner and 40% malted wheat. A few months ago I went through my freezer and took out a bunch of hops from the 2011 harvest and earlier and put them in a brown paper bag in my brew closet to speed up their ageing. They could probably used a few more months, but I decided to use 30-40g per batch anyway. Since I was not relying on inoculation from ambient microbes, I didn't need the bacteriostatic properties of the hops to check unwanted bacteria. But there's some evidence that fatty acids and other products of oxidation in aged hops can be converted by brettanomyces into the ester compounds characteristic of aged sour beers (see p.42 of American Sour Beers for brief discussion of this research), and that seems like reason enough to try using them.
Once primary fermentation is over, I plan to combine 5 gallons in a Better Bottle, which I may end up treating as another solera. The remaining gallon or so will be aged in jugs, but I plan on blending it with another saison in a few months and then letting this mature for a year or so.