Recently I’ve been reading a book called “The Home Brewer’s Answer Book” by brewer extraordinaire Ashton Lewis. This book is aimed at homebrewers and provides a resource for them to consult when things start to go wrong with their beer. I’m finding it to be a great source of info on beer in general, and a wonderful source for learning about the science behind beermaking.

As I’ve flipped through the pages, I’ve come across a few nuggets of info that would have nicely fit into a couple of my past articles. Rather then go back and rewrite them, I thought I just post the new follow-ups here.

Two of my first beer cellar science postings had to do with the buttery-tasting molecule called Diacetyl (Beer Cellar Science: Diacetyl Part 1 and Beer Cellar Science: Diacetyl Part 2). In the Answer Book, I learned that yeast do not actually produce diacetyl, instead they produce a precursor molecule to diacetyl called alpha-acetolactate. In the presence of an oxidizing compound (iron, copper, or most often oxygen) alpha-acetolactate can be catalyzed into diacetyl. I had always thought diacetyl was released directly by the yeast, so this was pretty interesting stuff to read.

In my articles on bottle-conditioning (Bottle Conditioning Part 1 and Bottle Conditioning Part 2) I wrote about the process of autolysis and how it can affect your brew. It turns out that various enzymes called esterases and proteases are released into your brew as the yeast cells decompose. These esterases will help break down any fruity-tasting ester molecules they come in contact with, and are a big reason why fruity flavors diminish in time in aging beer. The proteases will bust up the foam-stabilizing proteins in your beer, which is why your vintage brew may not have as vigorous of a head as a fresh beer has. Good stuff!

I’ll be sure to post more on the subjects as I come across more info. I’m such a geek.

Jason

jason@brewbasement.com