The answer to the question is, as they say, somewhat complicated. One of my favourite recipes in my cookbook, the Canadian Craft Beer Cookbook, is not really a recipe at all. It’s more of a process – three in fact – for turning good beer into excellent vinegar.
I go through the why’s and how’s in some detail in the book, but the short version is something like this: just as there is a microbial action that converts the sugar in wort to the alcohol and carbon dioxide in beer; there is also one that further metabolizes that alcohol into acetic acid. Different microbes and different results, but they are similar.
There are a few ways to introduce the acetic-acid-causing bacteria to the beer. The simplest is by mixing in a small amount of the “mother” from a bottle of unpasteurised apple cider vinegar.
Usually, it is in everyone’s best interest to keep the vinegar making reaction at bay. Brewers package their product in airtight containers to exclude oxygen and keep the acidifying process from happening. I’m not one for usual, so this idea that I can make a variety of homemade vinegars from leftover beer is pretty captivating.
Before submitting the manuscript for my book, I tested the process five or six times to learn what worked most reliably. After some reflection, I see that I still have a few questions. The purpose of today’s post is to share those questions, my early hypotheses, and seek feedback from you guys.
How much does the source beer’s ABV matter to its vinegar making potential?
I don’t know why I put this question first because I suspect it will be the most difficult to answer. On one hand, alcohol has an antiseptic quality – no matter how long you leave it exposed to oxygen rum, as far as I know, will never turn to vinegar. On the other hand, the acetobacter is converting alcohol into acid, so doesn’t it make sense that more source material means more product?
How much do the component flavors in the source beer transfer through to the vinegar?
I plan to pay particular attention to hop, malt, and yeast characteristics. My guess is that because they are the least delicate and most closely associated with flavor rather than aroma, the malt characteristics will stick around after the others have faded.
What about adjunct beers? Does pumpkin beer make pumpkin vinegar? Do spiced beers give that particular flavor to the vinegar?
I have no solid hypothesis here.
What impact does the vinegar making environment have on the final product? Specifically light, ambient temperature, and humidity.
So far, I’ve had to fight against evaporation (by adding filtered water) as an undesirable, coincidental process, so I imagine that low humidity and/or high temperatures are non-optimal.
Sunlight quickly reacts with some of the oils derived from hops to create undesirable, skunky aromas. Will these dissipate or be overwhelmed by the other flavours if the proto-vinegar is exposed to light?
What else can go wrong?
A vinegar mother is a semi-solid mass that usually floats midway in the vinegar or sinks to the bottom. If it floats to the top or enough liquid evaporates, I’ve noticed that it can support mould, which is a bad thing.