My son is a beer geek and quite the talented homebrewer. We both enjoy getting and tasting unusual beers from around the world, and can boast about more than 200 different styles that we have tasted.
We took a particular interest in lambic beers last year, mainly because they are spontaneously fermented using yeasts and lactobacilli from the local atmosphere, very much in the same way sourdough bread is created. This means that there are no live yeast isolates added to the brew. This is a long process, taking usually up to 2 years.
Explaining biological fermentationAs many people don't know the air is full of yeast spores and bacteria. Different strains of micro-organisms have different affinities for nutrients. It just so happens that a few strains have strong affinities to specific carbohydrate molecules, such as in the maltose found in barley malt (beer) and wheat.
What happens in sourdough and in lambic beers is that a symbiotic relationship develops in the culture medium between a single strain of yeast and a single strain of lactobacilli. Basically the lactic acid created by the bacteria renders the medium inhospitable to most other micro-organisms with the exception of a specific yeast strain, that can tolerate and thrive in an acidic environment. (Greenwood, 1996)
Commercial brewing and baking yeasts are grown in conditions where there is no contamination by bacteria, and their activity is so fast (especially in bread baking) that there is very little contamination during fermentation. Brewing beer is another story, and risk of airborne bacteria contamination is very high and can introduce all kinds of unpleasant flavors. This is due to the complexity and the ongoing transformation of the available carbohydrates in the mash that will attract a wider variety of bacteria strains. This is partially controlled by the initial pH of the mash that helps not only the transformation of fermentable sugars but renders the environment inhospitable to unwanted bacteria.
As many sourdough bakers know, the location that the culture comes from creates bread with unique flavours. Many people agree that San Francisco sourdough bread is the best tasting (although a French Poulain loaf is my personal favorite), and in fact a unique strain of bacteria has been isolated and named for it (
L. Sanfranciscans), with the dominant yeast strain being the common
C. Milleri. Other sourdough types will have a variety of yeast and lactobacilli that may or may not be unique to a region.
Cherry Orchards and Lambic BeersBut what makes the traditional lambic is a really simple trait: they are fermented in or around cherry orchards. This got us to thinking that since the carbohydrate is essentially the same in beer and in bread (maltose), then a sourdough bread culture that was developed in a cherry orchard should be pretty good.
It just so happens that we have 3 very productive bing cherry trees in our back yard. This meant figuring out the optimal time to begin developing a culture. Logically this would be when the carbohydrates in the cherries would be naturally developing yeast and bacteria cultures and releasing large quantities of spores. In other words, when the cherries were nearly fully ripe and showing signs of rot.
Starting and developing the CultureI use and frequently refer to the instructions in the
rec.sourdough.faqs for developing atmospheric cultures and maintaining my existing ones. I basically followed these instructions and expected to get activity in about a week. The cherries on my trees were nearing their peak and we had begun picking at this point.
I was quite surprised to have noticeable bubbles in the culture in only 12 hours. I kept to the schedule, however, with 2 refreshes over a period of 5 days. To be honest it smelled pretty bad, like old cheese, so I was a bit worried this would be a bust. Also temperatures were in the mid 90s, and I was concerned this was too hot for natural yeasts (which die typically around 97 degrees F).
After bringing the culture inside, I followed the instructions for "polluted" culture. This meant taking only a couple of tablespoons of the outdoor culture and adding it to a thin mix of water and flour. This part of the process is called "washing" but it really is about giving the desireable micro-organisms a chance to take over the culture and kill off the undesireable molds and bacteria. I expected to have to go through at least 3 generations of washing out, but was surprised to find the culture was ready after the first wash! Just the same, I repeated the cycle to be on the safe side, and was amazed at how it was developing! Usually it takes about 24 hours for serious activity, but the 1 quart mason jar was overflowing after 12 hours!
After baking with it, I must say I indeed have a winner. The taste is slightly more sour than my San Francisco bread, but this is what I was aiming for.
Greenwood, D. 1996.
What is the Microbiology of San Francisco Sourdough?