Fermenting fall

This fall has stricken me with fermentation fever, and my kitchen has turned into a laboratory run by yeasts, bacteria and various enzymes.

It happens every year. That’s because autumn culminates in an explosion of fruit—fruit that draws laden tree branches toward the Earth and eventually carpets the ground. Thanks to friends with productive trees, I have been able to fill buckets with apples and pears from Sebastopol, cactus fruits from San Rafael, figs from Novato and more. This prolific season never fails to awe me. It serves as a vivid reminder of plants’ amazing capacity to produce sugar from carbon dioxide, sunlight and water.

For homebrewers like me, it’s a chance to coax the same natural processes forward a step or two and, in a controlled space, turn nature’s sugar into alcohol and acid, and put it in a bottle.

The generous bounty of a neighbor’s Asian pear trees got me fired up in September. The owner said he was “all pear-ed out” and welcomed a friend and me to take all we wanted. We harvested more than 100 pounds of yellow and brown Asian pears from several trees, leaving at least five times that behind. At home, we ground the fruit into pulp and pressed it to render juice. Some folks might have halted the process there by freezing the product, but the homebrewer in me wanted to ferment it.

So, we let the pear juice—delicious as such, I must say—start transforming into an alcoholic nectar. We added no yeast, allowing natural yeasts to do the job. Unfortunately, the juice turned sour as it fermented. It also grew thick and syrupy, and developed a coating of white scum on the surface—a harmless but annoying pest known as kahm yeast.

Not ready to sacrifice 8 gallons of summer’s liquid sunlight, I drummed up a solution: Add bacteria and see what happens. We divided the batch in two. One we reserved as the control batch, while in the other we dumped a scoby, aka “symbiotic culture of bacteria and yeast.” A scoby is what’s used to create kombucha from sweetened tea. Plop! The slimy scoby disappeared into the froth, and it’s been working on the brew ever since. I have not yet tasted it.

For weeks, the control batch has remained sour, and there seemed just one way to salvage the other half of the juice: make vinegar. So, we added a vinegar mother, cultured from the dregs of a bottle of Bragg’s apple cider vinegar—because if you can’t beat sourness, make more of it.

Then we turned our attention to apples, dropping by the thousands from neighbors’ trees, and once again, out came the grinder and the juicer. We made about five gallons, planning to make cider vinegar and boozy kombucha.

When the pineapple guavas, or feijoas, on my parents’ tree in San Francisco began dropping in October, I picked the fragrant green fruits off the ground with each visit home. By early November, I had 15 pounds in my fridge. I experimentally juiced a few of them and added the liquid to a batch of kombucha. Impressed, I made more—2 1/2 gallons, to be precise.

Meanwhile, I donned leather work gloves to harvest nearly 100 rosy-red prickly pears—called tunas, in Spanish—from a suburban cactus in San Rafael. I made juice to flavor another batch of kombucha.

The harvest season is nearing its end, and perhaps, that’s just fine. My kitchen has no room left for more bottles of fermenting and acidifying juice. The persimmon have yet to ripen, and citrus season is just starting, but for the most part, 2019 is all bottled up.