Amazake Vinegar

Another way to turn scraps into gold

Sugar is the precursor to vinegar. It needs to be dissolved in water, in concentrations high enough that yeast can create sufficient alcohol (10%, give or take a few points) for bacteria to convert into acetic acid. That’s the essence of it: a two-stage ferment. You can read our Vinegar 101 primer for more detailed info and methods. Where your sugar comes from is a (probably the) major determining factor when it comes to the fundamental character of your vinegar. Let’s stipulate here that we’re talking about making vinegar from scratch, not using existing alcohol like leftover wine.

Sugar obviously works, in all its forms, as do honey and maple syrup and apple (and other fruit) juices. If you read our amazake post, or have worked with koji’s sweeter side at all, you know that our favorite mold’s enzymes break carbohydrates down into their component sugars. Make a slurry of koji and cooked rice and water, let it sit for a few days, and you’ll have a sweet, aromatic porridge: amazake. This form of sugar is the basis for just about all of East Asia’s alcohols, like sake, soju, shochu, baiju, and more.

This is also how a lot of Asian vinegars are made, and that’s what the jar up top was a precursor for. The photo is of a purple sweet potato amazake from last summer. It’s hard to believe that color, right? I used the standard ratio of 1:1 koji rice to baked sweet potato peel (just the peel; I ate the potato) and 2 parts water. If you leave this out at room temp for a few days, it will become quite sweet as the koji enzymes convert the rice and sweet potato starches into sugars. At the same time, though, it will also begin to ferment as bacteria and yeast eat those sugars and starches. So soon enough it’ll start to sour, reducing your sugar content.

The easiest way to avoid any premature souring is to accelerate the enzymatic reactions with temperature. I use an immersion circulator in a water bath set for 140˚F/60˚C, and leave the jar submerged in that for about 24 hours. This temperature catalyzes the enzymes, making them work much faster than they do at room temperature. Because it’s also at the low edge of what’s known as the “safe zone” in food safety parlance, it effectively prevents any microbial activity because it’s too hot for yeast and bacteria to survive. So you get something like a week’s worth of starch conversion in one day, and no souring to diminish the sweetness.

Then you can strain out the solids and set your liquid up to become a vivid pink vinegar (in this case; you can use orange sweet potato or regular potato peels too). I didn’t have a ton of the liquid, since this was just made for the peel of one sweet potato. But happily I had a batch of tepache that had gone past the point where I like to drink it, getting very tangy and acetic in the warm weather. Perfect! I combined the two and put them in a half-gallon jar in a corner of my kitchen with an old cloth napkin secured over the open top with a rubber band. Now, about 6 months later, it’s a delightful vinegar—orangey-pink, full of fruity nuance (purple sweet potatoes have all sorts of lovely tropical notes) and a long, complex finish.

So you’ve got potato peels on one hand and pineapple skin on the other: both byproducts, both easily transformed via enzymes and microbes, joining forces to make a gourmet-quality vinegar with real depth and resonance. If that doesn’t sum up why we’re all here, I don’t know what would.