In a large non-reactive container, stir malt extract into 3 quarts of bottled drinking water (do not use tap water! there are chemicals there that might kill fermentation process).
Step 2: Fermentation
Dissolve rye sourdough starter in 1 cup of diluted malt mixture, stir, and pour it into the pot.
Keep at room temperature (72-74F) for about 2 days. It takes 12 hours when the temperature is 86F. At lower temperatures, fermentation process takes longer.
In 12 hours, 72F, the surface of kvass will be mostly covered with thick layer of foamy bubbles. Your kvass is ready to bottle when its taste is pleasantly sour, with an appetizing aroma.
Prepare two pint-sized clean screw-cap or flip-top bottles and funnel.
When bottling kvass, make sure the sediment on the bottom of the jar where kvass was fermenting is not disturbed. To carbonate kvass during the next step, conditioning, feed it with agave syrup right before bottling. Add 2-3 small raisins per 1/2 quart of kvass. Seal the bottles.
Step 3: Conditioning
Condition bottled kvass at 45-50F temperature for at least 3 days or up to 7 days (wine refrigerator is the best).
After conditioning, store bottles refrigerated. It is good for drinking for the next 2-3 weeks. The longer it is stored, the more tartness it will develop, because it's alive. By lowering down the temperature, we only slowed down the fermentation, we didn't stop it. Keeping bottles upright helps to clarify kvass.
Experimenting with Kvass in TexasDo not use yeast only — you'll get a beverage with much higher level of alcohol and unpleasant aroma (been there done that!). If you bake your own bread, start making your kvass when you have 1-to-3 days old dough in your refrigerator. If you don't, buy a portion of sourdough starter in your favorite bakery.The sediment on the bottom of the jar where kvass was fermenting can be used as a kvass starter. It is not safe to use it for more than 2 to 3 batches. When using kvass starter, plan in advance. Have your next kvass bread extract ready by the time your currently fermenting kvass is ready to be bottled.A good seal is needed to withstand the pressure build up in the bottle that gives the beer it's carbonation. I use flip-top beer bottles. The rubber seal of flip-top bottles can't hold the pressure over long periods of time. They are good enough to condition kvass for a few days, easy to clean, and you will never loose the flip-top. The rubber seals can be replaced over time. These bottles are cheap and easy to find. For a couple of bottles, look for good deals online or in Home Goods/TJ Maxx/Marshals/Hobby Lobby, etc. Since kvass is conditioned for a relatively short time period, dark glass is not important. My favorite sugar and flavoring ingredient is D-180 Candi Syrup. It can be found in many beer brewing supplies stores.Fermenting Veggies at Home: Follow Food Safety ABCs Food fermentation: a safety and nutritional assessment Fermented foods and food safety