For Carolingia's Baronial Investiture event (June 8, 2002, AS 37), I was asked to produce kvass to be served with the Russian course. My research started with surveying some available recipes. The only period recipe that I know of is from the Domostroi, a 16th century Russian household handbook. The notes I have are from the translation made by Carolyn Johnston Pouncy, published by Cornell University (1994, ISBN 0-8014-2410-0):
In chapter 29: Similarly, she (the wife) should know how they (the servants) make beer, mead, vodka, weak beer, kvass, vinegar, and sour cabbage - every liquid normally used in cooking and breadmaking.
In chapter 36: A women should drink either weak beer or kvass, both at home and in public.
In chapter 42: In a well-ordered home you can find (animal) feed in either summer or winter: dregs of beer, vinegar, kvass, and sour cabbage soup.....
In chapter 52: The steward should measure and record amounts of bread, rolls, beers, vodka, ale, kvass, sour cabbage, vinegar, siftings, bran, dregs of any kind, yeast, and hops.
In chapter 54 (which is titled "How to Preserve Food in the Cellar and the Icehouse"): There you should also store cucumbers, pickled and fresh cabbage, turnips, other vegetables. . . apple kvass, bilberry juice, Rhenish wine, vodka, mead, fermented and unfermented beer, and ale.
In chapter 65: Ordinary kvass. To brew ordinary kvass, Take four parts honey and strain it until it is clear. Put it in a jar and ferment it using an ordinary soft loaf, without additional yeast. When it is done, pour it into a cask.
In chapter 67 (wedding rituals), on setting up the groom's and bride's room: A sideboard stands nearby, holding a dozen mugs containing different drinks made from mead and kvass.
A very refreshing Russian beverage which is made in many Russian households about once a week.
With eight quarts water take 1 1/2 lb. malt, 1 lb. rye flour, 1 1/2 lb. sugar, 1/8 of a lb. mint leaves, half pepper pod, and half cake of yeast. Mix the malt and flour with boiling water and make a thick dough. Put into barely warm oven, and leave for the night. Next day dilute dough with eight quarts boiling water and pour into a wooden tub. Let stand for 12 hours, then pass through a cloth. Pour one quart into an enamel saucepan, put on fire, add 1 1/2 lb. sugar, and an infusion made with the mint leaves (resembling weak tea). Boil once, then take off fire, cool until just warm, and add the yeast previously diluted with one cup of this same warm liquid. Let stand in warm place until it begins to ferment; then pour it into the rest of the kvass in the wooden tub, and let stand until bubbles appear. Prepare clean bottles, putting one malaga raisin into each; pour in the kvass, cork the bottles, tie the corks with string to the necks of the bottles, and keep in a warm place for a day or two. Then put in a cold cellar.
To prepare 5 liters of bread kvass, dilute in warm 35-40 deg C water 10 tbsps of syrup, 1 2/3 cup sugar, 6-7 g of pressed yeast, keep 25-30 deg C 18-20 hours. Chill, filter, store in a cool place.
(I included this in my research primarily to help determine the proper level of sweetness.)
Kwass (Yield: 6 cups)1 lb. day-old black bread or Danish pumpernickel
Dry the bread and then chop it into coarse pieces. The add the bread to six quarts of boiling water, remove from heat and cover with a towel. Set aside for eight hours. Then strain the mixture through a fine sieve into another large pot, extracting as much liquid from the bread as possible. Discard the bread. Add the yeast and 1/4 tsp. sugar to the lukewarm (110-115 F [43-46 C]) water and stir thoroughly. Set this aside for about ten minutes in a warm place and then add the yeast mixture, the remaining sugar, and the mint [to the bread-water], cover again with a towel, and set aside for about another 8 hours. Strain the mixture again and bottle in a gallon jug or several quart-size bottles. Fill the bottles 2/3 full, then divide the raisins evenly among the bottles. Cover each bottle with plastic wrap secured with a rubber band. Place in a cool spot for three to five days, or until the raisins rise to the top and the sediment sinks to the bottom. Carefully decant the clear amber liquid [picking out the raisins?] and rebottle in clean bottles. Refrigerate until ready to drink.
Ingredients: (for 6 cups)1 pound day-old black bread or Danish pumpernickel
Preheat the oven to 200F. Place the bread in the oven for about 1 hour, or until it is thoroughly dry. With a heavy knife, cut and chop it coarsely. Bring 6 quarts of water to a boil in an 8-quart casserole and drop in the bread. Remove from heat, cover loosely with a kitchen towel, and set it aside for at least 8 hours. Strain the contents of the casserole through a fine sieve set over another large pot or bowl, pressing down hard on the soaked bread with the back of a large spoon before discarding it. Sprinkle the yeast and 1/4 teaspoon of the sugar over the 1/4 cup of lukewarm water and stir to dissolve the yeast completely. Set aside in a warm, draft-free spot (such as an unlighted oven) for about 10 minutes, or until the mixture almost doubles in volume. Stir the yeast mixture, the remaining sugar and the mint into the strained bread water, cover with a towel, and set aside for at least 8 hours. Strain the mixture again through a fine sieve set over a large bowl or casserole, then prepare to bottle it. You will need 2 - 3 quart-sized bottles, or a gallon jug. Pour the liquid through a funnel 2/3 of the way up the sides of the bottle. Then divide the raisins among the bottles and cover the top of each bottle with plastic wrap, secured with a rubber band. Place in a cool -- but not cold -- spot for 3 - 5 days, or until the raisins have risen to the top and the sediment has sunk to the bottom. Carefully pour off the clear amber liquid and re-bottle it in the washed bottles. Refrigerate until ready to use. Although Russians drink kvas as a cold beverage, it may also be used as a cold-soup stock in okroshka (chilled vegetable soup with meat) or botvinia (green vegetable soup with fish).
Add yeast and one tbsp of flour to 1/4 c. warm water. Mix the flours together. Dilute the malt in some hot water, then add to the flour with two pints of the water above. Stir well, getting out all the lumps. Allow to stand 5 hours. Then blend in the rest of the water, the yeast and the mint. Allow to ferment for twelve to twenty-four hours then strain and bottle.
Black Bread Kvass1 1/2 pounds stale black bread, cubed
Place the bread cubes on a baking sheet and toast in a 325 degrees oven for about 20 minutes, or until dry. Transfer to a large crock. Sprinkle the mint over the toasted cubes. Add the lemon. Pour the boiling water over all, and cover the crock tightly. Let stand 5 to 6 hours. Strain the liquid through cheesecloth, pressing down on the bread with the back of a spoon in order to extract as much liquid as possible, but with out pushing sediment through. To the liquid add the sugar, the cream of tartar and the yeast, which has been dissolved in a little of the liquid. Stir well to mix. Cover the container, let stand undisturbed for 8 hours. The next day, strain once more through cheesecloth and pour into a 1-quart bottle. Add the 8 grains of rice. Seal. Let stand for 8 hours more at room temperature. Then strain once more through cheesecloth into a clean bottle and refrigerate until ready to use. Yield : 1 quart
Armed with all sorts of knowledge on kvass, none of it precisely what I needed, I set to work. I started by buying a 5lb sack of rye flour and making bread, and tried out several variations. Specifically, I tried with and without mint and raisins, whether to toast or dry the bread beforehand, how much sweetener to add, whether that sweetener should be sugar or honey, how thoroughly to strain the liquid, when to do this straining, what sort of yeast to use, and how long to ferment the liquid.
Using mint and raisins changed the color (I had dried mint on hand), and wasn't particularly better, and didn't seem to follow the period model, so I decided not to add them.
Toasting the bread gave a "deeper" tone to the drink, as well as a bit of "burnt" flavor. Working with fresh bread resulted in less flavor being extracted into the water. There seems to be a better etymological for using non-toasted bread, though many modern recipes employ toast. In the end, I decided to go with dried but not toasted: it seems reasonable that this would have been a way to use up old bread, and I got more bread flavor in the drink that way.
As the period sweetener would have been honey, I choose that over sugar.
As I was looking to make a less-than-0.5% alcohol beverage (so it could be served at a dry site), I took a minimal fermentation time of eight hours.
The issue of straining proved the most challenging. If I put the bread in water, then sweetened and added yeast, then when the overnight fermentation was done, the bread particles would be impossible to remove. Furthermore, when the bottles were later opened, any settling would be obliterated by the resultant foam. To avoid these 'sludgy bits', I had to soak the bread, then siphon off the clear liquid, and ferment that. The problem is that the former was both tastier on some accounts, and likely to be more period. In the end, the latter method won out, partly out of concern that people would find it too strange otherwise, but mostly because the people trying this would require their glasses for other beverages afterwards.
I tried bread yeast and wine yeast, and found that the bread yeast yielded a fine product, and as it seemed more authentic, went with that.
Take a pound of rye flour, add water and yeast to make dough, let it rise, and bake it. This is a very basic rye bread. It will be quite dense, and probably suitable for making melba toasts. Cube the bread, and set it out on trays to dry. This may take a day or two, depending on the humidity.
Take a loaf-worth of dried out rye from Part I, and put it in a jar. Boil two quarts of water, and pour it over the bread. Cover and let sit 8-12 hours. Agitating it after has cooled to lukewarm, and again 1/2 hour before the end, helps more of the bread-ness to get into the water. Take a siphon hose and siphon off the clear. You should get almost a quart of liquid per loaf. Try to avoid even the white layer between the sediment and the clear, but don't worry overmuch if you get some. If you are doing this in stages, you may refrigerate this liquid while you await the completion of other batches.
Take the liquid from Part II and add honey per quart of liquid. Put the liquid in a vessel with a vapor lock, proof bread yeast and pitch it in, and let it sit eight hours. Then put it in bottles and put them immediately in the refrigerator. Only remove them to serve or transport, transport packed in ice. When you open the bottle, do so angled downward over a large container -- it will make a lot of foam. Allow a minute for the excess foam to dissipate.
You get a lot of rye sludge as a byproduct. This can be used as gruel, or simply tossed (especially if it is lumpy). It may be better to add the honey (in greater quantity) to the initial water; I added it later to save on costs. You can expect to spend similar amounts on flour, yeast, and honey if, as I did, you get the flour in 5 lb sacks and the yeast in 4 oz jars. I spent $80 on consumed supplies making 10 gallons. I'm happy to report that kvass was the surprise hit of the feast -- people really enjoyed it. I hope that your experience with kvass is as pleasant.