The science of kvass

[bernardsmith]

I am trying to make sense of kvass.
When I brew beer from grains I
1) mash the grains to transform the carbohydrates of the grains into simpler sugars through the action of enzymes in the mash and
2) the enzymes are present through the earlier germination of the grains. Under normal growing conditions these enzymes would allow the plant to feed of the grain seed to derive the energy it needs to grow and develop.

Kvass, however, is made from bread (or flour). Bread is not made from germinated grains. Traditionally, kvass does not include any additional sugars. Traditionally kvass may ferment to about 2% ABV.

What is fermenting if we use a beer or a bread yeast to make the kvass? In other words, how does ‎S. cerevisiae ferment complex sugars if we have not added any enzymes? And if the ‎S. cerevisiae is not fermenting the carbs is it lacto bacteria that are doing the work? And if kvass is a sour beer why do most recipes suggest that ‎S. cerevisiae be added? And if the ‎S. cerevisiae can get at sugars in the bread and ferment them what is the reason for malting grains

 

[hunter_le five]

All of the bread kvass recipes I've ever seen also called for adding white sugar, honey, or both.

 

[bernardsmith]

All of the bread kvass recipes I've ever seen also called for adding white sugar, honey, or both.

I am sure that they do... but that is not a traditionally made kvass... Kvass is considered a soft drink although it does have some alcohol content.. And I have made kvass with and without additional fermentables.. My question was not how can kvass be made more fermentable but what is the science that under girds the traditional method of making kvass? Is it really a sour beer or is it an S. cerevisiae fermented beer and if the latter where do the enzymes come from?

 

[hunter_le five]

I am sure that they do... but that is not a traditionally made kvass... Kvass is considered a soft drink although it does have some alcohol content.. And I have made kvass with and without additional fermentables.. My question was not how can kvass be made more fermentable but what is the science that under girds the traditional method of making kvass? Is it really a sour beer or is it an S. cerevisiae fermented beer and if the latter where do the enzymes come from?

Perhaps, but they all sure purported to be "traditionally made kvass" recipes.

And I wasn't telling you how to make it more fermentable; I was suggesting that maybe the bread doesn't contribute much in the way of fermentables, but rather that maybe it was the addition of sugars.

Again, as I browse the interwebs, I am having trouble finding a bread-kvass recipe that does not list sugar as an ingredient.

But perhaps there is some enzymatic action that converts the bread into simple sugars as well. Maybe something in the yeast? Wild bacteria from the air. No idea.

 

[hey.ryanm]

I am sure that they do... but that is not a traditionally made kvass... Kvass is considered a soft drink although it does have some alcohol content.. And I have made kvass with and without additional fermentables.. My question was not how can kvass be made more fermentable but what is the science that under girds the traditional method of making kvass? Is it really a sour beer or is it an S. cerevisiae fermented beer and if the latter where do the enzymes come from?

I am currently at the same question as you were in 2015. Have you found any more information on this?
I'm gearing up to do myself a Kvass-style beer and use my Sourdough Starter as the yeast and let it ferment all the way through.
I want to keep it tradition and not add any other grains and keep the base 100% wheat from old sourdough bread.
Seems like most recipes that don't add other grains cut the fermentation short and keep it low abv and soda like. While others that make it in a home-brew style add other grains. I have yet to find any information on a 100% bread kvass home brew "beer". But what is the difference between a 100% wheat beer? From my understanding my Sourdough Starter is capable of converting the starches into sugars to ferment- which is what is happening when making bread since the raw flour itself has very little sugar. I'm just unsure how this works when the flour isn't raw and it's already baked.
Is there a way to properly"mash" the bread, or if it's even needed. Most recipes pour boiling water over the toasted bread pieces and keep covered for 24 hours but then they always add extra sugar like you said. I think traditional Kvass just wasn't fermented long enough to become more than 1%abv but I'm also thinking they used a yeast that had the enzymes to convert the starches from the bread that in theory cut out the need for added fermentable sugars. Let me know if you ever found anything out!

 

[FlyingAxe]

I am currently at the same question as you were in 2015. Have you found any more information on this?
I'm gearing up to do myself a Kvass-style beer and use my Sourdough Starter as the yeast and let it ferment all the way through.
I want to keep it tradition and not add any other grains and keep the base 100% wheat from old sourdough bread.
Seems like most recipes that don't add other grains cut the fermentation short and keep it low abv and soda like. While others that make it in a home-brew style add other grains. I have yet to find any information on a 100% bread kvass home brew "beer". But what is the difference between a 100% wheat beer? From my understanding my Sourdough Starter is capable of converting the starches into sugars to ferment- which is what is happening when making bread since the raw flour itself has very little sugar. I'm just unsure how this works when the flour isn't raw and it's already baked.
Is there a way to properly"mash" the bread, or if it's even needed. Most recipes pour boiling water over the toasted bread pieces and keep covered for 24 hours but then they always add extra sugar like you said. I think traditional Kvass just wasn't fermented long enough to become more than 1%abv but I'm also thinking they used a yeast that had the enzymes to convert the starches from the bread that in theory cut out the need for added fermentable sugars. Let me know if you ever found anything out!

If kvass made solely from bread and S. cerevisiae does ferment, then certainly the yeast is finding a source of sugar. I have a hypothesis that might answer your conundrum:
the action of wheat/rye amylase. Most flour has a small proportion of amylase, although refined wheat flour doesn't contain much of it; lab-produced amylase or diastatic malt extract are indeed used in baking to improve this low amylolytic activity inherent to flour. After all, even the simplest bread dough (salt, water and flour) rises with pure yeast strains and without any added sugar or enzymes, thus there must be some conversion of starch to free sugars happening. Granted, you don't need all that much fermentation to rise dough compared to getting a 5% ABV brew, but if enough of these free sugars remain in the bread after baking, it could be used to ferment into alcohol in the kvass, perhaps just enough to carbonate it or even to push it to 1%.

I also considered the contribution of microbial amylase from sourdough. There are definitely strains of Lactobacilli that produce amylase, and although I am far from an expert on rye bread making, a bit of reading seems to indicate that you'd actually want to slow down amylase activity in rye bread to get a nice spongy bread. Which means that maybe a bread that turned out crumbly from poor management of rye amylase would actually make better kvass? That would make for a nice origin story to the mysterious brew

In any case the chemistry of sourdough rye bread is more complicated than I care to read about at this time but it might be something worth investigating to understand when and how the starches are converted during the fermentation process, and how that enzymatic conversion is halted to get the right balance of free sugar and crumb structure.