Specialty Fermented Breads: Kvass, Rye Sourdough & Soda Bread

Rye is the specialty grain that most rewards a sourdough approach. Where wheat builds an elastic gluten network you can stretch and fold, rye has almost no usable gluten. Instead it’s rich in pentosans — gums that soak up water and turn the dough into a sticky, clay-like paste. You can’t knead rye into a smooth ball, and trying to will only frustrate you.

What holds a rye loaf together is acidity. A well-soured dough firms up the pentosans, controls the enzymes that would otherwise make the crumb gummy, and gives rye its characteristic deep, malty tang. This is why rye is almost always made as a sourdough rather than with commercial yeast — the sour is structural, not just flavour.

Rye holds a lot of moisture, so it needs a long, thorough bake — use a thermometer rather than the clock and check the internal temperature guide. Then comes the hardest part: wait. A dense rye loaf needs up to 24 hours of resting before slicing so the crumb can set. Cut it warm and it will seem gummy even when perfectly baked.

Kvass is one of the most resourceful ferments in the European tradition — a lightly fizzy, low-alcohol drink built from stale rye or sourdough bread. For centuries it was the thrifty answer to the question every sourdough baker eventually asks: what do I do with the heels and the loaves that went hard?

The bread is toasted dark, steeped in hot water, then the sweetened liquid is fermented for about a day with a pinch of yeast or a spoonful of active starter and bottled until fizzy. It usually lands around 0.5–1% alcohol. Kvass closes the loop on a sourdough kitchen: the same wild fermentation that raised the loaf can turn its leftovers back into something worth drinking.

The full recipe, with quantities, steeping and bottling times, is in how to make kvass.

Soda bread is the outlier in this trio. It’s not yeast-fermented — it rises chemically, when baking soda meets the acid in buttermilk and releases carbon dioxide in the oven. There’s no starter, no bulk fermentation, and no proofing. You mix it fast and bake it immediately, because the reaction starts the moment wet meets dry.

So why include it among fermented breads? Because its defining ingredient is a ferment. Buttermilk is cultured, soured dairy, and that lactic tang is exactly what both flavours the bread and powers the rise. Without a fermented acid, the soda has nothing to react with — soda bread borrows the product of fermentation rather than the process.

These breads look very different, but they all grow out of the same fermentation literacy. Rye uses the sour itself as structure. Kvass turns finished bread back into a living ferment. Soda bread leans on a cultured dairy product for both lift and tang. Together they show how flexible “fermented bread” really is.

If you want to keep exploring, the sourdough FAQ and glossary defines the terms you’ll meet, and the active starter guide keeps your culture strong enough for a rye bake.

Not every fermented bread is sourdough, and not every dark loaf is pumpernickel. Choose the technique for the grain and intended result. A dense sliceable rye bread should not be forced into a white-wheat open-crumb workflow, while a ciabatta should not be repeatedly tightened into a boule.