Class Time: Sourdough Discard 101

Just about everyone knows what sourdough discard is, but in case it’s new to you: Sourdough discard is what’s left behind after you refresh your starter. Or if you are paranoid like me, it’s what your backup sourdough culture becomes once you’ve refreshed your starter and the leftover becomes the new backup. (I’ve said this before, but I keep three 1-quart containers in my fridge: recently-refreshed starter for baking, the previous starter as a backup in case of disaster, and a third container with all the combined previous backups. The last one is my sourdough discard.)

Why use discard?

We save sourdough discard because we are frugal and tossing it feels wasteful. And because it’s actually quite useful, even though it lacks the structure and leavening potential of fresh levain. (By the time starter becomes discard, both the gluten and the yeast and bacteria it contains have degraded.) But it’s still fermented, and sourdough-fermented flour is good for you, or at least not as bad for you.

Sourdough discard—and long-fermented sourdough products in general—are generally considered more nutritious than either unfermented or yeast-fermented flour-based foods. The acidity of sourdough degrades phytic acid, a common chemical component in seeds, including wheat. Phytic acid binds tightly to important minerals, making them less bioavailable; degrading phytic acid thus releases minerals to make them easily absorbed by the gut. There’s also evidence that lactic acid/sourdough fermentation can increase the concentration of some antioxidants and vitamins in the food.

Sourdough products are also more easily digested than unfermented or yeast-fermented, flour-based foods, for a couple of reasons. One, it’s known that sourdough fermentation can generate prebiotic compounds, a fancy term for chemicals that help sustain beneficial gut bacteria. Two, sourdough fermentation degrades gluten, which can make it more tolerated by celiac or gluten-intolerant people. (I’ve heard from a fair number of people who avoid flour unless it’s been fermented with sourdough for precisely this reason.)

Discard recipes

I have a few thoughts about for makes for a good sourdough discard recipe.

First off, I tend to avoid recipes that include sourdough discard and then ferment the dough, particularly with the intent of gaining volume in the final product. While that sort of approach can work, it depends entirely on the age/health of the discard. I’d rather use fresh levain in those cases, so I can easily judge how quickly it will ferment. So I don’t really do sourdough discard breads.

Secondly, I’m not that interested in recipes that use a tiny amount of discard relative to the total amount of flour, for two reasons. One: If only a fraction of the flour in the recipe comes from the discard, it’s not really doing much either in terms of flavor or increased digestibility/nutrition. And two: Discard is something that tends to accumulate in the fridge—I want to use it up, so the more a recipe uses, the better. The ideal discard recipe is one that gets 100% of its flour from the discard, though that’s a lot to ask, since you often need to give it more structure—or dry it out—with fresh flour. Fifty percent of the total is the minimum I aim to use.

Recipes are typically created by taking a recipe for some flour- and liquid-containing recipe and substituting sourdough discard for some or all of the flour and liquid in the formula. They typically fall into four categories:

Where the discard replaces flour and water. These are the easiest to devise, and often the most successful, since it’s usually a simple, even swap.

Examples include: pie crusts, puff pastry, water-based pastas, noodles, crackers, and unleavened flatbreads like tortillas.

Where the discard replaces flour and an acidic liquid ingredient such as buttermilk or milk (milk is slightly acidic). This is where the use of sourdough discard makes the most sense: It has much the same viscosity and pH as buttermilk, and usually works quite well as an even swap (think sourdough pancakes vs. buttermilk pancakes). The one problem with replacing a dairy product with discard is that the latter lacks milk proteins, which are useful for flavor and increased browning. For this reason, I often add dehydrated milk powder to the formula (9% relative to the total weight of water in the recipe).

Examples include: pancakes, biscuits, scones, crumpets, some muffins, cakes, and quick breads.

Where the discard replaces flour and eggs. Recipes that get most or all of the water they contain from eggs are challenging to adapt to discard without altering the results for the worse. That’s because sourdough discard doesn’t have the structure-providing proteins of egg whites and yolks, nor the richness-providing fats from yolks. Usually you need to retain some if not all of the egg product in the formula, which means adding more water overall. Sometimes a longer bake is enough to drive off the excess moisture, but there are many instances where the additional water causes the texture of the product to suffer (cookies can get tough, for example).

Examples include: Egg-based pastas, many muffins, cakes, quick breads, and cookies.

Where the discard replaces flour and butter. Recipes that get most of what little liquid they contain from butter are the hardest to convert to discard without disastrous results. Take shortbread cookies, for example: they are “short” and crumbly precisely because most of the flour they contain never comes into contact with water. Water + flour = gluten development, which is anathema to a short baked good. Keeping the cookie tender generally requires coating the remaining flour well with butter before adding the starter, and limiting the amount used.

Examples include: Short cookies and pie crusts.

I’ll have versions of each of these recipes here eventually. Please share your thoughts on sourdough discard recipes below, including any requests for specific recipes!