Here's Why You Should Avoid Using Old Sourdough Discard In Your Baked Goods

Sourdough starters may be able to "start your sourdough," but that versatile brew can be used for a lot more than just bread. Some bakers add a portion of sourdough discard to their baked goods as a replacement for some of the flour and water. It makes a dimensional acidic ingredient, adding a pleasant, subtly tangy flavor to baked goods, not unlike stirring a few scoops of cream cheese into your dough or batter. But after about two weeks, sourdough discard is liable to hit your baked goods with an unpleasant, overly sour taste. "Sour" might be a good thing for kimchi, but not so much when it comes to sweet cakes and brownies.

When a sourdough starter is "fed," fresh flour and water are added into the container. To make space for this new addition, a portion of the existing mixture needs to be removed and "discarded." This thin, sour-smelling liquid is the discard, and it can either be tossed in the trash or repurposed as an ingredient for making other baked goods.

Discard can be stored in any airtight container in the fridge. That lower temperature puts the wild active yeast in the discard to sleep, effectively pausing the fermentation process. While discard will technically keep from going bad for up to several weeks in the fridge, after the two-week mark, it'll be too sour to be used in baked goods without seriously impacting the flavor. (And if you spot any of these sourdough starter red flags it's best to skip it altogether.)

The whole reason that discard exists (other than preventing your starter container from overflowing after every feed) is so that the live active microorganisms in the sourdough starter have plenty of fresh medium to eat and thrive in. Once the wild yeast and lactic acid-creating bacteria (the things that make your sourdough starter "alive") have converted all of the starches into simple sugars, that portion of the starter will no longer be able to rise and has become inactive. The unfed, ripe discard that gets scooped out represents inert media, increasingly deteriorating the longer it's separated from the mother culture. As a result, the newer the discard, the lower the acid.

For the lowest risk of messing with the flavor of your baked goods, stick to fresh discard, baking with it immediately after removing it from the starter. A slightly mature, week-old discard could also be a safe bet for working into more savory baked goods like pizza crust, biscuits, or quick breads, where a sour flavor won't negatively impact the overall taste. But always take care not to overdo it when incorporating this acidic ingredient into your batter or dough. As a general rule, sourdough discard shouldn't replace more than ⅓ of the flour called for in the recipe.