Why You Should Never, Ever Put Sourdough Starter Down the Sink

If you just made a beautiful loaf of sourdough bread and aren’t sure about how to dispose of leftover starer, definitely don’t pour it down the sink drain. Compost it or dump it in the trash in a sealed bag, but never put the starter—or sourdough dough for that matter—down the drain. While it might seem like the flour and water would simply dissolve under running water, a plumbing expert says that’s not the case.

“Pouring sourdough starter down the sink drain won’t cause an immediate issue but is likely to lay the foundation for a clog in your pipes,” says Danny Pen, president of New Era Plumbing & HVAC. The sticky starter clings to the insides of the pipes, trapping other debris and slowly drying out, only to result in blocked water flow and a clog that’s a job for a professional. Pen adds that you should avoid pouring any flour-based, doughy, or starchy product down the sink drain—that includes things like pancake batter, bread dough, pasta dough, and even mashed potatoes, as they all cause the same clogging problem. Read on for more details, as well as a tips what to do instead.

Why You Shouldn’t Pour Sourdough Starter Down the Sink Drain

“Dry or wet, a lot or a little—sourdough starter should never go down the drain,” Pen says. He compares it to wet cement, explaining that it can stick to the walls of the pipes and traps other debris. The starter hardens over time, which leads to hard-to-remove blockages in the pipes and a reduced pipe diameter. Pen says drain pipes and the P-trap are especially vulnerable and the spots where sourdough starter settles.

If you’re wondering whether it’s safe to pour dry sourdough starter down the drain, the expert has a clear answer: no. “Dry sourdough starter isn’t safe either, as it turns into the same sticky, glue-like mess once it’s exposed to water,” he says.

How Sourdough Starter Affects Your Plumbing

Whether it’s sourdough starter or another wet batter, the sticky mixture of flour and water doesn’t just wash away as you may expect it to. “It clings to the walls of your pipes and, like a snowball, picks up other debris like grease, coffee grounds, soap scum, food scraps, and hair,” Pen says. What you’re left with is a mass of sticky gunk which slowly thickens and then dries out, creating what the expert says is a rock-solid clog. This results in significantly reduced pipe diameter and potentially completely blocked water flow.

Removing a clog of this kind is a complex task even for a professional according to Pen and he equates the task to trying to scrub dried dough off a countertop or bowl. “Getting it out of your pipes is something similar but even more problematic and requires a professional to address it,” he says.

How to Safely Dispose of Sourdough Starter

To safely dispose of sourdough starter, Pen says you have two options: throw it in the trash or compost it. If you’re going to dump it in your trash can, make sure you place it in a sealed bag or an airtight container first in order to avoid an unpleasant sour smell from taking over your kitchen. If you have access to a compost bin, you can choose to compost sourdough starter. It’s an organic substance so it’s compost-friendly, and this disposal method offers an environmentally-friendly solution that won’t mess with your plumbing.

Other Ways to Use Leftover Sourdough Starter

If you have leftover sourdough starter and aren’t sure what to do with it, instead of pitching it, turn it into something delicious instead. “Pouring sourdough starter or dough down the sink isn’t just bad for your plumbing—it’s also a waste of good food,” says Valerie Agyeman, registered dietitian nutritionist and host of women’s health podcast, Flourish Heights. She suggests saving the extra starter for future baking or getting creative and using it in other recipes. “If you’re into food waste reduction, you can repurpose sourdough starter in things like pancakes and waffles for extra fluffiness or even crackers for a delish homemade snack,” Agyeman says.