I was recently asked about how to care for a sourdough starter and thought I’d write down what I’ve learned over the years. The very short version is, “If it doesn’t look active, I should feed it.” The longer version is below. I hope it’s helpful.

Sourdough starter is a concentrated collection of wild yeast and bacteria that produce water, ethanol, CO2, acetic acid, and lactic acid along with countless other compounds bakers are less interested in. Simply by providing food for them, these microbes will reproduce in enough quantity to be useful baking bread or other products.

When I look at my starter, I generally think of it in one of three states: active, sleepy, or dead. Active starter will bubble and grow in size within a few hours (1-4ish) of feeding. Sleepy starter happens for a number of reasons we’ll explore below but is generally characterized by slowly bubbling and only showing sign of an increase in volume after 8 or more hours. Finally is dead starter. This shows no signs of activity after a day or more. But, here’s the good news, with all the wild yeast and bacteria in your kitchen, if you keep feeding a starter (even a dead starter), it will be active within a week.

Feeding and care of your starter is something a lot of people fret over. So first thing, relax and don’t overthink it. Remember, the worst thing that could happen is you kill your starter in which case, you feed it for a week and you’re back to an active starter. Next, there are a lot of methods for feeding and care. I’ll explain what works for me, but if it doesn’t work for you, think about the important points listed below and try any method that covers those points and works for your schedule. I typically bake a sourdough loaf every 3 days so I keep my starter active and on the counter. I pull off 100g to start my levain, leaving about 30g in the jar. I add another 50g room temperature tap water and 50g flour (usually bread flour, sometime whole wheat) to the jar with the remaining starter, mix well, cover and ignore until I need it again in three days.

Important points for feeding:

• Discard: If you’re not using your starter, it’s very tempting to just keep feeding it rather than discarding the majority of the starter. Don’t do this. I did it; it’s doesn’t work. Over time, your starter builds up too much ethanol and acid and all the microbes stop working. If you really don’t want to waste 100g of starter, save it in the fridge or freezer and throw it in your next bake to add a little funkiness, but don’t expect it to contribute much to the rise. At least once a week (if it’s on the counter) or once a month (if stored in the fridge), discard most of the starter and feed it at least double the mass you are keeping (as above, keep 30g and feed it at least 60g, I do 100g)
• Counter vs Fridge: If you plan to use your starter again within a week, I would keep it on the counter. If it is going to be longer than a week, put it in the fridge after feeding to slow down their eating and conserve food/flour. If you put it in the fridge, your starter will be “sleepy” when you pull it out so know that it will take a day or two before it is active again. I wouldn’t recommend putting it in the freezer.
• Feeding ratio: I like to use equal weights of flour and water. If you use more water, the starter will be active faster and go through the food faster. If you’re baking daily, maybe go with more water. If you’re baking once a week or less, maybe go with less water. I’ve never worried too much about this and equal weights is simple for me to remember.

What could possibly go wrong??? If you feed your starter and it isn’t active within 8 hours, what should you do? Feed it again. There are a lot of problems that can happen with starter and most of them are solved by more feedings/discardings. As I mentioned above, if you keep feeding your starter without using or discarding any, the ethanol produced by the yeast as well as the lactic and acetic acids will build up to the point that even the microbes we want are having a hard time surviving. By discarding some and feeding, you bring the pH closer to neutral and remove ethanol. Another problem is that the starter went through all of the food, so you’ll want to feed it.

Temperature can also greatly impact your starter. The microbes in the starter are most active around 90°F. If you go much hotter than this, they will start to die off. We generally want to keep the starter cooler than this because the starter produces better flavor closer to room temperature. If we just think about three main products from starter fermentation (ethanol, lactic acid, and acetic acid), we get more ethanol and lactic acid at higher temperatures with more acetic acid at lower temperatures. Generally we want more balance in the bread with some of all of these flavors. If your starter smells like vinegar (acetic acid), you might want to store it in a warmer place or add slightly warmer water when feeding. If it smells boozy (ethanol) or slightly of yogurt (lactic acid), you might want to try to keep it a bit cooler. My starter sits on the counter which means I get slightly different flavor breads in the summer versus the winter due to changes in “room temperature”.

Once you’ve got the starter going strong and keep feeding it, everything should take care of itself, but sometime you need to leave it for an extended period and a few things can happen. The obvious thing is that your starter will be very sleepy so you’ll want to feed it. If the starter has been left in the fridge for a couple weeks, you might find a dark liquid floating on top. Don’t worry about it, it’s mostly ethanol. You can stir it back in, but I would just dump the liquid and feed the remaining starter as usual. Finally, if it gets fuzzy, this is unwanted and potentially dangerous mold. The best thing to do is get rid of the starter and begin a new one.

There’s plenty more to learn about starter, if you’re interested, but for most home bakers, any additional knowledge is to satisfy your curiosity. Know much beyond, “If it doesn’t look active, I should feed it” isn’t really needed to bake great bread. That said, this article gets pretty geeky pretty fast. Also, the above graphic provides some interesting information. Remember to relax because the starter will naturally survive with very little input from you… but also know, sometime a starter dies. It’s not a big deal, just leave some flour and water on the counter, feed it daily, and within a week you’ll have starter again. Finally, don’t cherish your starter too much. Even if the starter has “been in the family for 400 years”, after a month in your kitchen, the microbes in the starter are no different from a wild starter you caught in your kitchen. The local microbes will out compete the others so a starter that’s two weeks old is just as good as one that you’ve had for decades.

Have fun with it and happy baking