In order to keep a sourdough starter (“yeast baby”) viable for baking purposes, it is necessary to feed it regularly. The more consistent you are with the feeding schedule, the more reliable your starter will be for baking delicious breads (and other things, too).
-Jar of sourdough starter
-Clean spare jar
-Kitchen scale that weighs grams
-Bag of unbleached white flour
-Container of filtered water
The golden rule is a 1:1:1 ratio — to take one part by weight of the existing sourdough starter and add to it one part flour and one part water. Mix that all together into a clean jar until there are no dry lumps of flour. I like to use a regular table knife to mix with since it’s easy to scrape off.
If you are not going to be baking in the near future, use a minimal weight, like 15g of each the existing starter, flour, and water. Keep that jar in the refrigerator for up to a week before you feed it again. You can use the leftover starter to make pancakes, start a backup batch, or just throw it out.
If you are going to be baking, you will need to figure out how much starter the recipe calls for and divide that by 3, with some left over for continuing the starter. For example if we wanted to make my standard sourdough loaf, it calls for 120g of starter, which requires 40g starter from the jar, 40g flour, and 40g of water (40+40+40=120). But we’d also want about 15g extra starter to keep the starter going in the jar. Weigh out whatever you have left from the jar of starter, whether it is 15g or less, and add equal parts flour and water to it. Be aware that if you end up with less than 5g of your starter to continue on with, you may fundamentally change the character of it going forward.
After feeding, let the yeast baby sit for two to five hours until it has doubled. It is called “fed” starter after it has roughly doubled. This is when you should put it to use.
Things can go wrong. I tend to keep at least one backup jar of starter in the fridge in case I break the jar, or somebody mistakenly throws it out, or I feed it almond flour because I’m too tired to realize what container is in my hand.
If your sourdough starter starts developing odd colored blotches, it could be mold. If this is your only starter and it is mature (usable for baking), take a portion of an unaffected area and start again with that. It may have been caused by contamination or too warm an environment. It could also be weird blotches from using a flour that isn’t entirely pure, like a malted flour or enriched flour. If that’s the case, just switch to using just 100% pure unbleached white flour.
If your yeast baby develops a layer of liquid along the top, it is alcohol and you are starving it of precious nutrients. Pour off the alcohol and give it more consistent feedings. It should recover, but it may taste different.
Temperature will impact the kind of yeast that dominates. You may find that you prefer the flavor or behavior of a sourdough starter that’s kept mostly in the fridge versus one kept mostly at room temperature, or vice versa. You also can slightly vary the amount of water away from a 1:1:1 ratio to favor different types of yeast. Knowing the specific impacts on types of yeast is beyond my expertise, so I would encourage you to turn to your own research if you’d like to know more about that.