Like many culinary skills -- including canning, pickling, and breadbaking -- homemade yogurtmaking involves a lot of science, a good handle on technique, and a bit of art. It's not a tough skill to master, but if you run into trouble in your early efforts, please consult the list of potential issues below. In no time you'll be making delicious, creamy yogurt each and every time.
Question: Help! I followed your instructions and my yogurt never thickened! What did I do wrong?
Answer: A few factors can prevent yogurt from thickening (or "gelling") during fermentation. Did you:
- Use a thermometer? One of the easiest ways to kill off the live bacteria in your starter is to add it before your milk has fully cooled to 115°F. Experienced yogurtmakers know how to gauge this temperature by dipping a clean finger in the milk, but newcomers to yogurtmaking should definitely use a thermometer. And dip that thermometer all the way into your saucepan. (The milk at the bottom is often hotter than the milk on top.) If the thermometer reads higher than 115°F, wait until it reaches that temperature before adding your starter.
- Keep your yogurt pot warm? Thermophilic yogurt cultures (those most commonly used in commercial yogurts) thrive only in warm environments. This is why it's so crucial to keep your yogurt pot warm (between 100°F and 110°F, though I prefer a stable 110°F) throughout the 6 to 12 hour incubation. If your pot cools too much, your starter bacteria can't do their job and you'll be left with the same warm milk you started with. Consult the Official Yogurt Culture Master Homemade Yogurt Recipe for our favorite three ways to maintain warmth. If you're getting creative (using a slow cooker, using glass jars in a warm water-filled cooler), you'll also be able to achieve good results so long as you can ensure that the milk stays within that target temperature range.
- Use fresh starter? Yogurt bacteria are alive, but they can also lose their effectiveness over time or simply die. If using commercial yogurt as your starter (we'll cover heirloom, freeze-dried, and mesophilic starters in a future discussion), make sure it is relatively freshly opened (flexible, but within a few days or so) and well before its expiration date. The label should clearly indicate that the cultures are "live" and "active." Happy, living bacteria are essential to creating beautiful yogurt.
- Use milk with some fat? While it is certainly possible to make yogurt from fat-free or 1% milk, you will not get the same creaminess and thickness. Some people "mount" their fat-free milk with thickeners and milk powders, but we prefer to use whole milk instead.
Question: My yogurt is lumpy! Did I do something wrong?
Answer: Maybe, but maybe not.
- Did you follow all the time and temperature protocols precisely and use fresh starter? If so, you may have perfect homemade yogurt but just not be accustomed to what natural, from-scratch yogurt looks like. A bit of lumpiness is to be expected and very easy to "fix" if the lumps bother you. First, chill your yogurt for at least 6 hours. Next, strain out some of the whey for a few hours (you can do this in the refrigerator). Finally, gently whisk the yogurt, adding a small ice cube as you whisk to remove any remaining lumps. Voila!
- If, however, you kept the yogurt pot at too high a temperature during incubation, this can result in yogurt with a variety of unpleasant, off-textures (you'll know them if you encounter them). Next time, try to keep the pot warm but never hot during your 6 to 12 hour incubation.
More questions? Yogurt Culture has a 4-page troubleshooting section in the back of the cookbook.
Feel free to pose additional questions in the comments. We'll be adding to this document over time and are here to help you troubleshoot. Always keep in mind that yogurtmaking is an ancient culinary tradition that people in a huge number of countries in varied climates (and with very limited equipment) have done successfully. We know you can do it, too!