1 quart whole milk
1 heirloom yogurt starter culture or 1⁄4 cup of plain yogurt or kefir
Heat milk very slowly in a saucepan to 160°F. This alters the milk's whey proteins and helps create a firmer, denser consistency. The longer you hold the milk at this temperature, the thicker your yogurt will be.
Let the milk cool to 110°F. Add the starter culture and mix well. Keep it warm at 110° in a yogurt maker or try one of our Fermentation Incubation Hacks to maintain the temperature until the yogurt has the consistency of thick cream. This usually takes 6-8 hours, but may take up to 12. Stir the yogurt, then refrigerate. Homemade yogurt should keep for 2-3 weeks in the fridge.
Save 1⁄4 cup of finished yogurt for your next batch. If you used an heirloom yogurt starter, you can save 1/4 cup of reserved yogurt to culture your next batch indefinitely! If you're using store-bought yogurt, you usually can only re-culture 2-3 times. After a few batches, yogurt will not set well and the tart flavor will wane.