Pourable Plain Skim Milk Yogurt

Steps

1. Wash a heavy pot, a whisk, a ladle, a small bowl, a clean quart jar with lid and a thermometer in hot soapy water, rinse, then sanitize them with boiling water and let them air-dry.
2. Set the Greek yogurt out on the counter to take the chill off while the milk heats; it will be used as the starter in step 5.
3. Pour the commercially pasteurized skim milk into the pot and heat over medium-low, stirring often, until it reaches 180°F (82°C). Hold it at 180–185°F (82–85°C) for 10 minutes, stirring; a shorter hold keeps this yogurt thin and pourable.
4. Take the pot off the heat and cool the milk to 108–112°F (42–44°C), about 30–40 minutes, or faster with the pot set in a sink of cold water, stirring now and then.
5. Ladle about half a cup of the warm milk into the small bowl, whisk in the Greek yogurt until smooth, then whisk this starter mixture back into the pot of milk.
6. Pour the cultured milk into the sanitized jar, cover, and incubate at 108–112°F (42–44°C) for 6 hours in an oven with only the light on or a warm cooler, checking with the thermometer, until just set and gently wobbly.
7. Refrigerate the jar immediately at 40°F (4°C) or below and chill for at least 4 hours.
8. Whisk the chilled yogurt briskly until smooth and pourable; do not strain it, so the yield is about 1,000 g (about 4 cups), roughly 1 cup per serving. Keep refrigerated and use within 1 week.