Quick Answer
To use a thermos for yogurt culturing, you'll need to create a warm, stable environment for the bacteria to grow, typically between 100°F to 110°F (38°C to 43°C). Preheat the thermos with hot water, then add your yogurt starter and milk mixture. Keep the thermos in a warm, draft-free area.
Preparing the Thermos and Ingredients
To start, preheat your thermos with hot water (around 180°F or 82°C) for about 10-15 minutes. While the thermos is heating up, prepare your ingredients: 1 quart (960 ml) of milk (whole, low-fat or nonfat) and 1/4 cup (60 g) of plain yogurt with live cultures. Once the thermos is preheated, discard the hot water and dry the interior with a clean towel.
Assembling and Incubating the Yogurt
Add the milk to the preheated thermos, followed by the yogurt starter. Stir gently to combine and distribute the starter evenly. Seal the thermos lid tightly to prevent contamination and ensure the warm environment. Place the thermos in a warm, draft-free spot, such as an oven with the light on or near a fireplace, maintaining a consistent temperature of 100°F to 110°F (38°C to 43°C) for 6-8 hours.
Monitoring and Storing the Cultured Yogurt
After 6-8 hours, remove the thermos from the incubation area and refrigerate the yogurt to slow down bacterial growth and allow it to set. Once chilled, the yogurt should be thickened and have a slightly tangy flavor. Transfer the yogurt to an airtight container and store it in the refrigerator for up to 1 week.
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