You can test the temperature by touch: the milk should feel comfortably warm, allowing you to keep your finger in it for about five seconds without discomfort. However, using a thermometer is the most reliable way to check the temperature.

If you’re in a hurry, fill a large bowl with ice water and place the pot of milk in the ice bath. Stir frequently until the milk cools to 115°F (46°C).

Transfer ½ cup of the warm milk to a small bowl and whisk in the yogurt starter until smooth. Pour the mixture back into the pot of warm milk and whisk thoroughly to ensure the starter is evenly distributed.

Cover the pot and place it in a warm spot. Wrap it in a thick blanket to help maintain a consistent temperature. Avoid moving or stirring the yogurt while it ferments. Let it sit for 6–12 hours, or until it has thickened and developed a pleasantly tangy flavor. The longer it ferments, the tangier it will become.

Once the yogurt has set, refrigerate it. Homemade yogurt can generally be stored in the refrigerator for about 1–2 weeks, provided it is handled hygienically and kept consistently cold.