After the yogurt has been in the fridge for several hours, take a taste. If a thicker yogurt is desired, drain it. Draining yogurt dramatically improves its texture, making it thicker, creamier, and more mellow by removing the whey. Draining yogurt also extends its life. And if you are lactose-sensitive, you should find drained yogurt more digestible.
To drain your yogurt, gently pour the chilled yogurt into a colander or strainer lined with three layers of dampened cheesecloth. Cover with a plate or cloth—you’re protecting the yogurt, not pressing it—and place it in the fridge. Drain the yogurt until it has the consistency you like. After an hour, the yogurt will be noticeably thicker. If you drain the yogurt more than you’d intended, no problem, simply whisk some of the whey back into the yogurt, adding as much as it takes to attain the textures you desire. Scrape the drained yogurt into a container, cover, and refrigerate.
To make Greek yogurt, which is essentially drained yogurt, instead of stopping after an hour of draining, keep going. Depending on the yogurt you started with, it may take 3 to 4 hours to achieve the thick, palate-coating consistency of Greek yogurt.
Don’t be concerned if each batch of yogurt you make is a little different. Unlike commercial producers with their controlled processes, your home yogurt “factory” is subject to variability: in the milk and culture used, the way you heated and cooled the milk, the length of the fermentation, and the fermentation temperature. Experiment, make notes, and over time you will find the combination of culture, time, and temperature that produces yogurt with the texture and flavor you like.