Time and temperature are the two most important factors that affect how your kefir will look and taste. During the summer months, kefir may be ready to drink in 17 to 18 hours. If you let your kefir sit too long at summer temperatures, it will first become thick and eventually start turning into cheese and whey. If your kefir is “lumpy” and too sour, you are definitely leaving it out too long. It should be creamy, slightly thickened and “drinkable”…a little thicker than milk. Taste your kefir to know when it is ready and don’t let it get too tart. When it is just right, shake it well and place it into your refrigerator. Kefir will often thicken a little more in the fridge, since it is continuing to culture, but at a much slower pace. During the colder months of winter, your home will likely be 10 or more degrees cooler. It will take more time for your kefir to culture at these temperatures. Since people live all over the United States and the weather varies so much depending on location, you will need to check each batch until you know what is the best for you. With each batch you make, adjust the time until you get it just the way you like it.
When you make a transfer of a small amount of kefir into fresh milk or fresh juice, the strength of the culture and the amount of kefir you transfer will affect how quickly the new batch is ready. If you transfer too much kefir your product may culture too fast and become too sour for you, so be careful.