If your milk kefir is not thickening, there could be a few reasons. First, your grains may not be working properly. If they are brand new grains, you may need to do a few batches before they start working. Use less milk while activating so that you have less waste. If your grains were working fine before, then maybe you left them too long without straining, it can cause the grains to be stressed out. Rest your milk kefir grains in fresh yogurt with live active cultures for a day to help them rebalance, then try again with a smaller amount of milk. Your kefir grains can die if they are left too long without fresh milk. So if you try this and it does not help, you may need to get new grains. It's a good idea to freeze a tbsp or so of your grains when they grow so you have back-up. Another reason for thin kefir is moving the jar around too much while fermenting. I've found it best to just set up the jar and leave it until I can visually see that the milk has thickened. Then I'll strain and refrigerate the kefir right away. Also keep in mind that some milks are much thinner than others. You can add cream if you are not using milk with high fat content (such as that from Jersey and Guernsey cows). Goat milk tends not to thicken much, but you should notice it has developed curds instead of being smooth milk.