Milk kefir is an incredible probiotic, natural product. We always have kefir in our fridge and drink on a daily basis. If you are about to go on holidays and must find a way to keep your babies alive, fear not! The kefir grains are very easy going little animals (bacteria and yeast symbiotic colonies in reality), which can be preserved and stored in two different ways, depending on how many days you will be away from home. It is also very reasonable to have a backup of grains, in case an unexpected disaster happens, which is not very uncommon in DIY / home made products. Whatever the reason you want to store/preserve them, here are the 2 options I highly recommend.
Keep them in the fridge, inside a closed glass jar with some milk. In this way, the fermentation process is slowed down remarkably and the grains are more or less in hibernating mode. They can last in the fridge for a few weeks. I have personally tried this option and found that even after 6 weeks, the grains were good to go. When you are ready to use them again, you simply take them out of the fridge, put them in fresh milk and leave them to re-adjust to the new temperature. The first couple of fermentations after refrigeration will take a couple more days than normal but this is to be expected as it is a significant transition for the grains.
For me this is the most practical solution because it does not require any kind of energy source or machine. Milk kefir grains are the easiest to dry and store. When you dry the kefir grains you want to kep them on a thick cotton material for about 2 weeks, but dont expose them directly to the sun. I use jeans fabric cut from old pants, which is thick, absorbing and durable. In order to avoid them getting dirty with dust or other flying dirt, keep them covered with the same fabric or with a piece of kitchen paper. As the grains get drier and drier, the will shrink and turn yellow. This is normal. You can keep the grains like that for a very long time. I have tested them after 2 months of being dry and they work perfectly. Like the other option, it might take a couple more days than normal for the first couple of fermentation to finish (this will also depend on the room temperatture that you keep the kefir in), but after that, everything will be as normal. Once they are dry, you can keep them in a closed glass jar, away from direct sunlight. The process of drying milk kefir grains is shown in the picture below.