Short answer: Mine were okay after about 5 months or so. Long answer: I stopped making kefir for about 5 months from October 2013 to March 2014. The whole time the kefir grains were just sitting in a corner of the fridge with about 200ml of milk. About a week ago, I decided it was time to start making kefir again. When I took out the 5 month old kefir, it smelled really sour with a tinge of alcohol* and was a lot thicker than normal. There was a layer of yellow crust on top of it too.
I strained the kefir and noticed the remaining grains had smaller clumps than they usually had but were otherwise okay. I rinsed the grains with milk and then put them into a fresh container of UHT milk since they were the only thing I had around at that time. The next day, the kefir was ready. It looked fine but smelled a bit off, kind of like sulphur or rotten eggs but that’s okay because it was exactly what I got when I made kefir for the very first time with grains that came in the mail. I threw out the kefir though and put the grains in new milk again. Another day passed and this time, the kefir returned to normal. I was able to make a smoothie with it and it tasted fine 🙂 Previously, I thought you had to store the kefir grains in the freezer if you wanted to stop making kefir for a while. However, I didn’t do that this time (I forgot I had them in the fridge) and the grains were still viable even after 5 months. I’m not saying that it would work for everyone but if you left your grains in the fridge for a long time and aren’t sure if they’ll still work, it wouldn’t hurt to try. If you need to buy new grains though, this post might help. *kefir contains a very small percentage of alcohol but it isn’t usually noticeable if you don’t leave it as long as I did.
What about frozen grains?
I read an e-mail dated 27 May 2014 from a kefir making yahoo group, posted by Shirley from West Virginia. Apparently, her frozen grains were successfully reactivated after a period of more than 13 years! This was what she said (my emphasis in bold):
Dear Readers, I am a new, (well, 76 years old!) member of this group. I joined specifically to tell you about my ancient kefir grains. In 1999, my daughter, who was really, really into health foods, sent me some kefir grains that she said she had gotten from Australia. Well, I tried them out but eventually got bored with it and froze them. I put them in a small plastic container covered with powdered milk and labeled the container: 2/22/01. Yes, 2001. Two days ago, I thought about them while investigating Paleo diets and pulled them out. I rinsed them off using bottled water. Didn’t look like I had many grains! But, I put them in a glass quart canning jar (plastic lid), added some warmed (to baby bottle wrist temperature) whole fat grocery store milk and put the lid on loosely. Twenty-four hours later, I had larger grains, but watery milk. Poured that off and added some more warm milk (about a cup). Today, I got up to some fantastic kefir….smelled right, was thick, no watery layer. The grains are now about the size of the end of my thumb. So, I poured that off and added some more warm milk and this evening it is thickened up and ready to go again!!!! This experience belies everything I have read about reconstituting kefir grains. I use a plastic canvas round (cut to fit) in the metal ring that fits the wide-mouth canning jar. The kefir does not touch the metal because of the plastic ring insert. It drains off nicely and I can use a plastic or wooden spatula to put the grains in a clean jar and add more warmed milk. I do not know if you all are really interested in this but I though you might be interested in knowing that frozen kefir milk grains can last a very, very long time. Jurassic Park may not be just an unbelievable movie!!!! Shirley in WV