Old Kefir Grains will not work any more producing healthy probiotic bacteria in milk. They will be on the way of healthy grains doing no work. Besides that, they will be decomposing making the milk go off adding off taste to the Kefir.
The grains that get old and become dead (or are dying) become flat, white (vs creamy colour healthy young grains), hard (vs soft young healthy grains) and stretchy.
In general, when Kefir grains get sick (and it can happen due to a number of reasons), they get stretchy and "snobby". The grains can get sick from being placed in the fridge for too long or at too cold temperature. If you pour too cold milk on them straight from the fridge every time you ferment Kefir, it will cause them go sick over the time.
They also can get sick from being exposed to too hot temperatures. The ideal temperature is room temperature 10-25 C.
They will also get sick if you don't replace milk and let them sit in soured milk for too long, or if it happens too often. Leaving them for 2-3 weeks in LOTS of milk while on vacations once ot twice a year won't do them harm, even if they sit in soured milk for some time.
Sick grains get old and die quickly. To preserve the culture over a long period of time, you need to make sure you look after it well.
Regardless of general opinion that the grains need to be well rinsed after each fermentation, it will not do them harm. Rinsing under chlorine water or under too cold or hot water will do them more harm than just straining Kefir and transferring them to a new bowl/jar of fresh milk. Remember, that milk is their medium. They don't like to be exposed to water too much.
Good luck with your culture!
Any questions, please, ask in the form below.
Sincerely,
Tatiana
