Here is a website that my sister-in-law Autumn directed me to with more information on the kefiring process (click here to read our previous discussion about this). I found out some interesting information about caring for and storing your grains. The following says that grains don’t need to be rinsed between uses after all:
As long as utensils are kept clean and ingredients are fresh and of the highest quality, rinsing kefir grains is not necessary. Rinsing kefir grains came about after the mother-culture including kefir were introduced to the rest of the world. It came about in recent years, possibly due to concerns regarding weed microorganisms settling on the grains. The robust nature and properties of the microflora, and possibly the physics behind the grains themselves, are effective inhibitors or can antagonize the growth of weed organisms. I am able to exploit this very nature of kefir, by implementing kefir as a natural preservative for preserving fresh foods in solutions containing as little as 10% kefir or kefir-whey, with exceptionally good results.