Large Cotton Muslin Bags
Product Review (submitted on July 30, 2013):
I really had high hopes this would work well making water kefir.. to not have to strain out the grains each time. Just transfer bag from batch to batch. Tried every way I could think of to keep bag submerged in water kefir, so mold wouldn't form on top of bag. Took way too much time trying (unsuccessfully) one thing, then another. Just went back to straining.
Note from CFH: We do not recommend using a bag to hold the kefir grains. To reduce the risk of mold, allow the grains to culture in the sugar water and use a strainer to remove them at the end of culturing. A plastic strainer is perfect for the job: http://www.culturesforhealth.com/plastic-nylon-strainer.html