Tibicos, also known as tibi, water kefir grains, sugar kefir grains, Japanese water crystals and California Bees, are a culture of bacteria and yeast held in a polysaccharide matrix created by the bacteria. As with kefir grains, the microbes present in tibicos act in symbiosis to maintain a stable culture. Tibicos can do this in many different sugary liquids, feeding off the sugar to produce lactic acid, alcohol (ethanol), and carbon dioxide gas which carbonate the drink (i.e. makes it bubbly).

Tibicos are found around the world, with no two cultures being exactly the same. Typical tibicos have a mix of Lactobacillus, Streptococcus, Pediococcus and Leuconostoc bacteria with yeasts from Saccharomyces, Candida, Kloeckera and possibly others. Lactobacillus brevis has been identified as the species responsible for the production of the polysaccharide (dextran) that forms the grains.

People who do not wish to consume dairy or have a Vegan type diet may find that water kefir provides the living pro-biotics without the need for dairy or tea cultured products, like kombucha. Since the finished product, if bottled, will produce a carbonated beverage, it provides an alternative to sweet soda drinks for children and adults.