Portable reusable fermenter for easy preparation of homemade kefir with use of kefir grains restrained in the plastic chamber submerged in the milk. Chamber has large number of halls for easy access of milk to kefir grains. The size of halls is significantly smaller that the size of kefir grains in order to keep grains inside chamber but big enough for free access to milk. Portable fermenter with the same set of grains is reusable. Drinking of kefir can be done through plastic straw without of separation of grains and ready kefir.