Disclosed is a formulation for preserving the life of probiotic bacteria during passage through the stomach, while permitting their release in the intestine, and which has a low water activity and correspondingly long shelf life. These formulations are designed to retain potency up to the product expiration date. The formulation includes a substantially water-free mixture of probiotic bacteria with monovalent alginate salts, wherein the mixture has been formed and is maintained in a substantially water-free environment. The alginate salts include sodium alginate and potassium alginate, but not divalent salts such as magnesium alginate or calcium alginate. Generally, an enteric coating (e.g., gelatin or cellulose encapsulation) for the formulation is provided.