White Labs Liquid Brewers Yeast is tested to be over 95% viable, 100% free of wild yeast, aerobic bacteria and anaerobic bacteria. Each vial contains a "pint starter" of yeast and is designed to be added directly to 5 gallons of wort or must. The shelf life of the White Labs Liquid Yeast is a minimum of four months from the "Best Before" date on the vial, and if refrigerated will stay alive for over a year. Best results are found if used within the "Best Before" date.