Our standard Wyeast product is the now the 125 ml Wyeast XL Activator pack. When prepared by smacking the package 3 or more hours prior to brewing, Wyeast's Acivator packs yield an average of 100 billion yeast cells. This is the most yeast of any "pitchable" yeast product sold for home brewers. And, unlike yeast sold in tubes, Wyeast's famous "smack pack" means that you can be 100% certain of yeast viability before putting it in your beer—a very important consideration when buying yeast by mail. Wyeast is packaged in a sterile "smack pack." Activate at least 3 hours before brewing by smacking the inner nutrient pouch and mixing with the yeast in the outer pouch.