Master's Mix was chemically engineered for gourmet and medicinal mushrooms. Our proprietary blend contains a mix of saw dust and soy hulls. The hydration of every batch is PH tested and brought to field capacity. Each bag is weighed and sterilized, then cooled and sealed in front of our MERV-rated, HEPA filtered flow hood. Our substrate bags are available to be used immediately and are shelf-stable for up to 8 weeks from the batch date.