While we recommend using your mushroom plug spawn as soon as possible while they are at their prime, they can easily survive for months refrigerated in a cold dark place. (In fact fungal mycelium is amazingly resilient, and cultures are often still viable even after a year or more!) A small amount of yellow or amber liquid may collect in the bottom of your bag over time. Not to worry, the liquid is naturally-forming metabolites, a by-product of mycelium growth. It is still perfectly good to use.