Mushroom fungus is susceptible to other fungi outcompeting it
in the air around you has millions/billions of spores of other fungi and other things.
when you make a nice nutrient-filled media/grains/Substrate if any of those other fungi spores land in your work they will grow like wildfire and outcompete your mushroom fungus
a flow hood filters all the spores and particles in the air so when you open your work in the sterile airstream there’s nothing in the airflow to land in your work and start growing
this allows you to drop only your clean mushroom fungus into your work and seal it
something to keep in mind
– your hands and arms need to be clean while working, as things can land on you and blow off into your work while you work
Another option if you don’t have the funds for a flow hood, make a “still airbox” its a great place to start
but a common thing always said to us by customers (I don’t know how I ever lived without a flow hood)