"Phil..if you create a vacuum then the mositure from the product will boil off...hence my original question. What keeps the moisture in the product? "
I am still at a loss as to the question. I don't know enough about these to answer it, but maybe if you explain " boil off ', I can.
The moisture in the product you put in the vacbag is still there, that is, the pump does not suck the product dry. It really only sucks out the air.
I have bought.... say bacon from a supermarket that has been cryovac'd and when you open the bag, there is heaps of moisture. I don't know how the domestic types go in relation to moisture, but i do know that you have to reduce liquids / moisture to a minimum before you can seal the bag, otherwise i believe the liquids / moisture gets sucked into the pump and creates problems.
phill