As far as leaching goes, a food grade polypropylene will not typically contain anything harmful that will leach into the mash at an unacceptable level (true for HDPE as well). The company can not label it as food grade if this was the case (this isn't China where companies can put melamine into dog food without regulation, or lead based paints on toys). The only thing I can think of that might leach into the mash would be a mold release agent that's there to help separate the liner from the mold during it's initial manufacturing process. Probably a food grade mineral oil or paraffinic compound that's easily removed with soap and water. There may also be some type of antioxidant or UV inhibitor to stabilize the polymer from high manufacturing temperatures or sunlight exposure. Again, these would be food grade and not pose a risk at the levels added. Look at some food labels and see how often you find BHT (butylated hydroxytoluene), yet you still eat this. Here's something else to think about: The residual component (terephthalic acid) used to make polyethylene terephthalate (PET) is in every plastic soda bottle because it leaches into the drink, especially the longer a bottle stays on the shelf. This is why a coke tastes different in plastic than glass or a can. Yet PET bottles are food safe.