Hello,
When working with GNS, we found that some "rubber" material used for seals are not alcohol-proof even though the manufacturer say they are "fit" for alcohol use. There is chemically-speaking a huge difference between a 10% abv mash and 95% GNS. Based on our experience, material like nitrile, viton and teflon tape are not suitable when used with 95% alcohol for a prolonged period of time. We did a simple test by putting a small seal in a jar with a 50 ml of 95% alcohol for a week, then rectified the alcohol to 40% by using RO water. Attached is the result for nitrile, viton and teflon tape. Nitrile creates the most opaque solution.
What rubber material should we go for to prevent this? We are about to do the same test with a silicon seal.
Chris