His take is that it has the same thing in it as Gas-X. I have read that too much can decrease residual bitterness by up to 10%.
Bottom line for me, I'm only using this in my yeast starters except for 1 boil that I tried it on and I don't plan on doing that anymore. As soon as I can grab some of the AT, I'll buy it and use it instead.The FDA says it should be unfiltered before drinking it and that does have me concerned. I'm still looking for Fermcap AT but it's not usually easy to find.
Here's the last thing I read a few months ago when we talked about Fermcap.
FermCap AT is a unique emulsion of an extremely effective surface active agent Dimethylpolysiloxane which prevents foam formation by reducing surface tension. FermCap AT is classified as a "Process Aid" because of its novel feature of being completely removed from the beer under normal processing conditions. It is adsorbed onto the surface of the yeast, vessel walls and filter media.
Analytical techniques accurate to 0.005 ppm cannot detect FermCap AT in finished beer.
FermCap S is a unique emulsion of an extremely effective surface active agent Dimethylpolysiloxane which prevents foam formation by reducing surface tension. It is used to control foam in kettle and during fermentation. It is completely removed from the beer after fermentation by the yeast and filtration. As a result of preserving hydrophobic beer proteins in solution it actually improves beer foam retention in the finished beer.