I don't use a commercial defoamer, I use canola oil. My foam issues are usually with the very first batch that goes into the evaporator and after that I have very minimal foaming issues. I normally don't have any issues with the filter press when using it and I don't believe that using defoamer affects the amount of nitre in the sap. That is based on a yearly thing with the trees themselves.
2004 - 2012 2x3 flat pan 25 to 60 taps
2012 2x3 new divided pan w/draw off 55 taps
2018 - didn't boil surgery - bought new evaporator
2019 new SML 2x4 raised flue high output evap. 65 taps
made 17 gal. syrup
2020 - only put out 53 taps - made 16.25 gal. syrup
2021 - Didn't work out
2022 - 25 taps on bags / 8 taps on 3/16's line - late start
2025 - No tapping for me