Contact your boiler chemical vendor and ask them for documentation that the treatment chemicals and dosage rates are FDA/USDA approved. If they cannot provide the documentation, or cannot supply a suitable approved chemical ~ find another vendor that understands all the criteria for your application including product liability.
Do not use the steam generated from the normal boilers. Use normal steam for indirect heating in stainless steel steam systems to generate the food quality steam. The quality of water should also be monitored accordingly. This system may be more suitable and economical for small but quality steam requirements.little low dryness factor shall also not be alarming.
I work in a Canadian Manufactucturing facility that ships to the US, so we are subject to the FDA regulations and requirements. My QA manager has a more intimate knowledge than I do of "Food Grade" and the discussions we have had revolve around "culinary steam". This applies to steam that is to be applied into food directly as part of a cooking process, as opposed to food in indirect contact (thermal vessels).
The requirement states a required filter size (I'm not sure what it is, exactly - by definition, 95% of particles 2 microns and larger must be removed) and that only stainless steel piping be used between the filter and the product.
If this is not your question, my apologies for the waste of time and space.
Food grade steam requires DI water and the process of producing the steam is in food grade equipment as you can contaminate the steam if you do not keep to spec.