I had a look at this subject a few years ago and the feedback was that it was done to circumvent the original patent .
The original patent mentions salt in the "recipe" ,this maybe enough as get around it ,
Salt water activated MRE heaters ??
Re: Salt water activated MRE heaters ??
The inventor of the FRH did it from the beginning with salted water. The military changed it to make it working with "any" water from canteen, out of a river, rain etc..