Yep, Beverage People has it. The black on tomatoes is a fungus most likely. It's not just on the surface. Kmeta would kill it, but it would need to penetrate the entire fungal colony, which would take a long time and would saturate the tomato. I'd advise against it. For tomatoes like that, I usually cut away the black and cook them into sauce or salsa. I try to use the freshest produce for dehydrating.
The downside of using Kmeta is the sulphur. Commercially for produce like apricots, they use sulfur dioxide usually because it's cheaper. They basically burn sulfur and let the smoke come up, which gives it a pretty heavy dose, much heavier than a regular Kmeta wash. I use a minimum amount of sulfur in the form of Kmeta, and then I rinse with water to get it out, and then I use the citric. And I have no issues with sulfited produce, but some do and have bad allergies.
When you see dehydrated stuff marked unsulphured, most of the time they use only citric instead. Frankly, I don't consider it a big deal because I'm not allergic.
