Do you mean fermentation?

There's a nice write-up about it in the seed saving FAQ's, Here.

Welcome, Johnny! Here's what I'm thinkin' 'bout the dealio. What kind of tomato is that 'un? If it is a hybrid tomato, you might be disappointed at the results. If is an heirloom (aka open-pollinated) type. This website is a rich source of knowledgable people, so take advantage of it.
And for Pete's sake, if you fail, try again, and again... Nobody ever learned all this stuff overnight.
And most of all, remember.. "Nature, to be commanded, must be obeyed."

Best!

whoops, having trouble posting my followup. homegrown back.
followed a cool link and found this gal's blog and she has some wicked good Utuube snippets about this subject.
http://happyhobbyhabit.blogspot.com/

just follow that link and enjoy.

I guess it is fermentation. I'll read it thanks. I just mean I'm eatin' a tomato sandwich and like it. I save one of the seeds from it and grow a plant from it. It just interested me.