OK... "Yeast is a single-celled living organism that transforms sugar and starch into carbon dioxide and alcohol through fermentation."
From Wiki "A yeast is any species of fungus that grows primarily in a unicellular form and reproduces via budding or fission. Yeasts are eukaryotic microorganisms that originated hundreds of millions of years ago, with at least 1,500 species currently recognized."
The two yeasts I have happily interacted with are bread yeast and brewers yeast (the wine version). Beer yeast is better at attracting slugs than bread yeast, although the two are more similar than some other yeasts. Wine vs cider yeasts can be quite different.
There are also nasty yeasts out there - ones most humans would prefer not to interact with. I've never had a "yeast infection" but I've definitely heard of them.
So if you're dealing with really dead soil, and don't have access to some quality compost to make compost tea, any sort of yeast for making bread, beer or wine, would probably be better than nothing. However, you might do the soil more good by finding some good local dirt, digging up some worms, and introducing those to either some near finished compost, or your plants with some compost spread around them. I've been told that worm guts have lots of microbes of all types in them (sort of like human guts, but we've got a few dangerous ones like e-coli) and that as the worm poops, those microbes will inoculate the soil.
So I don't think the idea isn't helpful - I'm just suspicious that there might be better ways.
