Salts? You probably have more in your tap/well water... not sure. I only use R/O water so there's not much in there to begin with.
The information comes from making Saki. Rice doesn't have much nutrition for yeast so the standard 'feed' people have come up with is epsom salts and Potassium chloride. The rice is molded with a specific white mold to make Koji... this breaks down the natural carbs into simple sugars. The Koji is then added in a several batches to feed the yeast as the primary fermentation goes along.
Fun stuff! *grin* Making Miso and Tempeh is also something I do... fermentables are awesome! Saurkraut and Kimchi for the wife and kid (I'm "A" blood type... cabbage instantly increases mucus production) and Northern Bean Tempeh for everyone (neutral bean for all blood types... Yeah!)