Natural or wild yeast is nothing more than the yeast we're all heard of, microorganisms classified as members of the fungus kingdom and it's the result of a spontaneous fermentation. Most people know it's used to make bread, among other bakery products, for it to rise and appear light and airy. Even though natural yeast was first in use, around 6000 years with the first records that show this use came from Ancient Egypt, it was discarded in the 1980s for the more practical and convenient synthetic or commercial yeast (also known as baker's yeast) that can raise dough faster.
You may wonder does this really make a difference. As with everything organic vs. artificial, natural ingredients are always better for you even when it's less practical. You can even make your own endless supply of natural yeast so in the end it's cheaper. The difference is all commercial yeasts started out as wild yeasts, and over time were selected for their traits, but the wild yeast kept more of those healthy traits.
Natural yeast breaks down harmful enzymes in grains, maximizes the nutritional availability of natural vitamins, minerals, and fibre in wheat, converts wheat into an easily digestible food which will not spike your blood sugar level. Natural yeast is both pre-biotic and pro-biotic, encouraging important good bacteria in the body. It discourages weight gain, and turns the phytic acid found naturally in wheat into a cancer-fighting antioxidant.
In baking, the yeast is used as a leavening agent, where it converts the food/fermentable sugars present in dough into the gas carbon dioxide. This causes the dough to expand or rise as gas forms pockets or bubbles. When the dough is baked, the yeast dies and the air pockets "set", giving the baked product a soft and spongy texture.
Wild yeast, or multi-micro flora are the natural air-borne ferments that are generated or seeded in a dough left exposed to a clean and cool atmosphere under specific conditions of moisture and temperature and the exclusion of larger specimen. Wild yeast also naturally enriches the bread, due to an additional development of nutrients by the beneficial enzymes and ferments.
Wild bread yeasts (and bacteria) are the basis of starter doughs (sometimes called sourdough starters) and are the same pretty much worldwide. The combination of yeasts and bacteria create a more complex flavour than using commercial yeast. Sourdough is much more versatile than commercial yeast. There are nutritional benefits, money-savings, and a range of flavours achieved when sourdough is used.
A natural yeast start is made by combining and fermenting yeasts with water and flour, and then keeping them fed and alive to use in baking. By combining the wild yeast with flour and water, an environment is created that allows the yeast to thrive and grow.
Not just for baking, natural yeast has been found useful for other things including supressing the gluten intolerance, especially good with the current rise of celiac disease – it all comes down to how natural yeast or sourdough starts break down the gluten in flour. There are many pros for using natural yeast, but it's also less practical in the baking industry, it takes longer to rise and the timing is not always the same. Nevertheless, if you have a chance to have sourdough instead of commercial yeast, be sure to do so and enjoy the taste.