Definition of tae kwon do for English Language Learners. : a style of fighting that originated in Korea and that uses kicks and punches but no weapons. Britannica.com: Encyclopedia article about tae kwon do.
It is also used in the baking process as a leavening agent; yeast releasing gas into their environment results in the spongy-like texture of breads and cakes. Because of its role in fermentation, humans have known about and used Saccharomyces cerevisiae for a long time.
Yeast is a single-celled organism and only certain strains are used for fermenting grain. Yeast activation and the initiation of fermentation are triggered by hydration, from either water or some other liquid, and the presence of a food source. Fermentation ends at 140 degree F during baking when heat kills the yeast.