Ultraviolet (UV) light is a type of radiation that generally has negative consequences on living cells. However, UV light has the opposite effect on yeast, as the rays can yield increased yeast productivity. The experiments into this interaction between UV light and yeast began in 1920.
Increased Growth and Reproduction
A 1940 study at the University of St. Andrews published in the "BioChem Journal" definitively concluded that UV light exposure releases nitrogenous material from yeast cells. Most of this material is an amino-N substance, which, when released into the surrounding medium of the yeast cells, facilitates their growth and reproduction. This coincides with the results of a 1923 study published in the "University of Chicago Press" that also demonstrated that UV light exposure increases yeast production. In that study, brewer's yeast exhibited a faster rate of fermentation.
UV light does slowly penetrate and destroy the cell membranes of yeast. This process is the likely cause of the cells' release of nitrogenous materials. Similar materials are also released by yeast cells during the outright destruction of cell membranes by other methods. However, UV exposure, when controlled, initiates, but does not complete, cellular breakdown. This has the benefit of releasing growth-inducing compounds into the yeast environment while keeping the cells intact.
UV light, in large quantities over longer periods of time, does kill yeast cells eventually. A 1920 study published in the "Botanical Gazette" noted that yeast does have a threshold after which it dies from overexposure to UV light. This threshold depends on the strength of the UV light source and the time of exposure. The study noted that as little as three minutes' exposure can kill yeast from high UV light strength, while the University of St. Andrews study exposed the yeast to six hours of UV light, which killed 60 percent of the yeast cells. Thus, a balance between UV intensity and exposure time is necessary for the irradiation to yield desired results.