Yeast can naturally produce Vitamin D by reacting to the ultra violet light of the sun in a similar way as humans do. When that happens, natural sterols in yeast are converted to vitamin D. Bakers yeast Saccharomyces cerevisiae naturally contains ergosterol. When exposed to UVB light, this compound is converted to ergocalciferol (vitamin D2).
In order to offer a natural and vegetarian source of vitamin D, Lallemand has developed a process to treat yeast to a UVB light and become rich in vitamin D2. In baked product formulations it can be added with the other ingredients to be used as a source of vitamin D.