 Prior to this time, bakers had been using old-dough leavens, and they had discovered that increasing the starter's rest intervals between refreshment promoted more yeast growth and less gas production due to overwhelming lactobacillus numbers.At some point bakers began to add brewer's yeast, or beer yeast or barm, to the refreshments which produced a whiter, sweeter-tasting bread.A shortage of beer yeast for making sweet-fermented breads developed when beer brewers slowly switched from top-fermenting to bottom-fermenting yeast (Saccharomyces pastorianus), and thus the Vienna Process was developed by 1846.