The American Society of Brewing Chemists has released a study that finds saccharomyces cerevisiae has a nearly parasitic relationship with the brains of the people who interact with it most: brewers. It is a known fact that yeast is everywhere. It lives on our skin, on the skin of fruit, and even on the skin of manta rays. It lives in our guts and influences our digestion. But this is different. In his 2001 book The Botany of Desire, journalist Michael Pollan suggested that plants may evolve to seduce their human propagators into functioning as a reproductive mechanism, thus perpetuating their species. The ASBC findings have similarly concluded that ale yeast - which is a fungus - especially certain popular genotypes, has found a way to influence brewers’ choices of yeast selection.  Researchers performed numerous tests on brewers to confirm the hypothesis, which was first proposed by Dr. Patrice Adams, who does brewing research at the University of Vermont. A team of four scientists performed MRIs as well as presenting brewers with a battery of physical and mental challenges to confirm this yeast bias, as they call it. The results were shocking.“We found that yeasts with ester-positive genetics, specifically stone fruit esters, had a much stronger effect on brewers,” Dr. Adams said, “and that newer brewers were more susceptible than experienced brewers.” This fact is notable because the study found that exposure to other yeasts over time built up a resistance to the yeast’s influence. The MRIs concluded that certain yeast aromas lit up a part of the brain linked to excitement, addiction, and even arousal. The associated dopamine release causes the brewers to gravitate to those strains.  The challenges the scientists devised for the brewers were like something out of the LSD trials in the 1950s, but were critical to learning how fast the yeast get to work once the brewer is exposed. Repeated games of Memory with cards representing different yeasts and beers typically brewed with those yeasts showed that the brewers were more likely to remember where the pairs of parasitic yeasts were, relative to the other yeast strains. Double-blind sensory experiments with the brewers hooked up to brain scanners showed a range of preferences, illustrating the higher tolerance of more experienced brewers.“It’s like giving a regular coffee drinker an espresso versus someone who has never had caffeine,” said Adams. “The effect is there, but the experienced brewers responded more apathetically to the parasitic yeasts, even though they were present at the same levels as other brewers.”The strains of yeast in question are genetic variants of English yeast strains that have attained widespread use in the popular Hazy IPA substyle. Adams is working on a related study to determine if the yeast is responsible for Hazy IPA’s exponential rise in popularity. “Demand for Hazy IPA may be largely driven by the yeast itself, in order to perpetuate its life cycle.”