I've been working in a molecular biology lab that uses yeast cells for most experiments, and one of my duties is to maintain the solutions for feeding these creatures and the media they grow on; various powdered yeast bits and proteins and agar. When first I was exposed to Marmite, I realized that the smell is identical to that of YPD (yeast-peptone-dextrose) or Luria broth. Needless to say, I didn't dare taste it.