Baker's yeast

Baker's yeast is rated 1 of 3 by SIGHI as 'yeast (fresh, dried, in all forms)', and no mechanism letter is set beside it. Those letters are how that list says WHY something is a problem — H for a high histamine content, H! for rapid formation, A for other biogenic amines, L for a liberator, B for a DAO blocker — and yeast EXTRACT two lines further down carries 2 and an L, so the blank here is a judgement and not an omission. A yeast cake is a living cell mass, not a food that has been standing while bacteria broke its protein down. What that column reports is perceived compatibility rather than a measured content, so it places this food without giving it a figure.

Baker's yeast is not what the MAOI diets restrict. Gardner names 'Marmite concentrated yeast extract' and Shulman names 'concentrated yeast extracts' — in both cases the autolysed paste, never the leavening cake — and Gardner adds the closing rule that foods it does not mention are unrestricted. SIGHI, which marks an A against every entry it holds to carry other biogenic amines, sets no letter against yeast in any form. Tyramine is what those diets restrict, and what they restrict it in are foods that have aged or fermented; a yeast cake is neither, being the organism that would do the fermenting. Both lists publish categories rather than mg figures, so this rests on which category the food falls in.

Baker's yeast stores its carbohydrate as trehalose and glycogen: Ertugay measured 8.6 to 33 mg of trehalose and 93 to 150 mg of glycogen per gram of biomass. Trehalose is two glucoses joined and glycogen is a long glucose polymer, so neither is a fructan, a galacto-oligosaccharide or a polyol. That measurement covers what the cell STORES, and a yeast cell is also a wall, which is why this sits at low rather than none. The figures come from cells grown in a fermenter at set dilution rates, where the trehalose moves with the growth conditions rather than staying fixed.

Baker's yeast is grown on beet or cane molasses, and a yeast cell takes up the trace metals its medium carries, nickel among them — the same route that puts yeast extract high. What separates the two is concentration: the extract is the contents of many cells reduced to a paste, while this is the cells themselves, and a dough takes one to two per cent of the flour weight in yeast. The molasses varies with its crop and its refinery, so the nickel a batch carries follows where it was grown.

Baker's yeast is a fungus, and fungi are not oxalate-free: Savage measured cultivated mushrooms at 58.9 to 104.1 mg of total oxalate per 100 g of dry matter. Those are mushrooms and not yeast — a different organism and a different tissue — so they establish that the class is not empty rather than what a gram of yeast carries. The quantity is what holds this down: a loaf is leavened with a spoonful.

Baker's yeast holds no free fructose. Ertugay separated what the cell stores and found trehalose and glycogen, both built from glucose alone. Fructose is what this organism CONSUMES rather than keeps: it is half of the sugar a dough feeds it, and the rising of the bread is that sugar disappearing.

Baker's yeast holds no sucrose. What Ertugay found stored in the cell is trehalose and glycogen — 8.6 to 33 mg and 93 to 150 mg per gram of biomass — and sucrose is not among them. In a dough the sugar goes the other way: it is the yeast's fuel, not its reserve.

Baker's yeast holds no sorbitol. The two carbohydrates Ertugay measured in the cell are trehalose and glycogen, and neither is a polyol — a polyol is a sugar alcohol, which is a different molecule from a sugar and from a chain of them.

Baker's yeast holds no oligosaccharide. Ertugay measured the cell's two stored carbohydrates and both fall outside that length: trehalose is a pair of glucoses, too short, and glycogen is a long branched polymer, far too long. Neither a fructan nor a galacto-oligosaccharide appears among them.