Kemisk reaktion i hhv. overgær og undergær ved ølbrygning.

http://howtobrew.com/book/section-1/yeast/yeast-types

Det er det samme jeg kan finde ud af - det er bare ikke det jeg søger.

Jeg søger en kemisk forståelse af forskellen mellem overgær og undergær.

F.eks kan jeg forestille mig at den ene gær har flere Ilt-bindinger i udåndings-gassen end den anden - derfor flyder den mere frit rundt uden at synke til bunds.

Det er kemien bag jeg søger

https://www.reference.com/science/chemical-reaction-between-yeast-sugar-fb04a3807cdd557f
The balanced chemical equation for this reaction is glucose/sugar (C6H12O6) in the presence of the yeast enzyme zymase reacts to produce 2C2H5OH (ethanol) +2CO2 (carbon dioxide). This is the ethanol fermentation process used to make beer, wine and bread.
At der er 2 typer gær (ale / lager) som er top/bund har ikke noget med kemien at gøre.

If one must point to a single differentiating factor between ales and lagers, this is it. Ales and lagers are fermented with two different species of yeasts. Ale yeast, Saccharomyces cerevisiae, is, in fact, the same species of yeast we use to bake bread, which ought not be too surprising given the close historical relationships between brewers and bakers.

Saccharomyces pastorianus is, however, a microbe all its own. Aside from its obvious penchant for the cold, S. pastorianus also has the ability to metabolize melibiose and raffinose, two complex sugars that S. cerevisiae can’t really deal with. The practical implications of this metabolic capacity are not great, for malt-based wort contains very little in the way of melibiose, and no raffinose whatsoever. Nonetheless, it’s important from a taxonomic standpoint in that it supports the distinction of ale and lager yeasts as unique organisms.

Ok - så nu har jeg 3 nye informationer at komme videre med.

"has the ability to metabolize melibiose and raffinose, two complex sugars that S. cerevisiae can’t really deal with."

metabolize er - så vidt jeg husker - fordøje.

Så melibiose og raffinose er forskellige sukker-arter, som cereviasae ikke kan omdanne - ergo giver det mere smag/kompleksitet til øllet, hvis man bruger pastorianus?

Og hvorfor er den ene en flyder? Og den anden en synker?

Jeg giver dig point allerede nu, da jeg synes jeg har fået nogle fede oplysninger*S*

Takker for det.