mkory

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Is that pdf saying that if I brew a beer with sucrose, and ferment with S. cerevisiae (S-05), those yeast will break the sucrose down, then only eat glucose, leaving fructose behind?

Is this also why when increasing alcohol content, dextrose is recommended over table sugar?

GilaMinumBeer

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Not that I saw. Instead the the yeast will first ferment the glucose before it works on the fructose. so to speak.

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Hermit

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Yeah. It talks about the rates, but unless I missed it, doesn't talk about a difference in attenuation levels.

mkory

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So then back to my previous question...

With respect to the enzyme that the yeast uses to break sucrose down, I wonder what the amounts of this is and it's flavor contribution that would lead one to use an inverted sugar over table sugar.

Hermit

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Kind of the point of my original post. Some people claim they CAN taste the difference between using inverted sugar and plain. This didn't line up with the folks claiming that the PH in the wort automatically did the inversion anyhow.

ForRealBeer

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Here's a little about sugar conversion, etc. you might find interesting:

Inversion, Invert Sugar and Invertase

Invert sugars are monosaccharides, dextrose and fructose, that generally comes from sucrose, a disaccharide.

This is done by hydrolysis, and can be accomplished by heat, acid or the actions of an enzyme known as "invertase." Candy makers generally perform the latter process to make their invert sugars, and their source of invertase is our good friend Saccharomyces cerevisiae, aka brewer's yeast. S. cerevisiae makes invertase naturally.

How does invert sugar affect beer? Little if any flavor contribution, but what it does do is lighten the body of a given beer while increasing the alcohol content.

A side word about dextrose: it is more commonly called glucose and is the chief source of energy in the body and the main sugar that the body manufactures. Cells require insulin to utilize glucose.

So how does sucrose affect the flavor of beer? It must be broken apart before the yeasts can use it. As a complex sugar, it's a little harder for the yeast to "chew on" table sugar (sucrose) than it is for them to eat up dextrose or fructose.

A complaint often heard in homebrewing circles is that using table sugar in beer-making results in "cidery" beer, or sometimes even in a major amount of acetyaldehyde (green apple) being present. Acetylaldehyde is an intermediate compound in the formation of alcohol, and often results from using too much complex sugar that the yeast cannot fully convert. "Cidery" flavors are also indicative of acetylaldehyde, or aceto-bacteria, another problem entirely.

The rule pretty much became 'avoid all table sugar' for a lot of people. Others say that the aforementioned defects most likely come from poor yeast due to a under-pitching, a lack of other necessary yeast building materials in the wort, or even a lack of oxygenation. That makes sense if you think it through: not enough, weak or "tired" yeast won't finish its job properly and it can leave behind intermediate compounds that are quickly identified as off-flavors.

You can use table sugar and make great beers. But don't believe me, look around at some famous Belgian breweries who are world-renowned for their beers and you'll find a sizable number user table sugar instead of invert!

Table sugar can be used in small amounts in a healthy wort with few problems. But as the old advice goes about aspirin -- two is good for a headache, but don't take the whole bottle -- one should not rely on table sugars too heavily. Doing so courts the problems cider-beer and green-apple beer.

Me, I find it dead simple to make invert sugar and often do when I am brewing up a Belgian-style brew. Recipes galore exist all over the place, and it's only a short bit of work to make the stuff.

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avibayer

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What i have wondered, is that since glucose is the common starting molecule in the metabolic pathway of yeast, and a phosphorylated fructose is present later in the glycolitic pathway, what enzyme would be present to convert the fructose to 1-p fructose?

rayg

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Phosphofructokinase? I don't know what you mean by 1-p fructose
but according to the pathway at the KEGG database fructose is
phosphorylated by yeast at the 2 position, the 6 position and
both 1 and 6, but not 1 only.
http://www.genome.jp/kegg-bin/show_pathway?org_name=sce&mapno=00051&mapscale=1.0 &show_description=show

My mistake, 1-p fructose is on the far left, made in one pathway
from 1,6-diphosphofructose by phosphofructokinase, but also
from glycerone by another enzyme.

Click on the squares to get enzyme names and info, on the little
circles to get the molecular structure of the intermediates.

Ray

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avibayer

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I did not do that well in biochem, and my pathways get jumbled. The point i was trying to make is that the yeast seem to have the ability to tackle either pretty efficiently. I wonder if there is a significant taste difference as a result of the pathways.