Sugars Sugars Sugars

I have a few coneptual questions abouts sugars....
I know a fair amount I already I suppose. I know about monosaccharides, disaccharides, etc. I also know that yeasts can only metabolize certain sugars as well.

1) are disaccharides the most complex sugars yeast can metabolize?
2) do yeasts react equally with mono/disaccharides and also the different isomers? or better...would pure maltose or pure sucrose would yield the same effect?
3) do yeasts metabolize all of the sugar in a batch of beer, or if there is an overloaded amount where metabolizing it all would take forever. (assuming you have enough yeast propagated already so as not to have a slow fermentation from the crabtree effect)
4) Does yeast only rely on sugar for fermentation? (if you throw so yeast in some water with dissolved table sugar will it produce alcohol? not that this experiment is worth anything)

anything else you feel like stating for knowledge purposes would be great.

I'm going off the top of my head here:

Yeast metabolize monosaccharides better then disaccharides, which I was under the impression that they don't handle as well. I am unsure if different isomers of the above are handled differently by yeast or not, as I don't recall ever reading a comparison.

Yeast use oxygen or sugar to function. Once oxygen supply has run out, the yeast switch to anerobic function, producing CO2 and ethanol from sugars.

One nice thing is that with all-grain, you can control the ratios of the different sugars produced from the malted grains. Different mashing temperatures activate seperate enzymes, which in turn produce different suger molecules from the grain starches.

Here's a decent article from BYO that covers the different enzymes.

Good post LupusUmbrus. This will help alot of AGer's.

LupusUmbrus said:

I'm going off the top of my head here:

Click to expand...

Showoff.

Thanks for the article...I for one need to read up on those things. It's nice to know why we do the things we do.

After further research, it looks like my earlier assessment of how yeast react and use different types of sugars was partially incorrect.

Since alot of this relates better to the all grain process, and I have a related topic in the AG forums, I'm leaving a link here to that post.

Fermentability - mashing, the sugars produced, and how yeast eat them

Yeasts will consume sugar until the alcohol content is too high for them to continue. Most ale yeasts "hit the wall" around 7-8% ABV. Wine yeasts can go as high as 15-16%. Saki and distiller's yeasts can handle 18-22% (I've seen claims of 24%, but not on a commercial product) An 8K distiller's yeast will eat its' way through 8KG of sucrose per 25 liters of water. In all cases, if there is sugar left over, there's sugar left over.

A distiller's yeast can live on water and sucrose, but a commercial yeast food can give you a better/faster ferment. I'm going to try some to finish my next batch of barley wine. I'll split the batch after the primary fermentation and use 8K on half and champaign yeast on the other half. Both a neutral yeasts, but the 8K should finish much faster.

david_42 said:

Most ale yeasts "hit the wall" around 7-8% ABV.

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Is this independent of the pitching rate, or will a higher pitching rate help reach the higher abv's?

independent. the high alcohol content kills the yeast (or maybe it just shuts it down). Either way, the yeast stop working in those conditions, no matter how many of them are in there.

-walker

Two solutions to turn sugar into easily fermentable sugar:

Alpha-amylase enzymes will break down the unfermentable sugars to make sure that everything is fermentable. Of course, these may take up to three hours to completely work at below 140 degrees. Above 140 deactivates them.

Koji (Apsergillus Oryzae) is used to make japanese rice wine, and will convert sugars in ten-twenty minutes at 100 to 120 degrees.

The happy mug said:

Two solutions to turn sugar into easily fermentable sugar:

Alpha-amylase enzymes will break down the unfermentable sugars to make sure that everything is fermentable. Of course, these may take up to three hours to completely work at below 140 degrees. Above 140 deactivates them.

Koji (Apsergillus Oryzae) is used to make japanese rice wine, and will convert sugars in ten-twenty minutes at 100 to 120 degrees.

Click to expand...

You're on the right track there.

Beta-amylse gives you you're most fermentable wort, optimal temps ranging from 140 - 149 degrees. Only catch is that it requires the starches to be broken down a little before it can work on them.

Alpha-amylse produces you unfermentable sugars. It also does the initial breaking down of starches required by Beta. Optimal temps are around 154 - 159 degrees.

Note that both enzymes are active outside their optimal temp ranges, but do not work as quickly.

LupusUmbrus said:

Alpha-amylse produces you unfermentable sugars. It also does the initial breaking down of starches required by Beta. Optimal temps are around 154 - 159 degrees.

Click to expand...

Now this is interesting. Does this imply that, if you're going to do a multi-step rest, you should actually do the alpha before the beta if your goal is to produce a dry product with lots of fermentables? I've never heard of a mash being cooled down from 155 to 140 as "step 2", but I suppose it could be done. Would the beta-amylase be destroyed by the higher temperature of the alpha rest, or just deactivated so that it could be turned back on when the temperature drops?

Edit:

Ahh, the BYO article actually answers my question:
"Many brewers, when first starting out, get what seems like an ingenious idea that will not work. The idea is start out at 158° F to let alpha-amylase do its thing and then to cool the mash down to le beta-amylase do its thing. This won’t work because heat denatures enzymes at temperatures above their optimum, and denaturation is permanent."

This decoction thing seems like a better idea all the time.