Measuring Fermentable Sugar in Wort?

I am trying to find out there is a simple way to measure the levels of fermentable sugar in my wort. No I'm not talking about using a hydrometer or refractometer to measure the total sugar, I'm only interested in the fermentable sugar (e.g. maltose, sucrose, fructose, glucose, galactose ...).

My interest primarily stems from a few batches that seem to have stopped early for unknown reasons. Typically this is caused by yeast problems (not enough, wrong temp, inadequate oxygen or nutrients) or lack of fermentable sugar. I can make educated guesses about why, which usually decides my next course of action, but I would like to know with more certainty what the problem is before attempting to blindly fix it.

Thus, my first thought is to determine whether my mash has somehow left me with a significant amount of un-fermentable sugars. To do this I presume I would need to at a minimum measure the proportion of fermentable sugar with the amount of total sugar. The delta would hopefully give me a good approximation of un-fermentable sugars that exist.

I was hoping there might be a kit to do this, but I can only find ones for wine that detect levels of glucose and fructose (monosaccharides), which doesn't help much considering wort has mostly maltose ( a disaccharide). So the options as I can see them would be to find a method for measuring the disaccharides in solution or find some kind of disaccharidase enzyme to help break down the disaccharides into monosaccharides for analysis using the Wine kits.

Any suggestions would be appreciated.
Thanks,
Jaime

BTW - The brew that initiated this post is a 1.082 SG Saison being fermented with WL565 yeast. The sugar extraction was much higher than expected so I am a little low on yeast. I mashed for 90 minutes at around 143-145 to improve extraction of fermentable sugars. I added two lbs of dextrose, so I know at least that sugar is fermentable. After two days the gravity dropped 1.022 SG to 1.060 SG, but the bubble rate is now very slow (once every 15 seconds) and there is little activity on top of the wort in the fermentor. Fermentor has always been kept in the 80-85 degree range, which is what I have read this yeast likes. I know saisons slow down after a few days, but this seemed too aggressive of a slowdown, so I wanted a way to determine if I screwed up the mash (which seemed to go very well).

I know this isn't that helpful. But it's a start. You could use a turbo yeast on a sample of your wort. Keep it really warm and let it ferment out. This should give you a pretty good idea of lowest possible FG of the wort. Hardly scientific, but somewhat effective. You could use a stirplate for the sample too, that should help make sure the yeast eat every possible bit of fermentable sugar without settling out.

Big beer requires more yeast and yeast that can handle alcohol well. Lower mash temperatures favor fermentable sugars longer mash time also favor fermentable sugars. So if you were high temp mashing then that would explain part of why the yeast would not attenuate as much. What temperature did you pitch yeast at and how much did you use. Did you hold the temperature constant during the primary fermentation. A roller coaster fermentation temperature does not help either.

iodine test for conversion before lautering?

If you're not getting the enzymes to convert the starches to sugars, your not going to get the yeast to eat many of them. A iodine test positive for starch will confirm that it is in fact large chain dextrins in you wort.

Mashed at 143 for 90 min. Used two vials of WL565 in 3 liter starter on a stir plate for 2 days prior. Pitched at 75 degrees. ETC raised temp to 82 and held.

All signe lead me to yeast problems, which is fine, I just want to know for sure by measuring the sugars. Which is why I asked if anyone knew a way of accurately measuring it.

Thanks.

> iodine test for conversion before lautering?

Good point. I have never used the iodine test before, but had planned to use it for future brews.

Whats the best way of doing this? Is there a kit I can buy or do I just need some iodine.

Thanks.

jvetter;

quick Q: is this something that you observed on your Saison or is this an issue with all of your brews?

At first blush, I would say you underpitched for a 1.082 batch but I've never brewed Saisons before.

I would go download Jamil's Saison podcast, I distinctly remember it and he had alot of good tips about brewing Saisons...things that wouldn't occur to someone experiencedin brewing more common beer styles. IIRC, he suggested to start the fermentation out relatively cool and ramp the temp up at the end. I think it had something to do with preventing the yeast from getting too stress at the beginning of fermentation and dying out leaving you with a high gravity (similar to what you observed). Something to do with the yeast producing fusel alcohols...?

good luck...btw...I don't think its your mash procedure and something to do with the ratio of fermentable to non-fermentable sugars....nothing that complicated!

jvetter said:

> iodine test for conversion before lautering?

Good point. I have never used the iodine test before, but had planned to use it for future brews.

Whats the best way of doing this? Is there a kit I can buy or do I just need some iodine.

Thanks.

Click to expand...

https://www.homebrewtalk.com/wiki/index.php/Iodine_test

jvetter said:

I am trying to find out there is a simple way to measure the levels of fermentable sugar in my wort. No I'm not talking about using a hydrometer or refractometer to measure the total sugar, I'm only interested in the fermentable sugar (e.g. maltose, sucrose, fructose, glucose, galactose ...).

Click to expand...

This is probably the test you are looking for:
http://braukaiser.com/wiki/index.php?title=Fast_Ferment_Test

broadbill said:

jvetter;

quick Q: is this something that you observed on your Saison or is this an issue with all of your brews?

At first blush, I would say you underpitched for a 1.082 batch but I've never brewed Saisons before.

Click to expand...

I've had 1-2 out of 15 brews that needed beano due to presumed unfermentables, but nothing like this.

I underpitched a little because I was expecting 1.072 and got 1.082, but I wouldn't expect this kind of slowdown.

I will continue to monitor the progress, maybe it will just be slow from here on out. Guess I will know in a few days after a get some readings whether its the slow saison yeast or another problem.

The thought of the yeast dying did occur to me, but didn't seem likely given the description of the yeast in the Farmhouse ale book I read. The book indicated that temperatures in the 70's could actually slow the yeast because they prefer 85 to 95 (ouch!).

*edit: flyguy beat me to it...*
Kaiser recommended a "fast ferment test" to me when I was worried about the fermentables I was getting from the mash:
http://braukaiser.com/wiki/index.php?title=Fast_Ferment_Test

I did it with my last batch - I took enough wort to easily fill a hydrometer jar (and then some), stuck it in a flask, pitched a big scoop of bread yeast, and gave it a good swirl. It fermented out in like a day, down to 1.011 or so, and the main batch fermented to roughly the same thing (though obviously it took longer), so it seems like an accurate measure.