Easy way to tell if mash is converted

[AstroBrew]

So I've been doing a lot of low temperature mashes lately to dry my beers out. While I'm a patient guy, I was starting to wonder if I really needed to wait 90 minutes to get complete starch conversion. I've never bothered with iodine tests as it seems a little too subjective for me. But then I got thinking, conversion is complete when I've got the right amount of sugars dissolved in the mash. And what do we all know sugars do in solution? Increase the density! This I can objectively (and easily) measure. So what should the gravity be for a converted mash? That's easy too. You could go the detailed route and take the pre-boil gravity your software computes for you and correct for the mash liquor volume and efficiency such that:

converted mash gravity points = (pre-boil gravity points) * (pre-boil volume) / (decimal efficiency) / (mash liquor volume)

For example, if I want a pre-boil gravity of 1.050 and volume of 7.5 gallons with 75% efficiency and 5.25 gallons of mash liquor, my mash SG should be 50 * 7.5 / 0.75 / 5.25 = 95, or a SG of 1.095. Correct that for temperature and get out your hydrometers!

Now, I realized after the fact, it's even easier than the calculation above. To get pretty close, just assume an extraction of 36 gravity points per pound per gallon from your grist and divide by your liquor to grist ratio in gallons per pound. So, I used a ratio of about 0.38 gallons per pound, so my mash gravity points should be 36 / 0.38 = 95! Conveniently, this number is the same for every mash, independent of grist composition, that uses a liquor-to-grist ratio of 0.38 gallons per pound (that's 1.5 qts/lb, btw). Just correct for the appropriate temperature and Bob's your uncle.

This helped me out last night while brewing. I was mashing at 149F and wanted to know if I should really wait an extra half-hour beyond my normal 60 minute mash. At 60 minutes, I measured a mash SG of 1.078 and so I waited. At 80 minutes, I measured an SG of 1.098 and so I started sparging. So, I guess to answer my question above, in this situation I did need a longer mash to get complete conversion. I'm thinking this little trick will save me some time with higher temperature mashes where conversion happens much more quickly. Maybe it will only save me a half-hour on brew day, but hey, why waste precious time?

I'm sure this is not a new thought, but I hadn't heard of it before and it's so simple and useful that I thought I'd share. For me, it takes the guess work out of deciding if the mash is fully converted.

Cheers!

 

[Yooper]

Good idea. I'm happy with an iodine test, though.

 

[anastasis]

Aren't complex carbohydrates in suspension going to throw off your gravity numbers? The gravity may be increased, but that is not going to indicate conversion as the increase could be due to unfermentable sugars in solution.

 

[Funkenjaeger]

I've never bothered with iodine tests as it seems a little too subjective for me.

Perhaps you should at least give it a try before you make up your mind. I find the iodine test to be pretty straightforward - it either changes color or it doesn't. It's cheap enough to grab a bottle from your local pharmacy, and you can try it in parallel with your method, if nothing else...

Calculating target first runnings SG and then taking multiple SG readings sounds like quite a bit more effort (though not too bad with a refractometer)

 

[malkore]

My iodine shows conversion in 40 minutes with briess 2-row. I'm not getting any more sugar out letting it sit longer.

sparging better, sure.

 

[artbrau]

How do you mean "subjective?" No color change, no starch. Period.

 

[Steelers77]

I am usally converted in 35 min using Breiss, I also do an iodine test.

 

[nebben]

Simple chemistry is hard to beat. Ditto on the iodine test.

 

[oceanselv]

+1 on the iodine test. A simple test we learned how to do in Chem 101.

 

[passedpawn]

Iodine test always worked for me. I don't bother anymore because it was pointless if the temps were good.

 

[Professor Frink]

There were a lot of numbers in there. If I'd say I prefer an iodine test, I'd be lying too. After an hour, it does into the keggle.

 

[pjj2ba]

I've used my refractometer to follow conversion. I do a lot of step mashes, and by checking the gravity it helps me to nail down when to begin the next step. This helps me in reproducibility. This way, say, I want to do a step after I've reached 85% conversion. A quick check with the refractometer will tell me this and is more reliable then assuming that if it took 30 min. the last time, it will be 30 mi. this time. (Although my goal is to have it take 30 min. each time as part of my trying to improve reproducibility).

If I had a spectrophotometer at home, then I could use iodine to do this, but I don't.

 

[BuzzCraft]

Aren't complex carbohydrates in suspension going to throw off your gravity numbers? The gravity may be increased, but that is not going to indicate conversion as the increase could be due to unfermentable sugars in solution.

bumping this question, since no one has addressed it.

intuitively, i would think so, as well. i'm curious what someone who knows more than I has to say about it.

Isn't it accurate to say that a mash held at 154F will end up with different percentages of dextrins, depending on whether the mash was held for 30 minutes, 60 minutes, or 90 minutes?

So, even if one gets complete conversion by 35 min, it might not be the fermentability profile (and hence beer body profile) you're looking for at a give mash temp?

 

[starrfish]

I'm not that smart. A drop of iodine, no color change, good to go.
Last batch had conversion in 45min with marris otter, but let it ride the full hour. What's an extra 15 mins, right? been getting 76-78% efficiency at 1 hour. I'm ok with that range :rockin:

next time I brew I may go to a 90min mash and see if it changes efficiency. I doubt it, but worth checking.

 

[ColoradoXJ13]

This method is not going to tell you if your mash is done, all it will tell you is that you extracted the total soluble materials out of your grain that you expect (efficiency), the hydrometer cannot differentiate between dissolved starch, long chain sugars, dextrines, and fully converted sugars.

 

[AstroBrew]

bumping this question, since no one has addressed it.

Isn't it accurate to say that a mash held at 154F will end up with different percentages of dextrins, depending on whether the mash was held for 30 minutes, 60 minutes, or 90 minutes?

So, even if one gets complete conversion by 35 min, it might not be the fermentability profile (and hence beer body profile) you're looking for at a give mash temp?

I think this is a good point. If I understand the results of this experiment by Kai:
http://braukaiser.com/wiki/index.ph...ity_and_efficiency_in_single_infusion_mashing

a longer mash at a given temperature yields a more fermentable wort (see figure 6). And it is true that just because the density has increased, it doesn't mean that what's in solution is sugars, fermentable or otherwise.

And I do realize that the iodine test is a better way to check conversion. I just don't have any and I keep forgetting to pick some up! But now I am wondering, if you have unconverted starches in solution and you mash-out to stop enzymatic activity before those dissolved starches are converted, what does this mean for your wort? Will the starches be carried through the boil and into the fermenter where they will not be metabolized by the yeast?

(underlying question: Is this why I am having attenuation issues )

 

[big supper]

This method is not going to tell you if your mash is done, all it will tell you is that you extracted the total soluble materials out of your grain that you expect (efficiency), the hydrometer cannot differentiate between dissolved starch, long chain sugars, dextrines, and fully converted sugars.

That's what I was going to say too.

 

[pjj2ba]

Aren't complex carbohydrates in suspension going to throw off your gravity numbers? The gravity may be increased, but that is not going to indicate conversion as the increase could be due to unfermentable sugars in solution.

Anything that is merely in suspension will not affect the gravity reading. Only things that are dissolved contribute to the specific gravity.

Also for refractometers, I'm pretty sure that the soluble dextrins won't have a big impact on the brix reading. They will affect a hydrometer reading though

 

[Cliff897]

Have you tried the iodine starch test?
Unless one has some color blindness issues (& more males do than females) it's pretty obvious.

 

[IrregularPulse]

Ditto, sounds like a lot more work than an iodine test, but some people like that so to each there own.