Mash gravity

[MFigz]

I'm color blind, so doing the iodine test usually requires me to ask my wife or kids if conversion is complete. Normally I brew when no one's home, so I just mash extra long to ensure that it's done.

During my last Brew, I got to thinking... shouldn't specific gravity keep rising until mash conversion is complete? Is there any reason I can't take refractometer samples to determine when to begin sparging? Fyi, I have a herms setup, so I would think gravity should be pretty consistent throughout the mash tun since it is constantly recirculating.

Thanks,
Mike

 

[rburrelli]

Your theory sounds correct, but I don’t know enough to tell you whether it would work. I will be checking back on this though because it is very interesting approach.

 

[kevin58]

The more you brew you will find yourself not bothering with certain steps. I no longer take gravity readings two or three days in a row to confirm the end of fermentation. And I no longer do iodine tests to confirm starch conversion.

That being said... the more I brew I do find myself being even more particular about some steps too. I am much more particular about building up yeast starters. And I am make sure my strike and mash temps are accurate.

 

[doug293cz]

I'm color blind, so doing the iodine test usually requires me to ask my wife or kids if conversion is complete. Normally I brew when no one's home, so I just mash extra long to ensure that it's done.

During my last Brew, I got to thinking... shouldn't specific gravity keep rising until mash conversion is complete? Is there any reason I can't take refractometer samples to determine when to begin sparging? Fyi, I have a herms setup, so I would think gravity should be pretty consistent throughout the mash tun since it is constantly recirculating.

Thanks,
Mike

Yes, this works well. This method is more reliable than the iodine test. You can even calculate your conversion efficiency (mash efficiency = conversion efficiency * lauter efficiency) using the mash SG measurements.

Brew on

 

[RM-MN]

Stir well before you take every refractometer reading if you want to know when conversion is done. I use the plastic pipette to take a sample and the gravity will increase the farther down into the wort I reach.

 

[Vale71]

This method will not work. If it did then why would professional brewers still bother with the iodine test?

The reson this will not work is that conversion does not change gravity. To achieve conversion you need first to gelatinize the starch and then enzymatically convert it to dextrines. Conversion does not change weight. This means that if you have 10 grams of starch per 100 grams of liquid you will measure 1 degree Plato. If you then convert those 10 grams of starch you'll have 10 grams of sugars per 100 grams and still read 1 degree Plato. Any intermediate situation (i.e. partial conversion) will still result in the same gravity reading and is totally unreliable as far as verifying complete conversion goes, hence the need for a iodine test.

 

[doug293cz]

This method will not work. If it did then why would professional brewers still bother with the iodine test?

The reson this will not work is that conversion does not change gravity. To achieve conversion you need first to gelatinize the starch and then enzymatically convert it to dextrines. Conversion does not change weight. This means that if you have 10 grams of starch per 100 grams of liquid you will measure 1 degree Plato. If you then convert those 10 grams of starch you'll have 10 grams of sugars per 100 grams and still read 1 degree Plato. Any intermediate situation (i.e. partial conversion) will still result in the same gravity reading and is totally unreliable as far as verifying complete conversion goes, hence the need for a iodine test.

Conversion doesn't change gravity by much, but it does change it. Saccharification consumes one water molecule for each starch bond broken, and those water molecules become part of the two new molecules created by the bond breakage. In a typical mash the sugar will pick up about 3.5 - 4.0% additional weight compared to the starch it was made from. Obviously this change is not large enough that it could be used as an end point indicator.

My understanding is that the rate controlling (slowest) step in the mashing process is gelatinization, and that saccharification proceeds relatively rapidly once the starch goes into solution. Gelatinization can be sped up by using a finer crush, but that will not speed up saccharification. So, if saccharification is significantly faster than gelatinization, you did a mash with a fine crush that reached max wort SG in say 10 minutes, and proceeded directly to a boil (to stop enzymatic action), then you should not have a high FG after fermentation. If on the other hand, saccharification is the slow process, then the 10 min fine crush mash should result in a high FG, since saccharification did not have time to create much fermentable sugar.

@RM-MN you have done this experiment, have you not? Did your ultra short mashes result in abnormally high FG's?

Brew on

 

[Vale71]

Hydrolysis water is still coming from the mash, so mass being equal means unless volume is also reduced byt 3.5-4.0% the change in gravity will be smaller than that or possibly even zero if volume is unchanged. Besides that any method relying on changing gravity or even refraction index (the latter does change as hydrolysis proceeds even with invariant gravity) will be totally swamped with noise and be as good as useless. For example, how do you distinguish between gravity increasing by 1 point because more starch/dextrine has come loose from its matrix and finally gone into solution (noise) from the same change occurring simply through glycolysis alone (signal)? You just can't as both scenarios are indistinguishable. In the worst case if enzymes are deactivated prematurely you will eventually observe a stable gravity (or refractometer reading) as no more extract goes into solution and/or is converted, but you will never achieve full conversion no matter how long you wait. Your simple test has only fooled you into believing you have achieved full conversion but you never have.

With the iodine test you directly assess the composition of extract and have a clear pass/fail answer, taking all of 30 seconds at most. Anything else is no different than mashing for a set duration and then hoping everything went well, with no direct confirmation.

 

[doug293cz]

Hydrolysis water is still coming from the mash, so mass being equal means unless volume is also reduced byt 3.5-4.0% the change in gravity will be smaller than that or possibly even zero if volume is unchanged. Besides that any method relying on changing gravity or even refraction index (the latter does change as hydrolysis proceeds even with invariant gravity) will be totally swamped with noise and be as good as useless. For example, how do you distinguish between gravity increasing by 1 point because more starch/dextrine has come loose from its matrix and finally gone into solution (noise) from the same change occurring simply through glycolysis alone (signal)? You just can't as both scenarios are indistinguishable. In the worst case if enzymes are deactivated prematurely you will eventually observe a stable gravity (or refractometer reading) as no more extract goes into solution and/or is converted, but you will never achieve full conversion no matter how long you wait. Your simple test has only fooled you into believing you have achieved full conversion but you never have.

With the iodine test you directly assess the composition of extract and have a clear pass/fail answer, taking all of 30 seconds at most. Anything else is no different than mashing for a set duration and then hoping everything went well, with no direct confirmation.

The formula for Plato is:

°P = 100° * Weight of Extract / Weight of Liquid = 100° * Weight of Extract / (Weight of Extract + Weight of Water)​

The denominator does not change with saccharification, as you state, but the numerator gets larger, so °P goes up.

Monitoring SG during the mash is basically monitoring the increase in dissolved solids. SG will increase until there is no more solid material going into the mash. If as I stated in my previous post, saccharification proceeds much faster than starch dissolution, then once dissolution has completed, saccharification will be completed in just a few minutes after that. And since all the extract is in solution, along with the enzymes, saccharification will continue during lautering and heat up to a boil (until all enzymes are denatured), or continue during heat up to mash out temps (if mashing out prior to lautering.)

The iodine test is only sensitive to amylose chains over a certain length. Once you have no long chain amylose in solution, the iodine test goes negative. That still doesn't mean that saccharification is complete, as there is more molecular weight reduction still to occur.

Many brewers report having trouble getting a negative iodine test if they have grits in their sample, so they carefully exclude grits from their sample, and get the desired negative results. The implications of this is that there is still undissolved starch in the grits, but that the amylose in solution got hydrolyzed below the detection point before gelatinization and dissolution were complete. More evidence that saccharification proceeds faster than gelatinization and dissolution. And if they still have undissolved starch in the grits, they will not have 100% conversion.

Since SG monitoring directly measures completion of dissolution it is a more reliable test for determining when the mash is "almost" complete, and most likely will be complete before the temp is raised enough to complete denaturization.

If your enzymes are denatured prior to the completion of dissolution and saccharification, it doesn't matter what test you use, further saccharification is ended. It's really up the brewer to insure that their grain bill has sufficient diastatic power to complete saccharification, and that they don't denature the enzymes prematurely by mismanaging mash temps.

Brew on

 

[RM-MN]

@RM-MN you have done this experiment, have you not? Did your ultra short mashes result in abnormally high FG's?

The 10 minute and 20 minute mashes seemed to have the same FG as the 30 minute mash. The difference was in the flavor extracted.

Using iodine as an indicator, I found starches converted in about 2 minutes. That is, the iodine on the grain particle would no longer turn blue after about 2 minutes.

 

[CascadesBrewer]

This method will not work. If it did then why would professional brewers still bother with the iodine test?

They do? I have brewed with 3 times at 3 different breweries and we never did an iodine test. I have not done an iodine test with my own homebrew mash in probably 20 years...just let it go for 60 minutes.

The iodine test is that it is only sensitive to amylose chains over a certain length. Once you have no long chain amylose in solution, the iodine test goes negative. That still doesn't mean that saccharification is complete, as there is more molecular weight reduction still to occur.

Yeah...some people with a more in depth knowledge of mash chemistry than me have spoken...but my understanding of an iodine test (and I suspect a gravity reading) is that it does not indicate that amylase activity is complete.

 

[doug293cz]

...

Yeah...some people with a more in depth knowledge of mash chemistry than me have spoken...but my understanding of an iodine test (and I suspect a gravity reading) is that it does not indicate that amylase activity is complete.

You are correct. Neither the iodine test, nor the SG test, tells you when all possible amylase activity has ended. I am not aware of any simple test that does. (You could do some kind of molecular weight sensitive test, but that would be way beyond the capability of all but the largest commercial brewers.) The SG test tells you when no more extract (sugar, starch, proteins, etc.) is entering solution. Depending on how you conduct the iodine test (include or exclude grits from the sample) it can tell you if there is no more "long" chain amylose in solution or in the grits. Evidence points to gelatinization and dissolution being slower than saccharification, so that what limits the mash completion is getting the maximum extract into solution. There should be no difficulty completing saccharification in a few minutes (less than 10) after completion of dissolution, if your grist started with sufficient diastatic power, and the mash was not excessively long (such that the amylase denatured prior to the completion of dissolution.) If you are going to do the iodine test, it should be done with grits included, and the grits smashed just prior to adding iodine, so that you will detect residual starch in the grits. If you leave starch in the grits, there is no way to get 100% conversion.

Brew on

 

[Vale71]

They do? I have brewed with 3 times at 3 different breweries and we never did an iodine test. I have not done an iodine test with my own homebrew mash in probably 20 years...just let it go for 60 minutes.

I'm aware that there are breweries that cut corners at every chance and there are breweries whose beer I really don't care for. Personally I prefer not to follow their example...

I think there is a little misunderstanding that needs to be cleared here. Full conversion does not mean there is no amylase activity any more, but simply that there are no more long-chain polysaccharides in the wort. Long chain is, by tradition if you will, defined through the iodine reaction as to mean >9 glucose units. Of course you can still break down those <=9 glucose units polysaccharides, but it's your choice depending on the attenuation you whish to achieve in your beer, so a stylistic choice if you will.

As for starch being still present in the grits, that does not mean you have not achieved full conversion as long as the starch stays there. The goal is to have no starch in the beer and to achieve that it is sufficient to have no starch in the wort. Any unconverted starch in the grits will however affect efficiency.

 

[hottpeper13]

My first allgrain brew day was eye opening. I asked about the iodine teat and my buddy said just look at the clarity of the wort,when you can see the grain bed it's done. I've never done one and prowlley never will. My mashes last 120 min from start to flame on, mostly step mashing, and my lagers finish between 1.008 and 1.012,and crystal clear.