Mash Conversion Experiment

I ran a little experiment today to see how long mash conversion takes. This has been discussed many, many times on other threads so I thought I'd do my own experiment and post the results.

9.5lbs of grain -- Thin mash 2qt/lb -- 60min total -- Strike water @162F to reach a starting mash temp of 151F -- I took gravity readings using a refractometer

Minutes ------- Gravity
2.5 --- 1.036
5 --- 1.040
10 --- 1.043
15 --- 1.049
20 --- 1.052
25 --- 1.054
30 --- 1.057
45 --- 1.063 (possible bad stir?)
60 --- 1.061

* Lost 5-8F over hour due to stirring every 5-15min

Sparge: 3.5gal @ 195F to reach 168F
0 --- 1.016
10 --- 1.019

Combined Runnings: 7.5 gal
1.040

So, I had an odd reading at 45min that then decreased at 60min. I have to assume I didn't give a good enough stir at 45min. My overall findings here are pretty clear though. Full conversion may have been done as early as 45min possibly even a bit earlier, but gravity was still rising after 30min.

I do plan on running this same experiment again but with a barley wine where I'll be using a much thicker mash of around 1.25qt/lb. Hoping to brew that beer and have results in either 2 or 3 weeks.

Can you comment on how fine your crush was? Typical 3-vessel system crush or BIAB dust-crush?

BTW, thanks for sharing your results!

IIRC, time for conversion is partially dependent on crush.

finer crush means more surface area contact with water = shorter conversion time

Sorry, meant to address that. Yes, I BIAB dust-crush... pretty fine. Definitely finer than the average crush where the kernel is simply cracked open.

For scientific purposes... (cough cough)... I'll be trying this experiment out a few more times with different mash thicknesses. In a few weeks I'll brew a barley wine with a thickness of about 1qt/lb. Then I'll try another beer with a thickness of 1.5qt/lb. Then I'll go back and rerun this same experiment as today at 2qt/lb. Maybe I'll throw in another full volume BIAB mash just to see what I can learn. I prefer to mash thin, but still sparge to get those extra gravity points. I've already experimented with BIAB sparge, BIAB full volume no sparge, etc and prefer BIAB thinner mash w/sparge. This gets me around 80-85% efficiency for average sized grain bills. I've noticed a significant drop in efficiency with full volume mashing no sparge, but I will give it another try to study conversion times.

I look forward to your results from your testing. It looks like a refractometer purchase is in your near future . As far as OG testing goes, I have found the refractometer to be the most reliable method because it doesn't register starch gravity points (like a hydrometer) nor does it stop registering change in gravity at a certain point (like the iodine test). Additionally, my personal comparative logging with a refractometer vs hydrometer for FG has shown the discrepancy to be generally minimal but would recommend anyone using one for FG to do their own record keeping to decide how useful it is for FG because I think equipment plays a big role in this.

OP, stpug... says he took readings with refractometer

GrogNerd said:

OP, stpug... says he took readings with refractometer

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Yeah, I know. I guess my last post didn't make that obvious. Sorry about that.

I don't totally understand. Gravity and conversion aren't the same, are they? Couldn't you get 60 points of gravity but not converted? All starch waiting to convert?

Gravity comes from starch converting to sugar. And a refractometer shows the amount of converted sugar in liquid. In this case wort.

ericbw said:

I don't totally understand. Gravity and conversion aren't the same, are they? Couldn't you get 60 points of gravity but not converted? All starch waiting to convert?

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The following post is from a NON-scientist (me )

You CAN get gravity points from starch alone (unconverted starches), you are correct. Additionally, a hydrometer will register starch as gravity because specific gravity is a measure of the density of a solution as compared to a reference solution (i.e. water) and the starch changes that (as does sugar). Interestingly, a refractometer doesn't register starches as brix (i.e. sugar content), therefore is the instrument of choice for this sort of testing, IMO.

Specific gravity and "conversion" are not the same thing. Specific gravity is what I mentioned above and "conversion" is the process of enzymes breaking down starches into smaller-chain sugars.

You CAN get 60 specific gravity points from starch alone using a hydrometer. Get your self some water and start adding flour/cornstarch/clay and check the gravity. I don't know how much flour/cornstarch would be needed but with enough you'll get there, and you can be certain there is nothing sweet about that mixture . Thus, you can have gravity without conversion.

The data that you came up with is appreciated. Here are a few things that you might want to consider. Along with crush as the other brewer mentioned, mash thickness, temp and pH are important parts of the conversion cycle. At 151F beta range, with a thin mash, beta denatures very quickly. The product will have quick conversion and high attenuation with a thin mash at 151F. Starch gelatinizes at 149F, optimum pH for Beta is different than Alpha, starch bursts at 168F. A thicker mash preserves enzymes. When you do the 1qt/lb test you will need to pay attention to the viscosity number on the grain data sheet. The mash can jell up, being full of large a and or b limit dextrines. This becomes a problem when iodine is used to gauge conversion. A mash is started thick in certain brewing methods. Usually, in those processes, mash is thinned down throughout the process or boiled and different temp rests are employed to utilize certain enzymes that reduce viscosity.

VladOfTrub said:

The data that you came up with is appreciated. Here are a few things that you might want to consider. Along with crush as the other brewer mentioned, mash thickness, temp and pH are important parts of the conversion cycle. At 151F beta range, with a thin mash, beta denatures very quickly. The product will have quick conversion and high attenuation with a thin mash at 151F. Starch gelatinizes at 149F, optimum pH for Beta is different than Alpha, starch bursts at 168F. A thicker mash preserves enzymes. When you do the 1qt/lb test you will need to pay attention to the viscosity number on the grain data sheet. The mash can jell up, being full of large a and or b limit dextrines. This becomes a problem when iodine is used to gauge conversion. A mash is started thick in certain brewing methods. Usually, in those processes, mash is thinned down throughout the process or boiled and different temp rests are employed to utilize certain enzymes that reduce viscosity.

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Not sure what you mean by this? And I'm not sure what point you are trying to get across in your last few sentences. Sounds like you're talking about decoction, but I'm not sure how that pertains to the topic.

What kind of malt did you use? I've heard highly modified North American malts can convert much quicker than Euro malts?

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Just want to add that in the past I fooled with all sorts of mash thickness ratios and there were absolutely no taste, efficiency, or FG differences BUT I kept the time constant (60 minutes).

listening to a Brewing Network podcast and Tasty McDole was saying he mashes in with 9 gallons, regardless of amount of grain, for an 11-gallon batch

so, his mash for lower-gravity batches is thin, for bigger beers it is thicker

GrogNerd said:

listening to a Brewing Network podcast and Tasty McDole was saying he mashes in with 9 gallons, regardless of amount of grain, for an 11-gallon batch

so, his mash for lower-gravity batches is thin, for bigger beers it is thicker

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That's generally what I do too. I usually mash with about 5 gallons which is on the thinner side (1.75 - 2qt/lb). I usually like my beers to be on the drier side (not all but usually) and a thinner mash at lower temps helps a good deal with conversion and attenuation. But with bigger beers I don't usually up the water that much. I just adjust for a thicker mash.

For these experiments I obviously have to step away from my normal practices and mash thicker and thinner to see what I get.

dobe12 said:

That's generally what I do too. I usually mash with about 5 gallons which is on the thinner side (1.75 - 2qt/lb). I usually like my beers to be on the drier side (not all but usually) and a thinner mash at lower temps helps a good deal with conversion and attenuation. But with bigger beers I don't usually up the water that much. I just adjust for a thicker mash.

For these experiments I obviously have to step away from my normal practices and mash thicker and thinner to see what I get.

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I've read that mash times affect attenuation, not the thickness of the mash. If you want a more attenuated beer, mash longer.

Your experiment would have been better if you had kept mashing until your SG had stopped changing so we could have gotten an idea of when time doesn't affect the mash SG anymore.

2 more tests were run to add to these mash time experiments. The first by me this past weekend. I don't have my numbers in front of me, but in a nutshell, 1.5qt/lb. A good bit of conversion happened during the first few minutes, but continued for about 45min.

A fellow brew club member also ran this experiment on his system (completely different than mine) and got similar results. This was for a 10gal mash on a HERMS system using 1.4qt/lb and here's what he got.

05 - 1.040
10 - 1.048
15 - 1.053
20 - 1.056
25 - 1.058
30 - 1.060
40 - 1.063
50 - 1.065
60 - 1.066

I plan on running a few more tests with more dramatic scenarios like 1qt/lb thick large mash. I'm also going to do a full volume, BIAB, no sparge mash to see what I get. I am assuming the results will be similar, but we'll see.

As of now, I fully believe that a large portion of conversion happens within the first few minutes (40-60% or more), but conversion DOES continue for roughly 30-45min if not longer. As of now, I won't be shortening my mashes and brew days. And I don't believe anyone who says they are getting full conversion in 5-10minutes or less. A lot of conversion, yes. Full, no way.

Thanks for posting results, and looking forward to some of the future tests - especially the BIAB full volume, no sparge. That's what I've been doing since starting BIAB, and I'm interested to see how it compares to some of the other methods.

No problem at all. I love trying out things like this.

About a year ago I did a few full volume, no sparge, BIAB beers, but noticed a considerable loss in efficiency. But since then I've added a larger mash/brew kettle, larger grain sack, and started milling my own grain. I'd love to go back to no sparge just to save some time and simplify my brew day. Even if my efficiency drops a little bit, I'd be ok with it.

I'll continue to post results from other tests.

I've been getting 80-82% pretty consistently for the past 6 batches (only been doing BIAB since the beginning of the year, started around 75% and made some small tweaks along the way) by crushing as fine as I can with my Cereal Killer and doing full volume 60-minute mashes with anywhere between 8 and 12 lbs of grain. I'm definitely not opposed to making more changes to shorten my mash time and/or increase efficiency though.

Very nice. Do you plan on any extended tests? Like for example... Mash for 2 hours at 148* then a short 10 minute rest at 158*.

Thanks for update. TIMELY. No time to brew this weekend but did a TON of digging on the matter and cranking out liter to kg to qt to lb conversions.

Kai has alot of good stuff and his work is full of excellent citations from a variety of sources. There are some conflicting points, but the gist is that a thick mash converts faster but is less efficient and a thinner mash vice versa. From what I gleaned, the point of diminishing returns is 1.2qts per lb (Briggs). That's frigging thick. Curious how an old school british 1qt:1lb mash and/or 1.2:1 would test out. Personally, I like the thinner mash since it easier to measure and stir but would be glad to change to thicker if we can prove it works. Does a refractometer cut the mustard? I have a love/hate relationship with pH meters...

A side note, I am a big advocate of acidifying sparge and this will especially hold true if you do a thick mash since the volume of the sparge will be greatly increased...

I have a saison on deck and will prolly just go ahead and do 1.2:1 for 60m.

grathan said:

Very nice. Do you plan on any extended tests? Like for example... Mash for 2 hours at 148* then a short 10 minute rest at 158*.

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Haven't thought about that sort of test yet, but possibly in the future. If you give it a shot, check back in with your results.

My next batch is a barley wine that I plan to do a 90min, thick mash. I'll report back.

grathan said:

Very nice. Do you plan on any extended tests? Like for example... Mash for 2 hours at 148* then a short 10 minute rest at 158*.

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I'd be happy with just extending the test to 90' to prove it is a waste of time.

I meant to ask to confirm this before, but is the main objective to the thread to shorten the mash/brew day or max efficiency? My goal is the former

zwiller said:

Thanks for update. TIMELY. No time to brew this weekend but did a TON of digging on the matter and cranking out liter to kg to qt to lb conversions.

Kai has alot of good stuff and his work is full of excellent citations from a variety of sources. There are some conflicting points, but the gist is that a thick mash converts faster but is less efficient and a thinner mash vice versa. From what I gleaned, the point of diminishing returns is 1.2qts per lb (Briggs). That's frigging thick. Curious how an old school british 1qt:1lb mash and/or 1.2:1 would test out. Personally, I like the thinner mash since it easier to measure and stir but would be glad to change to thicker if we can prove it works. Does a refractometer cut the mustard? I have a love/hate relationship with pH meters...

A side note, I am a big advocate of acidifying sparge and this will especially hold true if you do a thick mash since the volume of the sparge will be greatly increased...

I have a saison on deck and will prolly just go ahead and do 1.2:1 for 60m.

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I've read the same thing about thicker mash converting quicker, but not as fully. While a thinner mash is slower, but will convert fuller. So far, I see no evidence of that, but have only 3 tests so far. The next will be big, thick mash around 1-1.25qt/lb. And will then do another full volume mash around 3.25-3.5qt/lb. These should have very conflicting results if the above is true. We'll see.

zwiller said:

I'd be happy with just extending the test to 90' to prove it is a waste of time.

I meant to ask to confirm this before, but is the main objective to the thread to shorten the mash/brew day or max efficiency? My goal is the former

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Well it started because a HBT member claims to get full conversion in 5-10min or less. I didn't believe it at all. History plus these test results prove that not to be true. But for me, it then turned into "hey, wonder if I can shorten my brew day". I've yet to see any evidence that would lead me to shorten my mash by 30min or more. Sure, a lot of conversion is complete in the first 30min, but things are still going on after that point. I personally don't feel the need to lose efficiency just to cut 15min from my brew day, which is the max I'd be willing to cut my mash times from my evidence that conversion is still happening up to and past 30-45min.

zwiller said:

I'd be happy with just extending the test to 90' to prove it is a waste of time.

I meant to ask to confirm this before, but is the main objective to the thread to shorten the mash/brew day or max efficiency? My goal is the former

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If I'm not mistaken, the goal is to determine how long it takes for a mash to fully convert the starches to sugars in various circumstances. The practical applications (shortening brew day or improving efficiency) would be secondary to the actual data.

Edit: NM, dobe had faster fingers than I did.

boydster said:

If I'm not mistaken, the goal is to determine how long it takes for a mash to fully convert the starches to sugars in various circumstances. The practical applications (shortening brew day or improving efficiency) would be secondary to the actual data.

Edit: NM, dobe had faster fingers than I did.

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I guess the tests started as "No way, I don't believe this guy", but grew to encompass all of the goals listed. Some are just secondary.

Up until recently, I always did 90 minute mashes, as I started out that way. Recently, I thought I would check to see if my conversion was complete at 60 minutes using iodine. None changed color. If my efficiency has dropped, I haven't noticed it. Possibly my checking the S.G. to see if there is any sugar left in the grain, and if so, I will sparge with another gallon, and see if I am at 1.015 or so, and stop sparging. Off to the BK....

Thanks for the additional test. Did you have any pics of your crush? That seems to be the claim that RM-MN makes for how he converts so quickly, I don't remember any comment on his mash thickness. On a side note, I'll be brewing for a friends wedding. Something around 20 gallons in the next 3 months, so if I can get a hold of a refractometer I'll join the party with various crushes from 5 to 60 minutes.

I've done 3 batches with 30 minute mashes so far and it is a game changer for me. Brew time is precious with a young family. I am willing to sacrifice some efficiency to save time... The resulting beers are as good as my 60 minute mashes, but I have a few issues to tweak. A slight efficiency loss, clarity, and slightly higher FG. I wonder if a thicker mash might fix them. Efficiency loss is cool with me, since I am now in high 70's from mid 80's but I think I could do better. Clarity just requires more cold crashing time. The higher FG could also be attributed to using a new yeast strain. In any event, the 2nd 30 minute mash beer is a porter and is the best beer I have EVER made but this is mainly attributed to a experienced brewer suggesting new yeast strain for me and not the fact it was a 30 minute mash. I am long overdue to try a single batch sparge again to see if I can whittle out another 15 minutes. Last time I did it the efficiency got hit hard. The no sparge scares me.

Might join the refractometer party too if it's not too finicky.

pricelessbrewing said:

Thanks for the additional test. Did you have any pics of your crush? That seems to be the claim that RM-MN makes for how he converts so quickly, I don't remember any comment on his mash thickness. On a side note, I'll be brewing for a friends wedding. Something around 20 gallons in the next 3 months, so if I can get a hold of a refractometer I'll join the party with various crushes from 5 to 60 minutes.

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My crush is pretty fine. Much finer than what I got from my LHBS in the past. Since I BIAB and crush myself, I like the added efficiency from a finer crush. I'm sure I could crush even finer, but really don't know how much if would help with efficiency. The husks are all open and there is a good bit of powder.

In the end, the enzymes need time to do their job. They seem to make very quick work of a good portion of the starches, converting to sugar, but they continue to convert for 30-45min and longer. At least that's what my results are showing.

Sure if you don't mind a slight loss in efficiency (and it would only be a few points) you could mash for 30min. I would still prefer to get those extra points and let it sit for a full hour.

zwiller said:

...The resulting beers are as good as my 60 minute mashes, but I have a few issues to tweak. A slight efficiency loss, clarity, and slightly higher FG. ...

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Just a side note that all three of those issues can be directly related to incomplete conversion (i.e. unconverted starch) which could potentially be your culprit. Loss of sugar from wort due to unconverted starches (efficiency loss), starch haze (clarity), unfermentable starches in beer (higher FG using hydrometer).

dobe12 said:

My crush is pretty fine. Much finer than what I got from my LHBS in the past. Since I BIAB and crush myself, I like the added efficiency from a finer crush. I'm sure I could crush even finer, but really don't know how much if would help with efficiency. The husks are all open and there is a good bit of powder.

In the end, the enzymes need time to do their job. They seem to make very quick work of a good portion of the starches, converting to sugar, but they continue to convert for 30-45min and longer. At least that's what my results are showing.

Sure if you don't mind a slight loss in efficiency (and it would only be a few points) you could mash for 30min. I would still prefer to get those extra points and let it sit for a full hour.

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Try crushing finer. Briess Malting has a graph that shows almost the same conversion regardless of the quality of the crush and even without crushing but they didn't say how long it took to get that conversion. I suspect that the uncrushed grain took days to convert fully.

RM-MN said:

Try crushing finer. Briess Malting has a graph that shows almost the same conversion regardless of the quality of the crush and even without crushing but they didn't say how long it took to get that conversion. I suspect that the uncrushed grain took days to convert fully.

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Like I said, my crush is pretty fine. Any finer and I'd be making flour, which I have no intention of doing. There's already a good bit of powder now.

With all due respect RM-MN, I think you may need to admit that full conversion does take longer than 5min like you've claimed. I'm doing my research from one end showing that it takes 30-45min for full conversion, if not longer. If you claim to get full conversion in 5-10min, how about you take a few gravity readings with a refractometer next time you brew and share your results?

stpug said:

Just a side note that all three of those issues can be directly related to incomplete conversion (i.e. unconverted starch) which could potentially be your culprit. Loss of sugar from wort due to unconverted starches (efficiency loss), starch haze (clarity), unfermentable starches in beer (higher FG using hydrometer).

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That's what I am hoping for!

Got curious and measured my mill's gap and it's at least .040" now. Gonna fool with it and tighten it see where it takes me. After some googling I learned that pro brewers run solder through and measure it with caliper. I like that, too much variance with the feeler gauges.

OP, I think some of this talk was in one of my threads. My issue with your experiment is your use of a refractometer and the direct comparison to conversion.

You are measuring wort dissolved organic solids with the refractometer, which will certainly include protein and lipids (albeit in low levels), in addition to sugar. These are additional variables that make your measurement less accurate. Of course, these components exist when measuring brix during any other brew day, but the correlation to conversion is inaccurate. The concentration of some of these components will also be increasing over time during the mash.

However, the use of an iodine based conversion test will provide a more accurate measurement of the actual process of conversion that is occurring over time, instead of including a number of assumptions based on brix. My guess is that actual conversion does occur pretty quick.

Kaiser's experiments suggest mash thickness has a greater impact on conversion efficiency than all the other variables (pH, time, crush). The problem with most of these other experiments is that they are not directly translatable to general brewing practices; they only hold true for the specific experiment, are difficult to replicate, and contain many assumptions and uncontrolled variables.

That said, I very much appreciate your idea. The more people we get to carefully and repeatedly measure aspects of their brew day, the more interesting and appropriate the discussions become.