Mill speed/husk shredding/efficiency/astringency discussion

[TheMadKing]

Hey All,

I just got into a debate on the Brulosophy facebook page. I don't know if anyone has definitively tested this so I thought I would start a thread on it.

Has anyone investigated the impact of milling speed on grain husk shredding, and determined whether this has a real effect on lautering efficiency or increases the risk of tannin extraction?

To me, it makes sense that shredded husks can impact lautering efficiency in a 3-vessel system but are inconsequential in BIAB.

I also am skeptical of the tannin extraction claims, but if increased surface area can increase sugar extraction from grain, it's entirely possible that they can increase the tannin extraction risk.

I would love to hear from someone who has actually tested this experimentally, as well as theory discussions.

 

[dmtaylor]

I don't know about milling speed, but I can tell you from experience that even when crushing the grains dang near to flour, you won't extract tannins unless your mash pH is way high (like >5.8). Keep pH down towards the desirable 5.2-5.5, and the beer will turn out just fine, no astringency.

 

[TheMadKing]

I don't know about milling speed, but I can tell you from experience that even when crushing the grains dang near to flour, you won't extract tannins unless your mash pH is way high (like >5.8). Keep pH down towards the desirable 5.2-5.5, and the beer will turn out just fine, no astringency.

That is the assumption I have always had as well, and I keep my gap setting as small as it can go and mill at full speed with my drill.

I just had a brewer that I highly respect for his expertise tell me that he has had astringency show up in his beer due to husk shredding. This is a person who's opinion on brewing I would never take lightly (PhD in geology, BJCP master judge, been making beer for 40+ years). So when he say's he's gotten astringency from it, I won't just dismiss it without testing it.

 

[TheMadKing]

Well I guess this is either a dead horse, or there isn't much info out there?

 

[techbrau]

For what it's worth, the textbooks used by the German brewing universities like Narziss and Kunze all caution against shredding the husk because it releases a larger quantity of undesirable enzymes like LOX and PPO which can then work to create increased quantities of staling compounds, which can also be astringent. They go through significant lengths to keep the husk intact via processes like steam conditioning, and sometimes even strip away the worst offending parts of the husk like where the arcospire attaches because they contain the greatest concentration of the bad enzymes. But most American craft breweries and homebrewers pay little to no attention to any of that.

It all boils down to whether you find German lagers to be less astringent in some sense than American craft beer. If no, don't worry about it. If yes, then maybe pick up a copy of Kunze's book and see what more he has to say.

 

[petrolSpice]

Quite a few of the BIAB folk are turning their grains into essentially flour with super tight mills or even using a blender or food processor. If tannin extraction was an issue I don't think this would be as common as it is. Although I can't speak from experience.

 

[doug293cz]

...

I also am skeptical of the tannin extraction claims, but if increased surface area can increase sugar extraction from grain, it's entirely possible that they can increase the tannin extraction risk.

I would love to hear from someone who has actually tested this experimentally, as well as theory discussions.

The big difference between the kinetics of grain extraction behavior and husk extraction behavior, is that grains have a much lower surface area to volume ratio than husks, and that the minimum dimension of husks (their thickness) is very much smaller than the minimum dimension of grain kernels. The rate of diffusion controlled processes, like gelatinization and tannin extraction, is strongly dependent on the minimum dimension (smaller dimensions increase rates), and surface area to volume ratio (larger ratios increase rates.) Unless you turn the husks into powder, shredding them does not have much of an affect on their minimum dimension, so doesn't have a huge effect on extraction rates. It also doesn't increase the surface area to volume ratio that much. Grain kernels are different, since the difference between minimum dimension and maximum dimension is much smaller than husks (aspect ratio is smaller.) Crushing the grain does significantly increase the surface area to volume ratio, and a fine crush will also significantly decrease the minimum dimension, both of which will increase the gelatinization rate (and thus saccharification rate.)

Brew on

 

[TheMadKing]

The big difference between the kinetics of grain extraction behavior and husk extraction behavior, it that grains have a much lower surface area to volume ratio than husks, and that the minimum dimension of husks (their thickness) is very much smaller than the minimum dimension of grain kernels. The rate of diffusion controlled processes, like gelatinization and tannin extraction, is strongly dependent on the minimum dimension (smaller dimensions increase rates), and surface area to volume ratio (larger ratios increase rates.) Unless you turn the husks into powder, shredding them does not have much of an affect on their minimum dimension, so doesn't have a huge effect on extraction rates. It also doesn't increase the surface area to volume ratio that much. Grain kernels are different, since the difference between minimum dimension and maximum dimension is much smaller than husks (aspect ratio is smaller.) Crushing the grain does significantly increase the surface area to volume ratio, and a fine crush will also significantly decrease the minimum dimension, both of which will increase the gelatinization rate (and thus saccharification rate.)

Brew on

The surface area argument makes perfect sense and can be easily demonstrated by calculating the surface area of two cylinders with different radii.

The only slight argument I might make is: I think you are making an assumption about the amount of effect that husk particle size has on extraction, or lautering efficiency. You are assuming that tannin extraction is diffusion controlled and not reaction rate dependent to a degree that might impact the results.

I fully agree with you in theory that it SHOUDN'T matter, but I think an experimental demonstration is always good practice to make sure there isn't some unanticipated mechanism taking place. Always glad to get your input Doug, thanks!

 

[TheMadKing]

Quite a few of the BIAB folk are turning their grains into essentially flour with super tight mills or even using a blender or food processor. If tannin extraction was an issue I don't think this would be as common as it is. Although I can't speak from experience.

Agreed, I'm one of them. It had never even occurred to me that the rate of milling could impact my beer, and it seems there's little research done on the subject, despite the fact that it is debated fairly often.

 

[TheMadKing]

For what it's worth, the textbooks used by the German brewing universities like Narziss and Kunze all caution against shredding the husk because it releases a larger quantity of undesirable enzymes like LOX and PPO which can then work to create increased quantities of staling compounds, which can also be astringent. They go through significant lengths to keep the husk intact via processes like steam conditioning, and sometimes even strip away the worst offending parts of the husk like where the arcospire attaches because they contain the greatest concentration of the bad enzymes. But most American craft breweries and homebrewers pay little to no attention to any of that.

It all boils down to whether you find German lagers to be less astringent in some sense than American craft beer. If no, don't worry about it. If yes, then maybe pick up a copy of Kunze's book and see what more he has to say.

Good info, I've never heard that before!

 

[doug293cz]

...

The only slight argument I might make is: I think you are making an assumption about the amount of effect that husk particle size has on extraction, or lautering efficiency. You are assuming that tannin extraction is diffusion controlled and not reaction rate dependent to a degree that might impact the results.

I fully agree with you in theory that it SHOUDN'T matter, but I think an experimental demonstration is always good practice to make sure there isn't some unanticipated mechanism taking place. Always glad to get your input Doug, thanks!

If in fact tannin (or silicate for that matter) extraction is reaction rate dependent, rather than diffusion rate dependent, then minimum dimension and surface area to volume ratio are even less important to rate or degree of extraction, making the question of the effect of hull shredding even less interesting.

I agree that experimental verification of theory is critical, even if it is not easy.

I made no comment about affect on lautering in my previous post. I am currently of the belief that more intact husks will promote better flow thru the grain bed, which would enhance lautering, especially for traditional MLT's/lauter tuns. Of course larger grain grits, and fewer fines in the mix, will also enhance flow thru the grain bed.

Brew on

 

[TheMadKing]

If in fact tannin (or silicate for that matter) extraction is reaction rate dependent, rather than diffusion rate dependent, then minimum dimension and surface area to volume ratio are even less important to rate or degree of extraction, making the question of the effect of hull shredding even less interesting.

I agree that experimental verification of theory is critical, even if it is not easy.

I made no comment about affect on lautering in my previous post. I am currently of the belief that more intact husks will promote better flow thru the grain bed, which would enhance lautering, especially for traditional MLT's/lauter tuns. Of course larger grain grits, and fewer fines in the mix, will also enhance flow thru the grain bed.

Brew on

Agreed on your first and second paragraph.

In regards to lautering efficiency, that is where my reasoning leads me as well. Experimentally, one could argue that adding rice hulls is essentially replacing or augmenting large grain husks which demonstrates the effectiveness of in-tact husks at improving lautering.

I do wonder if it has an effect on BIAB lautering efficiency though. It seems that it should not, since the bag is replacing the husks as a mechanical filter and the rate of wort drain from the grain bed should not affect its dissolved sugar content.

 

[doug293cz]

Agreed on your first and second paragraph.

In regards to lautering efficiency, that is where my reasoning leads me as well. Experimentally, one could argue that adding rice hulls is essentially replacing or augmenting large grain husks which demonstrates the effectiveness of in-tact husks at improving lautering.

I do wonder if it has an effect on BIAB lautering efficiency though. It seems that it should not, since the bag is replacing the husks as a mechanical filter and the rate of wort drain from the grain bed should not affect its dissolved sugar content.

It's pretty easy to run an experiment on whether or not rice hulls will affect BIAB lautering efficiency. I might just run such an experiment. Only downside is that I will have to drink two batches of the same beer, one after the other.

Edit: On second thought, I could use different hops/yeast and have different beers with the same grain bill.

Brew on

 

[TheMadKing]

It's pretty easy to run an experiment on whether or not rice hulls will affect BIAB lautering efficiency. I might just run such an experiment. Only downside is that I will have to drink two batches of the same beer, one after the other.

Brew on

You could always split a smaller batch, and recombine them after measuring the pre-boil gravities.

Or I'm sure that donating beer is frowned upon in very few places

 

[doug293cz]

You could always split a smaller batch, and recombine them after measuring the pre-boil gravities.

Or I'm sure that donating beer is frowned upon in very few places

SG's are potentially affected by differences in conversion efficiency between batches. So, I was thinking of measuring volumes after a constant drain time, and then again after a controlled squeeze. Figuring out how to do a consistent squeeze will be the tricky part. Here, I am thinking let a bucket full of water sit on the bag, held in a colander, for a fixed amount of time.

Brew on

 

[TheMadKing]

SG's are potentially affected by differences in conversion efficiency between batches. So, I was thinking of measuring volumes after a constant drain time, and then again after a controlled squeeze. Figuring out how to do a consistent squeeze will be the tricky part. Here, I am thinking let a bucket full of water sit on the bag, held in a colander, for a fixed amount of time.

Brew on

You could also homogenize the grain by milling it all together, and then separating it post milling to help reduce differences in conversion rates. Rest temperature is also a difficult variable to control accurately unless you have a HERMS or RIMS system.

 

[Totally]

It's pretty easy to run an experiment on whether or not rice hulls will affect BIAB lautering efficiency.

Another experiment here that I would like to see would be grain conditioning since it should allow for a balance between a nice fine crush while leaving the husks more intact.

Is lautering efficiency the only reason people condition grains or do astringency issues come into play as well?

 

[TheMadKing]

Another experiment here that I would like to see would be grain conditioning since it should allow for a balance between a nice fine crush while leaving the husks more intact.

Is lautering efficiency the only reason people condition grains or do astringency issues come into play as well?

I know virtually nothing about grain conditioning, so I would certainly be curious to learn more about it as well.

 

[doug293cz]

You could also homogenize the grain by milling it all together, and then separating it post milling to help reduce differences in conversion rates. Rest temperature is also a difficult variable to control accurately unless you have a HERMS or RIMS system.

Homogenizing the milled grain is easier said than done (this is actually something I studied in school.) The course and fine fractions tend to stratify in a container, and if different grains are involved, getting the ratio the same in both splits is also difficult. They do make a special device for making splits to mitigate these issues, but it's not something I want to spend money or time (to DIY) on. I'm pretty good at getting consistent mash temps, and I mill my own grain, so I think I can control those variables. Also, a difference in conversion efficiency will affect SG more than it will affect wort viscosity (and thus flow thru the grain mass), which is why I would focus on lautered volumes.

Brew on

 

[TheMadKing]

Homogenizing the milled grain is easier said than done (this is actually something I studied in school.) The course and fine fractions tend to stratify in a container, and if different grains are involved, getting the ratio the same in both splits is also difficult. They do make a special device for making splits to mitigate these issues, but it's not something I want to spend money or time (to DIY) on. I'm pretty good at getting consistent mash temps, and I mill my own grain, so I think I can control those variables. Also, a difference in conversion efficiency will affect SG more than it will affect wort viscosity (and thus flow thru the grain mass), which is why I would focus on lautered volumes.



Brew on

Duh, now that you say that I, I did granular sample homogenization of soils for XRD once. I forgot all about that stupid centrifuge splitter.

I look forward to hearing your results. I'm debating experimenting with drill speeds for an upcoming dopplebock brew that I could easily split. Without an accurate way to measure my rpm's the data would all be relative, and efficiency results would be hard to link to that variable.

 

[The_Bishop]

I BIABasket, with a recirculating rig and a stainless mesh basket. I have found that with a slightly larger crush, (resulting in a better husk) I have no recirculation issues and can recirculate at 100% flow via a chugger pump. I have also discovered that the grain drains faster, with less to be gained via 'squeezing' (I use a 24" whisk that I use for grain-in in a 'potato masher' fashion.)

To me,there's a definite benefit to a more intact husk. FWIW, I use a high-torque low speed drill at roughly 200rpm when I crush.

 

[TheMadKing]

I BIABasket, with a recirculating rig and a stainless mesh basket. I have found that with a slightly larger crush, (resulting in a better husk) I have no recirculation issues and can recirculate at 100% flow via a chugger pump. I have also discovered that the grain drains faster, with less to be gained via 'squeezing' (I use a 24" whisk that I use for grain-in in a 'potato masher' fashion.)

To me,there's a definite benefit to a more intact husk. FWIW, I use a high-torque low speed drill at roughly 200rpm when I crush.

Good info, and that should definitely be shared as a solution to slow recirculation issues. I've seen a few threads related to that problem recently.

I expect that you've never noticed a flavor or gravity impact that you have attributed to your mill speed though?

 

[doug293cz]

I BIABasket, with a recirculating rig and a stainless mesh basket. I have found that with a slightly larger crush, (resulting in a better husk) I have no recirculation issues and can recirculate at 100% flow via a chugger pump. I have also discovered that the grain drains faster, with less to be gained via 'squeezing' (I use a 24" whisk that I use for grain-in in a 'potato masher' fashion.)

To me,there's a definite benefit to a more intact husk. FWIW, I use a high-torque low speed drill at roughly 200rpm when I crush.

How did you determine that the better flow was due to better husk integrity, rather than better flow due to larger grits and less fines in the grist, or a combination of both?

Brew on

 

[bleme]

I know virtually nothing about grain conditioning, so I would certainly be curious to learn more about it as well.

I only conditioned one batch. Unfortunately, I chose a Barleywine with 20 pounds of grain to experiment with. The conditioned grain was too much for my drill to handle so I had to switch in the hand crank and do all 20 pounds the hard way. Bloodied my knuckles, but it was a beautiful, fluffy crush. Not nice enough for me to do it again though...

 

[The_Bishop]

How did you determine that the better flow was due to better husk integrity, rather than better flow due to larger grits and less fines in the grist, or a combination of both?

Brew on

It took three brews. With the same mill gap and no conditioning, I had flow issues. With conditioning and no gap change, no flow issues and draining seemed quicker. This was with the same two roller mill and no change in gap.

Third brew was with my new three roller mill. Same second gap as the two roller mill, but with the benefit of the primary crush and a slower speed on the drill, the husks remained largely intact and the starch was almost completely separated from the husk. This flowed as well as the conditioned milling without needing the added step.

 

[doug293cz]

It took three brews. With the same mill gap and no conditioning, I had flow issues. With conditioning and no gap change, no flow issues and draining seemed quicker. This was with the same two roller mill and no change in gap.

Third brew was with my new three roller mill. Same second gap as the two roller mill, but with the benefit of the primary crush and a slower speed on the drill, the husks remained largely intact and the starch was almost completely separated from the husk. This flowed as well as the conditioned milling without needing the added step.

That makes sense. In your previous post, you said "I have found that with a slightly larger crush", which implied that the gap had been changed.

Brew on

 

[Anyhowe]

Just did my first grind with the Ale Works direct drive mill at 180 rpm. Although I don't have an a/b test, the consistency of the grind and the performance of the mash was most excellent compared to my drill.

 

[The_Bishop]

That makes sense. In your previous post, you said "I have found that with a slightly larger crush", which implied that the gap had been changed.

Brew on

Yeah, my apologies on that. Was too tired to be posting anything coherent.

 

[dyqik]

I don't know about milling speed, but I can tell you from experience that even when crushing the grains dang near to flour, you won't extract tannins unless your mash pH is way high (like >5.8). Keep pH down towards the desirable 5.2-5.5, and the beer will turn out just fine, no astringency.

If you sparge, I believe it's also important to acidify the sparge water so that you don't raise the pH during the sparging process and extract tannins then as well. I think this is more of an issue for fly sparging than batch sparging.

 

[dmtaylor]

If you sparge, I believe it's also important to acidify the sparge water so that you don't raise the pH during the sparging process and extract tannins then as well. I think this is more of an issue for fly sparging than batch sparging.

Valid point. As a batch sparger, I tend to forget about this.