Author: Jake Huolihan

Easily overlooked by those of less nerdy and/or obsessive persuasion, grain crush is believed by many to play various roles in the brewing process. Like most homebrewers, I started out by purchasing grains on a batch-by-batch basis from a local shop where they were milled for me, leaving me with no control over the crush. Looking to save some dough, I started buying ingredients in bulk and milling my own grains, which is really when grain crush became something I thought about. My mill came preset with a 0.045″ gap that I left alone per the manufacturer’s suggestion. It worked well and allowed me to achieve predictable, albeit somewhat low, efficiency between batches.

With no pressing reason to change, I became intrigued after hearing that some brewers, particularly those utilizing the brew in a bag method, were experiencing improved extract efficiency by mashing grains milled extremely fine. This made practical sense to me, but based on information I’d previously read and heard suggesting fine milling led to increased tannin extraction, I was curious if the resultant beers ended up with more astringency or perhaps some other unique character. Results from our first xBmt on this variable showed crush size seemed to impact not only efficiency but overall beer character, as tasters were able to reliably distinguish between the samples. Interesting, indeed, but I was left wanting for more, as I don’t brew too many high OG styles, so I decided to replicate it on something a bit more tame.

| PURPOSE |

To evaluate the differences between an American Pale Ale made with either a coarse or fine crushed grist that are otherwise treated identically.

| METHODS |

I thought a simple Pale Ale would be a good fit for this variable and doubled the size of a recent batch for The Hop Chronicles for a twofer brew.

Hüllmühle Pale Ale

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 29.4 IBUs 5.6 SRM 1.054 1.012 5.6 % Actuals 1.054 1.008 6.0 % Fermentables Name Amount % Briess Pale Ale Malt 11.25 lbs 95.74 Weyermann Vienna 8 oz 4.26 Hops Name Amount Time Use Form Alpha % Huell Melon 26 g 60 min Boil Pellet 4.5 Huell Melon 31 g 30 min Boil Pellet 4.5 Huell Melon 31 g 5 min Boil Pellet 4.5 Huell Melon 31 g 0 min Boil Pellet 4.5 Huell Melon 30 g 5 days Dry Hop Pellet 4.5 Yeast Name Lab Attenuation Temperature California Ale (WLP001) White Labs 77% 68°F - 73°F Notes Water Profile: Ca 64 | Mg 0 | Na 8 | SO4 75 | Cl 61 | pH 5.4

After determining the amount of yeast each batch would require, I built a single large starter that would later be split between fermentors.

The night before brewing, I readied my equipment, weighed out the grains, and collected two volumetrically equal sets of water that were both adjusted to my preferred profile. Since this variable required separate mashes, I started off the next morning by hitting the flame under one of the kettles, staggering the start of the second batch by 20 minutes.

I milled each set of grains as the strike water was heating. Since I’d been using my mill for awhile without making any adjustments, I figured there was no good way to determine what the exact roller gap was.

Given the common advice to use a credit card as a way to achieve a 0.030″ gap, believed by many to produce a pretty ideal crush size, that’s what I did for the coarse batch. For the fine crush, I tightened the gap all the way down then backed off a very slight amount, just enough so that no knurls were touching.

My experience milling the first batch was pleasant, the grain flew through the rollers without issue. On the other hand, the fine crush batch took a few minutes longer and resulted in my drill slipping off the drive shaft a couple times.

The resultant grist appeared quite pulverized, a stark difference from the familiar looking crush of the coarse batch.

As each batch of strike water was done heating, they were transferred to separate MLTs before mashing in to achieve the same target mash temperature.

Each batch was briefly stirred at 15 minute intervals throughout the 1 hour mash rest. Using the no sparge method, I collected equal volumes of sweet wort from either batch.

Lautering time between the batches was about the same, which may be a function of the fact I used fabric filters in both MLTs; it’s possible the finer grain bits would have clogged a false bottom or stainless braid.

Both batches of wort were boiled for 60 minutes with hops added at the times listed in the recipe.

At the completion of each boil, I quickly chilled the wort to my target fermentation temperature.

It was at this point I took hydrometer measurements, admittedly expecting to find a stark difference, yet was shocked to discover both batches at the exact same OG.

Identical fermentors were filled with equal amounts of wort from either batch then placed in my cool fermentation chamber set to maintain 66°F/19°C. I split the yeast starter into equal amounts, pitched, then hit each batch with 60 seconds of pure O2. Fermentation activity was observed within 12 hours, and both were fermenting vigorously enough the following day to require a swap from airlocks to blowoff tubes.

With signs of activity appearing to wane a week in, I bumped the temperature up a but and added the dry hop charges. After 5 days on the dry hops, all observable indicators of fermentation were absent, so I took hydrometer measurements confirming both batches had attenuated to the expected FG.

I transferred the warm beer to kegs and let them cold crash overnight in my keezer before fining with gelatin.

After a brief period of burst carbonation, I reduced the CO2 to serving pressure and let the beers condition another few days before presenting them to tasters. Both appeared equal in terms of clarity and carbonation at this point.

| RESULTS |

A panel of 20 people with varying degrees of experience participated in this xBmt. Each taster, blind to the variable being investigated, was served 2 samples of the coarse crush beer and 1 sample of the fine crush beer in different colored opaque cups then instructed to select the unique sample. Given the sample size, a total of 11 correct selections (p<0.05) would have been required to achieve statistical significance, while only 5 tasters (p=0.85) chose the different beer. These results indicate participants were unable to reliably distinguish a beer produced with grains crush very fine from the same beer made with more coarsely crushed grains.

My Impressions: As is often the case, there were a few times I was drinking these beers side-by-side where I nearly convinced myself I was perceiving a slight difference, though describing that difference was difficult. However, multiple “blind” triangle tests proved whatever I thought I was detecting was more likely due to bias than actual differences, as I was incapable of reliably distinguishing the odd-beer-out. The beers were fantastic, for more on that, check out the recent The Hop Chronicles on Huell Melon.

| DISCUSSION |

The fact participants in this xBmt were unable to reliably distinguish a beer made with finely crushed grains from the same beer made with coarser grains is surprising to me. I was confident this variable was going to produce differences in beer character, overall efficiency, and perhaps even appearance, an assumption influenced in large part by anecdotes from other brewers as well as our first xBmt on the impact of crush size. While we’re not interested in pretending to know why things happened the way they did, the other contributors and I spent some time speculating about these results. One theory is that there is a point at which the relationship between crush size and extraction rate plateaus, that milling finer than a certain size won’t increase extraction. This does little to explain the disparity between these results and those of our initial crush size xBmt, as those 2 batches were crushed at similar mill gaps. Is it possible the effect of crush size is positively correlated with OG? Assuming the differences observed between the Imperial Stouts from the first xBmt were a function of crush size and not some extraneous variable, it seems at least plausible the higher amount of grain and resultant OG may have played a role.

We also discussed the possibility of a relationship between crush size and conversion speed, pondering the possibility that the fine crush batch had achieved full conversion earlier than the coarse crush batch. It makes practical sense that fine crushed grain makes starch more easily accessible to enzymes while the larger endosperm chunks in coarse crushed grain will take longer to dissolve. But again, this is just speculation. Since I tend to mash for 60 minutes and highly preferred the ease of milling the coarse grain, I reset my mill gap to the 0.030″ thickness of a credit card, where I plan to leave it.

If you have experience with milling grain at difference sizes, please share your thoughts in the comments section below!

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