Author: Matt Waldron

When I started brewing about 3 years ago, I jumped right into all grain using 1 gallon kits then soon after bought a batch sparge setup with converted coolers for larger batches. I made many good beers, no doubt, but I found myself pining for a less complicated method, one that didn’t involve as much setup or clean-up but resulted in a finished product with similar quality. It wasn’t until a year or so later I learned about Brew In A Bag (BIAB) and, amid a run to win my homebrew club’s Homebrewer of the Year title, abruptly adopted it as my primary approach after buying a used e-BIAB system on a whim, sending me down a much simpler and less time consuming path.

As the popularity of BIAB continues to grow, and grow it certainly does, brewers are learning that particular variables, once accepted as convention, differ when using this modern approach. One such variable that has garnered quite a bit of attention lately is crush size, with the BIAB contingent contending the use of a fine mesh bag allows them to essentially pulverize their grain to the point of flour, much finer than the coarse grist required when fly sparging to ensure a proper lauter. Multiple anecdotal observations have demonstrated finer grinds seem to improve overall efficiency, a plus for those looking to get more out of their grain, but I still wondered– does crush size impact anything else?

| PURPOSE |

To evaluate the impact crush size has on 2 beers of the same recipe brewed separately with either fine or coarse milled grains and otherwise treated exactly the same.

| METHODS |

To make sure I got a solid look at all of the above mentioned aspects, I thought it best to go with a big Russian Imperial Stout, which was graciously provided by the fine folks at HomeBrewSupply.com.

Batch Size Boil Time IBU SRM OG FG ABV 5 gal 75 min 85 60 1.080|1.090 SG 1.028|1.020 SG 9.2%

Fermentables

Name Amount % Maris Otter 16 lbs 81 Roasted Barley 1 lbs 8 oz 7.6 Special B 1 lbs 5.1 Crystal 60L 12 oz 3.8 Chocolate Malt 8 oz 2.5

Hops

Name Amt/IBU (Tinseth) Time Use Form Alpha % Magnum 85 g/85 IBU 75 min Boil Pellet 11.6%

Yeast

Name Lab Attenuation Ferm Temp WLP001 California Ale Yeast White Labs 78% 66°F

The all-grain kits arrived well packaged with perfectly pre-measured grains to ensure both beers would be equal and fit for the xBmt.

Two days prior to brewing, I prepared separate starters of equal size and pitched each with 2 packs of WLP001 California Ale Yeast.

Both starters were crashed approximately 24 hours later in preparation to be decanted and pitched.

Due to time hampering circumstances, I brewed these batches approximately 8 hours apart. While the same exact equipment and processes were used for both batches, a concerted effort was made to ensure equality in all other areas.

I milled both sets of grain consecutively, starting with the coarse grist, running it through my 2-roller mill with a gap setting of 0.039 inches (1 mm), which cracks the hull and exposes the starch without completely demolishing the grain. This is a common default setting for many popular homebrew mills.

Once that was complete, it was time for me to mill the fine grist, but first I had to decrease the gap between the rollers. To do this, I loosened the appropriate roller and carefully moved it closer to the other roller, using a caliper to determine when they were approximately 0.025 inches (.5 mm) apart. My goal here was to essentialy pulverize the grains to a near flour-like state, something many BIAB brewers view as a luxury of their method since it is believed to improve their efficiency without any risk of a stuck sparge.

With both sets of grain ready to go, I set out to brew the first batch using the coarse grist. The mash held a steady 149°F/65°C for an hour before I collected the sweet wort and brought it to a boil. Hoping for a big, rich Imperial Stout, I was slightly disappointed when a hydrometer reading close to the end of the boil revealed the SG was lower than expected. To encourage a bit more evaporation, I added an additional 15 minutes to the length of the boil. Once complete, I quickly chilled the wort to 70°F/21°C and racked it to a sanitized fermentor before measuring the OG– 1.080. Substantially lower than the 1.100 I was hoping for. Oh well, it was getting late and I had some cleaning to do in preparation for the next morning’s brew. I pitched the yeast, shook the fermentor for 3 minutes, then placed it in my temp controlled fermentation chamber.

I returned early the following morning, approximately 8 hours later, to brew the fine crush batch. Second verse, same as the first. The mash temp was exactly the same and I made sure to adjust the boil length to 75 minutes. Following the chilling of the wort, I measured the OG and discovered the first objectively observable impact of crush size– this batch came in at 1.090. The 70°F/21°C wort was racked into an identical fermentor as the coarse crush batch, yeast was pitched, then I shook it for 3 minutes before popping it into the fermentation chamber.

Both beers took off quickly and were plugging along with seemingly similar vigor by the following morning. After 6 days in the chamber, both batches appeared to have calmed down, so I took a hydrometer measurement to see how things were going. What I observed suggested these beers might be taking different paths. The coarse crush beer was sitting at 1.030 SG and appeared visibly paler with less clarity than the fine crush beer, which had dropped to a much lower 1.021 SG. Interesting since the coarse crush batch got an 8 hour head start. I left the beers to finish up, ramping the temp a bit to encourage complete attenuation, then returned a week later for another check– no change.

A less stubborn brewer might have called it a day and packaged the beer. I am not that brewer. Rather, I added a tablespoon of yeast nutrient to each fermentor in hopes of driving the SG down a bit more, this led to a slight increase in airlock activity and bubbling on the surface of each beer. Since these beers had higher starting gravities, I let them sit in primary longer than I might with more coarse strength beers. At 29 days post-pitch, I took a final SG reading and found the coarse crush beer had dropped a smidge to 1.028 SG while the fine crush beer was at 1.020 SG.

It was at this point the beers were cold crashed, hit with some Biofine, then kegged and force carbonated. I allowed them to condition for about 2 weeks in my keezer before presenting them to participants. While both were looking good, there were some noticeable differences with the coarse crush beer appearing quite a bit lighter than the fine crush beer.

| RESULTS |

Forty-four people in total participated in this xBmt with representation from BJCP judges, experienced homebrewers, a few professional brewers, and craft beer drinkers. All of the data was collected in approximately 1 hour at the FIU Southern Brew Festival where I made sure to start early and stop before fest-goers imbibed too much. Each taster was served 2 samples of the coarse crush beer and 1 sample of the fine crush beer in colored opaque cups then instructed to identify the different one. To achieve statistical significance with this sample size, 20 people (p<0.05) would have had to make the accurate selection. All said and done, 24 tasters (p=0.001) correctly identified the fine crush beer as being different, providing support for the notion that crush size has an impact on more than just efficiency, but the ultimate characteristics of beer as well.

The participants who made the correct selection on the triangle test were then asked to complete a brief comparative evaluation. Out of the 24 respondents, 15 (62.5%) endorsed the fine crush beer as being the one they most preferred while 6 said the preferred the coarse crush beer and 3 said they had no particular preference. The same number of tasters responded correctly when asked to guess which batch was brewed using a finer crush, the other 6 wrongly choosing the coarse crush beer.

My Impressions: When presented these beers in a quasi-blind triangle, I was consistently able to distinguish them. I perceived the fine crush beer as having a fuller mouthfeel, greater complexity, and subtle alcohol twang in the finish. While my preference leaned toward the fine crush beer, the coarse crush sample certainly wasn’t bad! I experienced it as possessing a stronger roast character that was somewhat sharp and quite pleasant, although it came across much thinner than the fine crush beer and had qualities more consistent with Robust Porter than Russian Imperial Stout. In fact, I’ll be stowing a few bottles of the coarse crush beer away with plans to enter it as a Porter in a future competition. Either way, I was quite pleased with the recipe and would happily recommend the Home Brew Supply RIS kit to anyone looking to make this delicious style!

| DISCUSSION |

On the surface, it would appear crush size makes a difference, not only supporting the popular notion that a finer crush improves efficiency, but also produces a beer that’s reliably distinguishable from one made with coarser crushed grain. Cool, but some of the other data observed in this xBmt was unexpected and left me scratching my Movember stubble.

The fact the coarse crush beer had a lower OG than that of the fine crush beer yet finished with a higher FG was confounding to me. I would have at least expected both batches to be be within a similar attenuation range, but that didn’t happen, not by a long shot– the coarse crush batch was at 63% while the fine crush batch had a drastically higher 76% attenuation. Could this really be a function of crush size alone? In researching the topic, I discovered little in the way of prior investigation, though found a similar experiment done by Kai Troester on a lower OG beer. His results also showed that a finer crush did increase efficiency, but attenuation was noted to be independent of crush size. I kept digging and finally stumbled on a very old Brewer’s Journal research article that stated,

Of the different grades of grist, the fine meal takes longer to saccharify than the grits, but furnishes worts that attenuate further than those from the grits and husks.

I’m not sure what to think. I took every step possible to ensure both batches were treated equally in every respect except crush size, I even took measures to encourage the complete attenuation of both beers (nutrients, extended primary, etc.), and neither showed any signs of contamination. If the differences were caused by something other than the variable tested, I’m at a loss for what it might be.

It’s apparent our understanding of the impact crush size has on beer is quite limited and I look forward to learning more about this interesting variable. With the heaps of anecdotal observations combined with the slightly more objective data regarding crush size and efficiency, I’m comfortable saying a finer crush will likely increase one’s efficiency. However, given the paucity of research on this topic in general, I’d caution anyone from using this single point of data to justify a previously held belief or a change in process.

What has your experience with crush size been? Did you notice changes to anything other than efficiency when you changed your milling process? Please share your thoughts in the comments section below!

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