Author: Matt Del Fiacco

In brewing, there are various decisions one makes that are said to have a noticeable impact on the final beer, levers that can be adjusted by the brewer to produce a predictable outcome. One such example is mash temperature. As a function of enzymatic activity, a beer mashed at a lower temperature will experience higher attenuation and thus finish at a lower specific gravity (SG) than one mashed warmer. Seeing as yeast metabolize sugar during fermentation, the idea that mash temperature can be used to adjust the perceptible sweetness of beer makes practical sense.

Curiously, the results of multiple past xBmts on mash temperature have failed to uphold this notion. Despite the differences in attenuation and level of alcohol, tasters have generally been unable to tell apart beers mashed at different temperatures. While surprising to many, one possible explanation for those results is that the beers brewed in each xBmt were pale, clean, low OG styles. It’s been suggested that mash temperature might have more of an impact on a higher OG beer fermented with a characterful Belgian yeast strain.

For me, the mash temperature xBmts have been some of the most shocking. This is due to both the frequent insistence that even small differences in mash temperature matter as well as the myriad papers out there discussing the chemical impacts of mash temperature. Given the objectively observable results from past xBmts, clearly it has an impact, but the fact it wasn’t perceptible had me scratching my head. Like others, I began to wonder if the prior inconclusive results might be due to the beer style and put it to the test with a big Belgian ale.

| PURPOSE |

To evaluate the differences between Belgian Ales mashed at either 148°F/64°C or 164°/73°C.

| METHODS |

With the hope of keeping any differences as apparent as possible, I went with a pale Belgian Golden Strong Ale.

Bandages

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 4.5 gal 90 min 26.3 IBUs 4.2 SRM 1.081 1.015 8.8 % Actuals 1.081 1.014 9.0 % Fermentables Name Amount % Pilsner (2 row) (Gambrinus) 14 lbs 100 Hops Name Amount Time Use Form Alpha % Magnum 13 g 90 min First Wort Pellet 12 Czech Saaz 12 g 30 min Boil Pellet 3.5 Yeast Name Lab Attenuation Temperature Gnome (B45) Imperial Yeast 74% 65°F - 75°F Notes Water Profile: Ca 54 | Mg 11 | Na 25 | SO4 81 | Cl 65 Download Download this recipe's BeerXML file

I kicked off my brew day by collecting the water for each full volume batch, adjusting to my desired profile, then setting the electric controllers to heat them up.

As the water was heating, I weighed out and milled the grain for each batch.

With the water properly heated, I added the grains, kicked the pumps on, then checked to make sure both hit my intended mash temperatures of 148°F/64°C and 164°F/73°C.

Following each 60 minute mash rest, I removed the grain baskets and let the drain while the wort was heating up.

At this point, I stole some wort from both batches, briefly boiled and chilled them, then pitched a pouch of Imperial Yeast B45 Gnome into each.

Both worts were boiled for 90 minutes with hops added at the times stated in the recipe.

With each boil complete, the wort was chilled and racked to separate fermentation kegs, at which point I to hydrometer measurements showing a slight difference in OG.

The fermenters were placed in a chamber controlled to my desired 72°F/22°C pitching temperature and allowed to finish chilling overnight, at which point I pitched the yeast starters, set the temperature controller to 74°F/23°C, and left the beers alone.

After 3 days of fermentation, I began raising the temperature 2°F/1°C per day over 5 days until they were at 84°F/29°C, where they sat for a week to finish up. Hydrometer measurements showed the high mash temperature beer finished 0.006 SG points higher than the low mash temperature batch, amounting to 81% attenuation and 8.4% ABV for the low mash temperature beer compared to 74% attenuation and 8% ABV for the high mash temperature beer.

I left the beers alone 2 more days before verifying no change in FG and pressure transferring them to separate sanitized kegs.

The filled kegs were placed on gas in my keezer and allowed to condition a couple weeks before they were ready to serve to tasters.

| RESULTS |

A total of 23 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the low mash temperature beer and 1 sample of the high mash temperature beer in different colored opaque cups then asked to identify the unique sample. A total of 12 tasters (p<0.05) would have had to identify the unique sample in order to reach statistical significance, though only 10 made the accurate selection (p=0.21), indicating participants in this xBmt were unable to reliably distinguish a high OG Belgian Ale mashed at 148°F/64°C from one mashed at 164°F/73°C.

My Impressions: Out of the 5 semi-blind triangle tests I attempted, I picked the odd-beer-out 3 times, which is only slightly better than chance. While bias was undoubtedly at play, if forced to describe a difference, I’d say the high mash temperature beer had a slightly more pronounced Pils malt flavor. I didn’t perceive anything I would attribute to differences in ABV, neither were particularly sweet, and both were quite tasty!

| DISCUSSION |

It is well established that mash temperature is negatively correlated with wort fermentability, and this easily measurable fact has led to the belief that it consequently impacts the perceptible dryness and sweetness of beer. It’s an idea that’s been embraced by brewers the world over for a very long time– mash low for a dry beer, mash warm to increase body and sweetness. While some contend the effect is less noticeable in simpler styles, the fact tasters in this xBmt were unable to tell apart a high OG Belgian ale mashed at 148°F/64°C from one mashed at 164°F/73°C indicates the objective difference may not lead to a perceptible one.

While the sensory analysis findings were, like past mash temperature xBmts, inconclusive, the beers were undeniably different. As expected, the beer mashed cooler had a lower FG and higher ABV than the one mashed warmer, implying mash temperature can be used as a lever to control alcohol content. This alone may be helpful for brewers of session beers where lower ABV is often accompanied by less flavor; by raising the mash temperature, one could get away with using more grain while keeping the alcohol restrained.

The lack of a perceptible differences between these xBmt beers further supports the hard-to-swallow idea that higher FG isn’t necessarily related to beer viscosity. While this has been shown to be the case multiple times now, one possible explanation is that carbonation of the beer covers up any differences in mouthfeel. A future mash temperature xBmt on a less carbonated style may provide a better understanding of this point.

More often than not, I mash my beers around 152°F/67°C and will likely continue to do so for the most part. When brewing more sessionable styles where I want a lot of flavor, I’ll definitely consider bumping the temperature up a bit, but only for the purpose of controlling ABV, not dryness or mouthfeel.

If you have any thoughts about this xBmt, please do not hesitate to share in the comments section below!

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