Author: Brian Hall

Brewing beer is a relatively time intensive process, which is a commonly cited reason some people aren’t able to brew as often as they might like. While there’s little one can do to get around certain aspects of brewing such as preparation and packaging, there’s been quite a bit of focus lately on ways to break up the amount of time required to make a batch of beer. We’ve shown over numerous Short & Shoddy brews as well as a previous xBmt that reducing the mash rest by 30 to 40 minutes doesn’t seem to have an impact on beer flavor, though there’s some evidence it leads to less conversion. For the hobby brewer with a busy schedule, this is one way to squeeze in more brewing, though there is another option that’s been getting some attention lately.

I’ve been performing extended mash rests, sometimes overnight, for a few years now, an approach involving mashing in one evening then collecting the wort and finishing the brew the next morning. Advocates laud this method for allowing them to break up their brew day while having no negative impact on their beer. However, overnight mashing has its critics as well, those who claim it produces lower quality wort due to the natural loss of mash temperature, which can lead to over-conversion and ultimately a thinner bodied beer.

For the homebrewer relying on a kettle or converted cooler MLT to mash in, the temperature can drop anywhere from 2°F/1°C to 8°F/4°C over the course of an hour. Obviously, stretching the mash rest out by 10 or more hours results in an even more drastic drop in temperature, but does it really lead to a beer that’s noticeably different than one that’s mashed under normal circumstances?

| PURPOSE |

To evaluate the differences between a beer that was mashed for an extended amount of time (15 hours) and one that was mashed for the standard 60 minute rest.

| METHODS |

I chose a simple Pilsner recipe for this xBmt to allow any differences in the variable to shine.

Despacito

Recipe Details Batch Size Boil Time IBU SRM Est. OG Est. FG ABV 5.5 gal 60 min 31.6 IBUs 3.9 SRM 1.049 1.011 4.9 % Actuals 1.049 1.011 5.0 % Fermentables Name Amount % Pilsner (2 Row) Ger 9.5 lbs 95 Munich Malt 8 oz 5 Hops Name Amount Time Use Form Alpha % Tahoma 16 g 60 min Boil Pellet 6.9 Tahoma 25 g 20 min Boil Pellet 6.9 Tahoma 30 g 5 min Boil Pellet 6.9 Notes Water Profile: Ca 69 | Mg 0 | Na 0 | SO4 74 | Cl 68 Download Download this recipe's BeerXML file

The day before starting the overnight mash, I RO filtered my brewing liquor and adjusted it to my desired profile.

The following day, I began heating the water to strike temperature with my heat stick in preparation for an evening mash in.

As the water was heating, I weighed out and milled the grains for both batches.

Once strike temperature was reached, I mashed in and gently stirred to incorporate the grains before checking my mash temperature was correct.

And that was it for this portion of the brew day, it took all of 20 very hassle-free minutes. I wrapped my mash tun with insulation to preserve as much heat as possible then ran in to read a bedtime story to my son.

The next morning started like any normal brew day with the heating of RO water I’d collected the previous day and adjusted to the same profile as the other batch. After mashing in, I checked the temperature of the overnight mash batch and found it had dropped a whopping 82°F/46°C over the 15 hour saccharification rest. Meanwhile, the 60 minute mash hit the same original target temperature.

From this point forward, both batches were treated identically. I removed the grain bags from each kettle once the 60 minute mash was complete then hit the flames under each, measuring out hops while they were heating.

Given the lower temperature of the overnight mash wort, it came to a boil 15 minutes after the 60 minute mash wort. Both worts were boiled for an hour with hops added per the recipe.

At the completion of each boil, I quickly chilled the worts to my target fermentation temperature of 50°F/10°C before taking refractometer readings showing the overnight mash wort had a higher OG than the 60 minute mash wort.

I racked equal amounts of each wort to separate 6.5 gallon glass carboys that were placed in my temperature controlled fermentation chamber.

Each wort was then pitched with a single can of fresh Imperial Yeast L28 Urkel.

The beers were showing similar signs of fermentation within 16 hours. After 3 days of activity, I gently raised the temperature in the chamber to 62°F/17°C then left them alone until fermentation was complete. Hydrometer measurements after 16 days total revealed the overnight mash beer dried out slightly more than the 60 minute mash beer.

I then kegged the beers.

After a brief cold crash in my keezer, I fined the beers with gelatin then let them lager 4 weeks on gas before serving them to unwitting participants.

| RESULTS |

A total of 22 people of varying levels of experience participated in this xBmt. Each participant was served 2 samples of the overnight mash beer and 1 sample of the beer mashed for 60 minutes in different colored opaque cups then asked to identify the sample that was unique. At this sample size, 12 tasters (p<0.05) would have had to select the unique sample in order to reach statistical significance, though only 8 (p=0.46) made the correct selection, indicating participants were unable to reliably distinguish a Pilsner made using a 15 hour mash rest from one made using a more traditional 60 minute mash rest.

My Impressions: These beers tasted the same to me over the course of several weeks, regardless of temperature and carbonation levels. After pouring several samples, I noticed the overnight mash beer had almost no head retention. Even after a quick swirl of both beers, the head on the overnight mash beer fell off within 10 to 20 seconds. I was only able to select the odd-beer-out 2 out of 7 attempts, which is right in line with random chance. Knowing the variable, I expected I would have been able to notice a mouthfeel difference from the drier beer, but that was not the case, as both beers tasted smooth with a crisp finish. It’s always great to have a simple Pilsner on hand!



| DISCUSSION |

Given what we’ve all been taught about the mash, it seemed plausible a significantly extended saccharification rest might produce a noticeably different result than a 60 minute mash for a few reasons. Maintaining a stable mash temperature for so long would be next to impossible for most homebrewers, leading to a fairly dramatic drop that could be posited to not only produce a thinner bodied beer, but increase the risk of lactobacillus growth. However, the fact participants in this xBmt were unable to reliably tell apart a beer mashed for 15 overnight from one mashed for 60 minutes, providing some support for those who have using the method with success.

The sensory data may have shown no perceptible differences, but there were some objectively measurable differences between the beers. Perhaps as a function of the longer mash rest, not only was the OG of the overnight mash beer slightly higher, but it also finished with a lower FG, leaving it about 1% ABV higher than the 60 minute mash beer. If this was due to some wild microbe, it didn’t throw off any noticeable aroma or flavor compounds, leaving me to believe it was most likely due to greater extraction.

I can’t say I was completely shocked by these results, I’ve performed many overnight mashes without issue, but the fact neither tasters nor I could distinguish the ABV difference in such a light beer did spin my wheels. In the end, mashing for extended lengths is likely something I won’t be doing often, mostly because of the exBEERimental nature of my brewing these days, but I definitely see it as a viable method for turning a single long brew day into a couple shorter sessions.

If you have thoughts about this xBmt, please feel free to share in the comments section below!

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