Full Volume Mash vs. Boil Kettle Dilution
METHODS MADE SIMPLE | Full Volume Mash vs Boil Kettle Dilution
As many brewers have come across in their pursuit of higher efficiency, liquor-to-grist ratios have been rumoured to make a big difference to their mash efficiency, and lautering. But many BIABers choose to use a full volume mash rather than split their volume into mash and sparge. While there are many “correct” ratios to follow, it’s what works best for the individual brewer, and their equipment that is the best approach. With the plethora of information available on the subject, it’s easy to get mixed up in what’s right, and what’s wrong, too thick of a mash and you can run into recirculation issues, reduced efficiency, and blocked pumps. Thin or full volume mashes can reduce the available space in mash tuns for large grain bills, ultimately affecting the gravity of the wort.
Mash thickness has often been stated to be irrelevant and disproven by many BIABers achieving great efficiency regardless. Some literature points to thin mashes being higher in extract yield by diluting the enzymes responsible for conversion, making it easier to convert and dissolve the sugars into the wort. Thick mashes can reduce the yield by trapping the starches and enzymes within the grain bed, preventing full conversion, and resulting in a less fermentable wort of greater quality and increased maltiness, often requiring increased recirculation and/or extended sparging to extract these trapped sugars. When it comes to extremely thin mashes such as those used in ultra-low/NA brewing, it has been noted as being less efficient due to the greater volume of water over-diluting the enzymes ability for conversion, preventing them from attaching to, and breaking apart the starch molecules.
So, what does this mean for our low gravity brewing? Should we be using a thick mash to decrease our efficiency and increase the flavour and body of our beer then top up our boil kettle to reach our full volume? Or should we be over diluting our mash to full volumes to decrease our efficiency? We take a look at.
Full Volume Mash vs Boil Kettle Dilution
For this experiment, we will run two separate mash volumes to determine the difference in efficiency, fermentability and of course, taste. One batch will be run with a full volume mash, and the other will be mashed with a lower liquor-to-grist ratio, then topped up to our full volume in the boil kettle.
Aussie Lager
| BATCH SIZE | MASH TIME | BOIL TIME | IBU | EBC | EST. OG | EST. FG | ABV |
| 8.5L | 30 mins | 30 mins | 26.0 | 7.9 EBC | 1.008 | 1.006 | 0.30 % |
| Actuals | 1.007 | 1.005 | 0.30 % | ||||
Grain Bill
NAME | AMOUNT | % |
JWM Munich, Light | 240g | 35.3 |
Simpsons Maris Otter | 240g | 35.3 |
Flaked Barley | 130g | 19.1 |
Weyermann Melanoidin | 70g | 10.3 |
Hop Schedule
NAME | AMOUNT | TIME | USE | FORM | ALPHA % |
Super Pride | 5.0g | 30 min | Boil | Pellet | 14.5 |
Super Pride | 5.0g | 10 min | Boil | Pellet | 14.5 |
Yeast
NAME | LAB | ATTENUATION | TEMPERATURE |
M54 California Lager | Mangrove Jack | 33% (Est.) | 19°C |
Water Profile: Ca2+ 64 | Mg2+ 9 | Na+ 39 | Cl⁻ 98 | SO₄²⁻ 127 | HCO₃⁻ 16 |
To start, we collect our mash water volumes for each batch and measure our grain bills. Having one mash kettle with our full volume of water and salt additions, and the other having the water and salts split between the mash kettle and the boil kettle for a lower liquor-to-grist volume during the mash.
Once the first batch has completed its mash, we remove and squeeze the bag to drain the remaining wort, check our pre-boil gravity, and transfer our full volume to our boil kettle and commence the boil.
Once the wort of the first batch has reached a boil, we start the timer for 30 minutes and add our first hop additions, continuing our way through the hop schedule. With 5 minutes left of the boil, we add our acid addition to lower the pH to our pre-ferment level of 4.7.
When the second batch is completed mashing, we transfer our wort to the boil kettle where the 7 litres of our treated dilution water is heated to 80ºC, check our pre-boil gravity, and proceed with the same boil schedule, hop additions and and acid addition.
Once both of the boils are complete, we take a sample to measure our post-boil gravities, which will be our starting gravity (SG) and to ensure we’ve reached our target pH level before transferring the hot wort to our HDPE cube to cool down to pitching temperature.
Once both of the worts have cooled down to our pitching temperature of 19ºC (66ºF), we pitch half a pack (5.0g) of Mangrove Jack M54 California Lager yeast into each cube and left to ferment in the fermentation chamber for 7 days. Once we have ensured we have reached our terminal FG, we cold crash at 2ºC (35.6ºF) for 4 days, then transfer to the kegs for carbonation and conditioning for 2 weeks.
RESULTS
– Full Volume: OG: 1.0075, FG: 1.006, = 0.3% ABV
– Boil Kettle Dilution: OG: 1.007, FG: 1.005 = 0.3% ABV
Appearance:
Crisp golden hue with a thick white foamy head.
Aroma:
Beery, malty, bready with a subtle citrus.
Taste:
Full bodied, bready/breadcrust, malty, medium-high bitterness, perfect carbonation. Faint citrus on the back end of the palette.
Overall Impressions:
Side by side, the low mash volume with a kettle dilution had an ever so slightly better mouthfeel and body compared to the full volume mash, but not enough to be a standout. While both beers were quite similar flavour wise the full volume mash finished 0.1 of a pH lower and seems to ever so slightly come through in the finish as a very minor sour twang (though barely there), which could have had a difference in the final mouthfeel. Initially the young beer had a lot of flavours still to mellow, being high in melanoidin malt it was quite overpowering with a rich bready crust/toast flavour, but after lagering on gas for many weeks, everything has balanced and taste amazing making this a perfect beer for the hot summer.
Final Thoughts
By having two exact batches with the only variable being the mash volume, we could expect to see some sort of difference in our wort composition. Instead, what we found was both batches having the same pre boil gravities and fermenter volume post boil. They also ended up with almost identical gravities post fermentation, meaning there was no substantial differences between mashing with our full volume, and mashing with a lower grist/liquor ratio and diluting in our boil kettle besides having to take more steps and calculations, which in turn means more work on brew day. The slight difference in mouthfeel and overall taste wasn’t large enough to be considered an improvement from one process over the other, and the other little variables that were present, are minute and they would be chalked up to user caused and not relevant to the different processes.
Going forward, this seems like another experiment I would like to revisit to see if I yield similar results or indeed a change in efficiency and/or overall mouthfeel, perhaps with an XPA? Being another light beer style, it would surely show through in the final results, as well trying with a heavily malted beer such as a stout.
With the current results, there doesn’t seem to be enough reason to switch from my “ease of process” full volume mashing if lieu of a post mash dilution. More tests and improved results across various styles would be needed to convince me it’s worth an extra step.
If you have any questions, or thoughts about this experiment, or are considering making or testing something similar, please feel free to get in touch with us to discuss your ideas and thoughts!