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Overnight-Full Volume Mash

Posted by madcowbrewing on 8/26/2015 at 12:16:24 AM

I am a great fan of methods that make things easier, and the overnight mash is certainly a time saver. But I have always wondered if it was possible to maximize the savings by doing a full volume mash (no-sparge) combined with the overnight aspect of it. Whenever I did an overnight mash, I still had to get up, start the water for the sparge and then spend the time to either fly sparge or batch sparge…..where did my time savings go?

So first to understand that an overnight sparge is okay and works you have to consider the following:

Attenuation - If you are making anything you do not want bone dry, forget it. This long, slow mash leads the best for those styles that attenuate almost fully. Like a Saison, some Belgian styles, etc. Be sure the recipe you want on this mash is prepared for a low final gravity.

Possibility of souring or bacteria - Any time your mash temp drops below 130 degrees F the Lactobacillus that live naturally on the grain, have the potential to grow and sour and infect your wort. If you keep your temperature of your mash up, you should have no problems.

Insulating your mash tun - When you mash overnight you want to minimize the temp loss as much as you can. You do want to stay above the 130 threshold….preferably higher than that. So in order to do that, I employ a three tier system. First, I place a heating pad under the mash tun, one that does not have an auto shutoff. Turn that on high. Second, I wrap my tun with a Ferm Wrap heater. And last, I wrap it in a heavy blanket. This works well for me and I only lose about 10 degrees over a 9-10 hour mash.

To quote Mr. Wizard from BYO:

Mashing is all about enzymes. The two key enzymes in mashing are alpha-amylase and beta-amylase. Beta-amylase produces maltose from starch and is most active between 140-149 °F. The thing about beta-amylase is that it stops working when it runs into a branch in the starch molecule. That’s where alpha-amylase comes to the rescue. Alpha-amylase randomly reduces big starch molecules into smaller pieces. Its temperature optimum is right around 158 °F.

The key to this method is keeping the temperature high at the beginning as you will lose some degrees based on how you insulate your mash tun. When the two (Alpha and Beta) enzymes work together, the result is an increase in wort fermentability.

Now that we understand the overnight mash and how it works, I wanted to reduce that extra step in the morning of the sparge by doing a full volume mash. Some were saying that I would lose potential sugars due to not rinsing the grains (sparging). I was not sold. I had to find out.

So I devised a plan to register all the factors going through this procedure and see for myself. Was my mash getting the efficiency I wanted? Will I lose sugars and get a lower efficiency due to not sparging?

My plan was to crush my grain just like I would on a normal brew day, no deviations, right? Heat up my full volume of water I needed to not sparge and get the amount of wort I needed for the boil. And finish the next day with the boil, and to prove if I missed any sugars, to do a quick sparge on the grains and see what I got. Yes, I know…..this defeats the full volume savings I will get, but at least I will be doing it while the boil is going on.

My recipe was a re-work of my house Saison recipe. I wanted to tone down the alcohol level so that drinking two won't put you out. And I was going to add some lemongrass to this one. Since I wanted it super dry on the finish, this recipe was perfect for this experiment. The following were my findings:



Out on the Farm Saison


Beer Info

Grain (lbs)


Batch Size (gallons)


Full Volume Strike Water (gallons)


Strike Temp  (°F)


Starting Mash Temp (°F)


Finished Mash Temp (°F)


Time Mash Started


Time Vourlaf started


Time Wort ran clear


Time Mash finished

8:35am, 575 minutes (>9.5hrs)

Target Volume, pre-boil


Actual Volume, pre-boil


Target Gravity (, pre-boil


Actual Gravity (, pre-boil


Measured Mash Efficiency




Sparge water for starter wort (gallons)


Sparge water Temp (°F)


Extracted volume from Sparge

stopped @ 1.5 gallons

Extracted Gravity from Sparge (


In conclusion, you can take away that doing the overnight mash only had the effect of the temperature drop. And if the beer you want to make can incorporate the lower mash temp in conjunction with the higher temp to start, then this is an easy way to break up your brew day and save you some time overall. The full volume mash seemed to have no effect on my efficiency as some were saying and I wanted to prove one way or the other. The small sparge I did to verify if I left sugars behind did prove that there was some left, but I am left wondering if I had collected the extra 1.5 gallons when the runoff decided to get to 1.010 and had 8.5 gallons going into the boil, where would I be then? A lower gravity wort with more gallons then I needed. I would have 8.5 gallons at 1.036 and my efficiency would be at 78%. You could theorize that if I lowered the original water volume that I would have rinsed the sugars out earlier than 8.5 gallons collected... but I don’t think that it would have. I think the overall take away is that as a homebrewer we can dial and tweak our recipes, equipment, and procedures and still make great beer. Sometimes we want to do that and reduce the time it takes to do all that. I hope this helps those who are looking at playing around with either the overnight mash or the full volume no sparge mash.


Tags for this post: overnight, mash, souring, fermntability

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