To elaborate, the recipe I have was for 20 litre batch at OG 1046. I used my 12 litre (safely boilable) pot to mash the 4.3 kg grain bill specified for a 20 litre batch. My problem was that I only ended up with 12 litres of wort at 1044 in my FV after liquoring back.

Despite keeping the amount of grain the same I didn’t end up with wort concentrated enough to get near my 20 litres target.

Was it ever possible meet the 20 litre volume with my 12 litre pot?

Otherwise, I can’t work out where I went wrong.


UPDATE: As requested, this update gives the recipe used, which is the Munich Helles from James Morton's book, BREW. However in terms of method I didn't follow the books Lager Method in terms of water quantities as I decided to use a 12 litre pot for mash/boil and use the liquor back approach which is discussed in the book albeit in an on/off manner throughout the book. (FYI The book suggests it's possible with a 10 litre pot, but its never discussed wrt to a specific recipe)... (i'd recommend the book though).

OG 1.046-1.048
FINAL GRAVITY 1.011-1.013
ABV: 4.5% - 4.7%

20 Litres
Estimated Efficiency 70%

Pilsner Malt, German 4.3kg (9.5lb)
(I asked for the grain to be crushed, the MaltMiller.co.uk did this for me)

First wort hop: Hallertauer (4% AA) 40g (1.5 oz)
Aroma Steep: Hallertauer (4% AA) 60g (2.125 oz)


1 IRISH MOSS TABLET (I used Protofloc)

The Method
Prepare a starter a week before in 2 phases from 2 pure yeast sachets, based on a yeast calculators estimate of my required cell count.

MASH IN I insulated the 12 litre pot with 4 layers of large bubble wrap and string and lined it with the grain bag. I filled it the with 9 litres at 69.5°C , as 2:1 ratio is quoted as a minimum, and poured in the 4.3kg grain, and pushed the grain down with a plastic paddle so the water covered it. I then stirred a little so that there were no obvious clumps of dry grain. The water temperature dropped to 50°C (ish), although it was impossible to get a confident reading, as it was so thick. I then added just boiled water in 500 ml increments until i was getting my target 65°C and started a 1 hour timer and put the glass lid on. I checked this approximately 15 min intervals and it appeared to approximately hold the temperature for the whole hour (again it was hard to know if the reading was representative of all the pot.) i believe there was about 11 litres of water in the pot, at this point.

MASH OUT I attempted to raise the grain temperature, initially on maximum heat (gas), to 75°C but i had a differential of about 15C between the edge of the pot at (85C) and the centre of the grain at (70°C), I kept trying to stir the grain but to no real avail over 15 mins. I effectively gave up and moved onto the sparge.

SPARGE I pulled out the grain into a massive caterers mixing bowl and poured over 2 litres of water at 75°C, and let it rest for 10 mins. The grain was sat in the water as all the grain and the 2 litres of water fit in the bowl. In hindsight - Perhaps the bowl should have been intentionally small so that water in the grain bag would drip into the bowl rather than soak into the grain more? After the 10 mins was up, i gently squeezed the grain bag and I poured the water from the bowl into the pot with the wort and dumped the grain.

BOIL I should have taken a starting gravity reading here, but i didn't! I did however use my glass thermometer to allow me to calculate the volume of wort as being 5.5 litres.

I added my first wort hops and put maximum heat on and brought the wort to a boil (no lid), I now added 2 more litres of water (i think should have done before it started boiling) i figured it was better to add more water before boil completion as it would definitely be sanitary, perhaps there is a better reason not to do this? I let it boil for 90 mins (no lid). 15 mins before the end of boil I added 1 Protofloc tablet.

STEEP I added about 1 litre of cold sanitary water and got the temperature between 75°C and 79°C, added the aroma hops and let them steep for 30 mins.

LIQUOR BACK I took a gravity reading, and using a online calculator worked out the gravity at 20°C was 1.105 (i think), i was sure how water to add so i just added some and got to just under 12 litres at 20°C and what i settled as being my Original Gravity of 1.044, meaning i diluted it too much without getting near 20 litre batch, hence my reason for this post.

COOL for PITCHING I put the lid on and sealed it with starsan covered clingfilm and placed the pot in the sink in cold water (7°C). This took me hours, as i didn't have ice and only half the pot was in contact with the cold water. [I'm going to make a wort chiller even for this smallish pot or at the very least boil and freeze some water the night before to liquor back with.]

The target was stated as being 8°C, but as the yeast is happy at 8°C to 12°C, i ended up settling for 12°C before i transferred to FV and dumped all the yeast in and gave it a good shake. My FV fridge is set to 8°C and certainly fermentation had started 24 hours later, but it was by no means a vigorous airlock bubbling like you get with an ale at 20°C.

I realized later my yeast amount was for a 20 litre, so i presume i've over pitched, but i understand that's preferable to under pitching, but that has nothing to do with my mash efficiency which is the suspected reason for my poor wort concentration.

2 Answers 2


You just had very poor mash efficiency.

All the causes and solutions have been covered in other Q&A here.

When done correctly you should be able to easily produce 10l of 1.096 wort post boil and dilute to 20l for 1.046

Update: Ran some of your numbers. DP fine, water/grist ratio fine. Looks like you actually got ok mash efficiency but saccharification may not have completed. Your overall efficiency was also dropped by the grain absorption (5 liters) and the sparge/rinse method wasn't effective.

Moving forward: Iodine check the mash for completion rather than a timer.

Suspend the grain bag above the pot to let drain. Then put the grain bag in a strainer bowl above the pot, pour 168F water through the grain into the pot to get 10l total wort volume. Squeeze the grain bag to get the grain dry as possibe. This should get you close to the 1.096 10l target.

  • 1
    Thanks, I thought this might be the case really but I followed the process closely, but the only think being different was the pot and amount of water I used for mash and boil. Can you point me to some tips for improving mash efficiency you suggest using my 12 litre pot?
    – AlexS
    Mar 31, 2018 at 22:44
  • @AlexS your mash was probably just really thick and didn't get a good rinse, even a thick mash will complete in time. Just check with iodine test to know ehenbits done. Mar 31, 2018 at 23:17
  • 1
    thanks I’ve never heard of the iodine test, I just looked it up it sound very inexpensive and simple to do so’ll definitely do that test next time. For anyone interested I read this article at the link below. In terms of improving efficiency in my 12 litre pot, would a small pump help by recirculating the water, assuming I can keep the temperature constant over the hour?byo.com/article/successful-mash-conversion-tips-from-the-pros
    – AlexS
    Apr 1, 2018 at 9:57
  • 1
    @AlexS updating your question with your recipe and the method you used to mash would help us address what caused the suspected poor efficiency. Exact grains, estimated mill size, what temps, how long, stirring?, strike water ph, etc all play critical roles. Apr 1, 2018 at 12:46
  • As requested i've update the question with the recipe and method.
    – AlexS
    Apr 1, 2018 at 15:08

If I understand correctly you're trying to mash the same amount of grains in less water with the intention to add water later to reach the planned volume and OG.

While that's, I suppose, hypothetically possible it's very hard at least. The ratio between water and grains is important. As the ratio of grains goes up, the efficiency of the mash goes down. The reason being, in layman's terms as I don't know any better, that there's a limit to how much sugars the water can act as solvent on.

You could solve this by doing multiple mashes/boils with the right water to grain ratios and then just combine them. Simply split the process up.

Or.. you could just get a bigger pot. 🙂

Often people add elements to food grade buckets and do the process that way. Something to look into?

  • You understood correctly, although liqoring back isn’t a hypothetical method, it is something people do practice, but clearly I don’t know enough about it yet.
    – AlexS
    Mar 31, 2018 at 22:40

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