I am still having mash efficiency issues. Here's my original post: Poor mash efficiency - help please

With my last brew, I was trying to do a double IPA for 8.8% IOG: 1.08 but ended up with 1.06. I even did a reiterated mash which I thought was almost fool proof...Also did an iodine test which turns out doesn't mean what I thought it meant (realise now it's about starch conversion, but that starch has to be adequately released first for the test to matter). Anyway, here are the things I have tried and still getting terrible efficiency:

Stirring Mash - every 15 mins or so

Mash time - 60-70 mins + mashout

Grind - grind my own grain and have a bit of flour, can't grind much finer. I do need to get a feeler gauge though to ensure it's the same measure each time.

Water ratio - have increased this from earlier to 3.5l/kg

Mash Acidity - High - corrected down to 5.2-5.3ph

Hot Sparge - Yes

Iodine test - Yes (never ends up black after 40 mins)

Water - generally add a small amount of calcium chloride

Any other considerations would be great.

  • Assuming you are taking temperatures of your mash, what temperature are you aiming for? What temperature does your thermometer read? If it isn't a super-spiffy expensive thermometer, have you calibrated it properly? If not, fill a glass with water and ice. Your thermometer should read between 32F-33F (0 Celsius).
    – Scott
    Mar 7, 2019 at 6:40

3 Answers 3


Are you confident that your recipe design calculations are correct? Are you confident that your grain specs are right and that the grain is of adequate quality? All of the measures you have taken should get you pretty good conversion efficiency, so I would start investigating your lauter efficiency and your grain quality. I would also double check (if you haven't already) the accuracy of your scales and your volume measurements.

Can you tell me how you design your recipe, and what efficiency you calculate for?

To give you a comparison, I usually mash for 60 minutes and would stir maybe twice excluding dough in, I uusually adjust my ph to be spot on, but not always. I'm always between 5.2 and 5.8 though. I mashout at 78 celsius, and sparge at the same temperature. I grind my own grain (unknown gap, but all kernels are split, and there's a little flour). I acidify my sparge water with lactic acid down to about the same ph as the mash. I usually get 82-92% efficiency this way. My brew length is 50L

  • Fairly confident on the questions in the first para. I use beersmith with a profile for robobrew. Recipes set up for 70% mash efficiency. I have not thought about acidifying the sparge water so I might give that a go. Another thing I have been lax with is measuring and will rectify next is measurement of the water - my default is to fill the robobrew to the right amount for strike water and then just sparge until I get pre-boil level (usually 28-29L to boil down to 24-25L).
    – W4K1NG
    Mar 3, 2019 at 1:13
  • @W4K1NG While 70% seems to be a good efficiency factor based on the three recipes in your linked original post, I'm not surprised it gave you a low gravity on the double IPA you mention above, its OG (1.080) being a full 45% higher than the highest of the three previous recipes (1.055). On any system you'll see a good correlation between rising OG and falling efficiency (given a fixed pre-boil volume). Mar 3, 2019 at 16:27
  • I second Franklin's comment. I'd still counsel taking the measurements though. One approach for high gravity beers, if you can't get the efficiency up in your robobrew, is to either partigyle a few times, or mash for a weaker beer and make up the gravity with an appropriate extract after lautering.
    – Frazbro
    Mar 4, 2019 at 0:01
  • Re-checked the beersmith profiles etc. for the DIPA. It was set to a different profile (doh!). Brewhouse efficiency was set a tad high and therefore mash efficiency. With this adjusted I'm still undershooting but not as far off. I will adjust my mill using feeler guages and try acidifying the sparge water next time and report back. Cheers
    – W4K1NG
    Mar 5, 2019 at 8:47

I suspect that your robobrew (relatively) sucks at the mash. I have a few different mash vessels and I get different efficiency from the square cooler than the nice round Igloo. The Igloo does a fantastic job 80+ percent, the square one 65-70 percent.

Grain can also get you. My mill is set to run a standard 2 row malt. I get Marris Otter and the grains are smaller, so they don't completely get crushed like the 2 row. I get a little less efficiency (meh).

In general I think your robobrew is just fine. Adjust your brew to match the efficiency you are getting and add $1.50 more grain to even it out... If you really really want more efficiency then crush the grain a little more, if it's not a stuck mash then it will be just fine.

Most of all, keep brewing and don't worry so much. I think Denny Conn said it best "Grain wants to be turned into beer". I think it's our job to help it along.


I wanted to give an update. I got feeler gauges and crushed at 0.83mm. This was a little too fine, but resulted in a reasonable conversion efficiency of ~73%. I also mashed with a little less water and sparged with more. Stirred my mash vigorously and frequently as well as sparging slower. Next time I will crush at slightly higher and hopefully achieve around 70% again.

Thanks for your help.

  • 70% is just fine. Keep up the good work!
    – Pale Ale
    Apr 1, 2019 at 12:18

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