I'm testing out a brand new 200L system and found a couple of potentially disastrous but potentially easy-to-fix issues:

1) While mashing the temperature indicated on the thermometer which sits near the bottom of the tun was fluctuating wildly between 60 and 70 degrees. It might go from 62 degrees to 70 degrees in a matter of seconds, then a few minutes later fall back down, even without any additional heat from the stove or from hot water additions. Other times when adding heat from the stove the temperature would remain in the low 60s. Obviously this is still in the desirable temperature range for mashing but means it's difficult to control the mash temperature for repeat recipes. There is a sight gauge with an inlet near the bottom and outlet at the top. The tun has no insulation, just a stove for heating/maintaining temperature.

Any ideas what could be going on? Some crazy convection current? At the moment I'm thinking my only option might be to get a jacket to insulate the tun once it's at the desired mash temperature. Anyone have any other suggestions?

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2) My boil kettle is the same size, also with a sight gauge and thermometer near the bottom, as well as an in-place immersion cooler fixed inside. I found that after the boil I cooled for an hour and saw the temperature drop to 20 degrees so began filling the fermenters. However by the time I was drawing the last 3rd of the batch the temperature reading was back up to 50 degrees! Sadly, I didn't realise until I'd already aerated the wort in the fermenter :smack:.

My best guess is that the hot wort rose to the top and sank down to the bottom as I was gradually drawing it off. With less wort in contact with the immersion chiller it wasn't cooled properly. Should I carry on chilling for another hour? Or maybe draw the wort off in batches while continuing to chill? Or plump for a plate chiller?


  • 1
    That looks like one Taobao's finest there! I have a couple questions: 1. Did you recirculate the mash? Stir it much? 2. How thick was the mash? 3. What kind of thermometer? In a temp well or directly contacting the mash? 4. How high is the chiller in the kettle? Was there wort above the chiller?
    – Pepi
    Dec 5, 2014 at 8:58
  • @Pepi 1) I tried for about 15 minutes but noticed it brought the temperature down; I also noticed wort travelling up the sight gauge, effectively recirculating that way; I didn't stir at all 2) The mash was 3L/kg 3) The thermometer sticks directly into the mash via the outlet above the middle of the 3 on the bottom; it's not digital 4) The chiller is about 8cm from the bottom and is about 50cm high; there was wort above it
    – Snowman
    Dec 5, 2014 at 9:31
  • So the cooling issue seems sorted - I recirculated through a pump starting 10 minutes before the end of the boil and continued while cooling. When I drew off the wort this time it was all at 22 degrees - I stuck the fermenters in the freezer for a while to bring it down further before pitching.
    – Snowman
    Dec 8, 2014 at 11:35
  • For the mash temperature I still had a few issues. I tried stirring almost constantly. The reading on the thermometer near the bottom gradually dropped to about 61 degrees over the first 30 minutes. Meanwhile a digital thermometer at the top of the mash read 75 - despite no heat being added and the strike water temperature being only 73. I decided this reading must be inaccurateThe tun has no insulation so I turned the lowest burner (which is really quite weak) on for about 10 minutes then stirred again.
    – Snowman
    Dec 8, 2014 at 12:28
  • this time the temperature reading at the bottom suddenly went from 61 to 85 in about 60 seconds. Basically, I'm baffled as to what's going on. At 40 minutes I gave up - just put the lid on the mash tun and left it. I think my options now are step mashing - heat the strike water to around 62 degrees, mash in, stir, gradually heat to 76 then sparge out.
    – Snowman
    Dec 8, 2014 at 12:28

1 Answer 1

  1. I think stirring is required even if you are running a watery mash with recirculation; you have to at least break up the clumps of dry grain before you can pump it. Heat doesn't seem to move easily through the mash anyways.
  2. Wort that is above the chiller will chill very, very slowly. I find that some wort will also stay hot on the bottom of my pot (on the side opposite my chiller). I think you'd have to drain the wort slowly, or stir it somehow (too risky for me) or modify the chiller to be near the top of the wort.

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