Last weekend I tried it. I get considerably less broken hulls, practically whole. Kernel was broken all right. So far so good.

I added 0.5 liter of cold water to six kg of malt by pouring it slowly while stirring malt continuously. Waited about half an hour, stirring it once in a while. I milled it with roller mill.

Sadly, mashing to negative iodine test took not one hour, but two. OK, after one hour solution was free of starch, but stirring still released more of it, while it normally does not, at that point. After 2 hours solution was starch-free even after stir, but I heated to mash-out really slowly, just to be sure. Total time - 3 hours instead of a bit over one.

Overall efficiency was unchanged, 90% of theoretical maximum, perfectly consistent with my usual results - but it took over twice the time. Can there be causation along with correlation, or can I assume it was just a coincidence?

  • Could you go into a bit more detail about your exact process? Did you steep the malt or spray it? If steeped, for how long? Was the water cool or warm? What sort of mill did you use? My guess is that it was just coincidence, but there may be a reason. Oct 6, 2015 at 14:16
  • @FranklinPCombs is this understandable now?
    – Mołot
    Oct 6, 2015 at 14:42
  • The malt may have been too wet, but I don't see how that could affect conversion. I think you may have fallen victim to the vagaries of the iodine test. It's so unreliable that I stopped using it years ago and advise others to skip it, too.
    – Denny Conn
    Oct 6, 2015 at 15:47
  • @DennyConn It's easy to get false negative with iodine test, but false positive? When I see distinct colour change? I doubt it. On the other hand, usual advice is just to stop after an hour, so (if we exclude false positives) would be too soon. I usually do this test only to confirm what I think I know, and this time was different after 1 hour.
    – Mołot
    Oct 6, 2015 at 15:52
  • 1
    Did you check the temperature of the mash after adding the strike water? The strike water will need to heat up the 500g of added water as well as the crushed malt. If your strike water calculation didn't take this into account, your mash temperature could be considerably lower than expected, leading to a longer mash time. For what it's worth, I typically add around 80g of water to 5kg of malt. Just this small increase in moisture content allows me to set my mill rollers to the smallest gap without getting a stuck mash. Oct 7, 2015 at 20:57

1 Answer 1


Brewing textbooks I referred to universally state that the gap between the rollers of the mill needs to be much closer together for wet-milling. You don't mention making any adjustments, so I'll assume you didn't. Since the husk is made more elastic by conditioning, the dangers of pulverizing it with too tight a mill are eliminated, and in fact it may do a better job breaking down the endosperm, which also may have become less friable during conditioning.

This would fit with your experience of a very slow conversion and starch going into solution when the mash is stirred, which could be explained by (counter-intuitively) too large a grind. Or put another way, while wet milling helps the husk hold together, it may also help the starchy parts stick together too, creating a potential issue of over-large endosperm bits which don't easily gelatinize or solubilize.

A few quotes, as mentioned above:

"During [wet] milling they are gently squeezed flat by the large rolls (400mm, 15.75in. diameter; 440rpm, gap 0.30±0.45mm, approx. 0.012± 0.018 in.) of the mill, squeezing out some of their contents." (source)


"[In wet-milling, t]he rollers are closer together than in dry milling (0.35 – 0.45 mm apart)" (source)


"The gap between [the rollers], which may vary from 0.25 and 0.40mm, can be continuously adjusted." (source)

For reference, the same books give ranges between 0.6 and 1.5mm for gap spacing in two-roller mills used with dry malt.

  • "so I'll assume you didn't" - Not adjustment per se, but I do re-set them every time because I unscrew rolls as wide as possible for cleaning after each brew. I think they were narrower. For sure I know endosperm was broken. But when I recall it... yes, it probably wasn't broken enough.
    – Mołot
    Oct 7, 2015 at 13:55

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