Before moving into the wet versus dry milling debate, I should explain what I'm talking about.Normally when one mills grain before mashing, the grain is dry and when the barley gets milled, the husk gets torn up because it is fairly papery in texture. You can condition the grain by spraying it down. Usually I see homebrewers doing this by tossing it in a garbage bag and spraying the grain with a small amount of water from a soaker hose and moving the grain from one side of the bag to the other so it gets evenly wet. (I found this, more descriptive explanation on another website but you can google for other brewers' processes.) You don't want to soak the grain. It should only soak the husk but the actual seed inside should remain mostly dry. The effect of this soaking just prior to milling is that the husk becomes more pliable and tears apart less. The seed still gets milled the same but the husks stay intact better. As a result, you should get a better filtering effect during lautering. Obviously, for BIAB brewers, employing this technique may be less valuable because you are relying on the bag to act as your filter.
Ok, so you can see how brewers using a mash tun set up would benefit from an improved filtering from wet milling. The article confirms that wet milling increases the speed at which lautering occurs. It didn't speak to whether it made milling any faster but a key point made is that the pliability of the husk allowed grain to more easily and evenly mill through a two-roller mill and produce similar crush as a six-roller mill on dry grain. For brewers like myself using corona mills, that is an enticing idea. I am not entirely in love with the crush I get from my corona mill, although I accept its results, so conditioning the malt may be a good way to improve my relationship with my corona mill even if it doesn't save any time on brew day. That's a win for wet milling.
The article goes on to identify that wet milling resulted in a higher level of protein in the wort than dry milling. The article did not identify why there was a difference but posited the increase was a result of either more efficient mashing or improved filtration. I'm not sure I understand either of those premises, nor did the article attempt to explain why, but the article did point out that elevated protein levels are not always a benefit. Sure, if you have a wheat-forward beer it's not bad to have lots of protein and protein will help put body into a brett beer (protein is one of the few things brett generally doesn't metabolize well). In lower levels it is good for foam stability and some body. In high levels it adds haze and results in a lot of trub. This could be a win or a loss. Depending on how much protein you are getting, it may improve things about your beer that you currently find missing or it may create problems you didn't have before.
Another difference identified in the article is varied levels of ferulic acid and other phenolic compounds. Ferulic acid is a precursor to the clove flavor in weiss beer. Phenolic flavors can be pleasant when they bring earthy spice flavors like clove and nutmeg. Not so much when they are medicinal or fecal. The article suggests the wet-milled grain produced a wort lower in phenolic compounds and that result is likely due to keeping the husk more intact because the husk is the primary contributor of phenolics from the grain. Less exposure to the phenolic compounds inside the husk made their extraction less efficient. Again, this could be a win or a loss. For wheat beers in particular, both wit and weiss, that clovey character is a desired product so wet milling may not be advantageous. On the other hand, most other beers do not benefit from phenolic flavors so reducing the phenols can produce a cleaner beer.
For most beers, wet-milling is likely a good candidate for improved control over flavor and body. It seems particularly valuable for brewing lagers due to the ability to reduce phenols in the beer. The increased protein can be dropped out with finings and lagering. Probably also a good candidate for beers with a lot of rye or adjuncts in the mash due to the improved lautering ability. I'm sold on the idea, at least to try it out. I'll probably give it a whirl on the next beer or two.
Do you wet mill? Have you wet milled in the past? What is your experience?