Modifying a Corona-style Mill

My plan to write some tasting notes for the blog this week was thwarted by a lingering cold that left me unable to taste much of anything.  It hasn't stopped me brewing though, and after a disastrous start to the brewing year (I scorched a hole in my BIAB bag and spilt grain all over the kitchen), I finally feel like I'm getting back in the swing of things.  I have a few interesting batches planned for the next few weeks, and I'm feeling quite excited about how some of the saisons currently going through secondary fermentations in my closets are tasting.  With any luck, in a few months I should have some very nice beer on hand.  I also won a couple more medals in a local competition, which was a pleasant surprise since I didn't expect much from the beers I entered.  I have one beer that I think is very good entered into the Upper Mississippi Mashout next weekend, and I'm curious to see how it does.

One thing that's helped me get back to brewing despite the fact that I've been quite busy is that, after crushing almost 200 batches by hand with my cheap knockoff Corona-style mill, I finally went to the hardware store (a two minute walk from my apartment) and bought the fifty cent bolt I needed to run it with a drill.  The 5/16" bolt screws into where the handle should be, and you can turn it (and thus the plates of the mill) by using a drill with a socket adapter.

Making that first change was pretty easy, but when I crushed the grain for my next batch (a dry stout) I noticed that the crush was pretty uneven, with lots of whole grains visible in the grist.  I went ahead and brewed anyway, but my efficiency took a significant hit: almost 10 points, not something you want to happen with a dry stout, which already risks being too bitter and astringent because of all the hops and roasted grains.  I fermented the batch anyway (it was doing double duty as a starter for a new pitch of Wyeast 1318), and as predicted its tasting a bit harsh.

The problem was pretty obvious: the plates on this kind of mill are often quite wobbly, which means that the gap between them doesn't stay even while you're crushing it.  Usually, when I'm turning it slowly by hand, this isn't too much of a problem, but with the drill turning everything much faster a lot more uncrushed grain was getting through.

There are a couple of modifications you can make to these mills to help prevent the plates wobbling.  I didn't bother with then when I bought it because the crush was OK and I was getting acceptable efficiency, but now I knew I had to try them.  The first is to add a couple of spacers on the adjustment bolts between the two sides of the mill---you can find some good pictures here.  The second is to take out the cotter pin that holds the front plate in place---mine looked like it had been bashed in with a hammer, and took a while to get out---and replace it with a 8/32 inch bolt that will hold the plate firmly in place (see picture).  That was an extra 12 cents, and took all of ten minutes.

After making those modifications, I ran a few handfuls of grain through the mill to see how the crush looked and adjusted the gap until I was happy with it.  Corona-style mills will really tear up the hulls of the grain, and can also produce a lot of flour, but since I'm doing BIAB I don't have to worry about stuck sparges and the like.  I'm also pretty careful about mash pH, which helps reduce tannin-extraction from the grain. There were certainly fewer intact hulls left after using the drill, and a bit more flour too, but I knew I could probably minimize this by conditioning the grain (i.e. spraying it with water) before I crushed it.

Midway through last week I brewed another batch in the evening (a top-up for my pale solera), and crushed all of the grain in the mill. I was a bit worried about my cheap drill overheating and burning out, but it made it through and the grist looked OK, with the crush fairly even and not too much flour (see picture).  I went ahead and brewed, and got an efficiency boost, ending up 3 points over my target O.G.  Today I brewed again---this time a pale bitter---and conditioned the grain a few hours before crushing it.  This seemed to help preserve the hulls more than the first time, when I conditioned it about 12 hours in advance.  And today I hit my target O.G. dead on.

All in all I'm pretty happy with these modifications.  They mean I can crush the grist for my batches in a fraction of the time it used to take me (I'd say about 5 minutes each for these two, where before it would have been more like 30).  I like to crush the grain the night before I brew so that I can get everything going nice and early the next day, but recently I'd been finding that I was often too tired to do this prep, which usually meant that I didn't brew at all.  What's more I have a few high gravity batches planned for the next few weeks, and I always used to dread crushing the grain for that kind of thing---not any more!

I will have to keep any eye on the flavour of my beer---I haven't noticed any astringency from the grain before now, but perhaps the more thorough crush will lead to problems.  I'll also probably need a better drill (I have my eye on this one), but for now I'll keep using my cheap one until it gives up on me.