Malting seems to be the one aspect of brewing that most homebrewers are very content to leave to the professionals. Lots of people grown their own hops, and an increasing number of people seem to be taking up yeast culturing. But judging by the dearth of information available online, malting just isn’t that popular.
I do wonder how much of that is just due to gross misinformation about the process. Sure enough, even the few resources out there are riddled with errors sure to doom your batch unless you are rather lucky. I tried to follow some of these and ended up with little to show for it. But now, having made a few successful batches, I hope I can clear some things up. These are the main things that put me off or messed up in the past.
Much of this information comes from three very good sources: Graham Anderson’s article in the Jan-Feb. ’13 issue of BYO, Andrew Lavery’s guide for malting gluten-free grains, and the blog Brewing Beer the Hard Way (where he goes the much further step of growing the grains himself).
Technical aspects and equipment
Malting can be as technical as you want it to be. You can track and control moisture levels and temperatures, or you can be a little more relaxed about it. In my case, I’ve used my fermentation fridge for malting cold-climate grains like wheat (I haven’t done barley yet) but used room temperature for warmer climate grains like popcorn. I haven’t kept track of moisture content, and that may explain some of my undermodified batches that seemed to dry out. However, even those batches have worked out OK for the most part.
Note that I am not saying moisture content and temperature don’t matter. They do, quite significantly. But winging it is often enough when doing this just for fun.
You can go all-out with dedicated equipment, but simple things work, too. I use my apartment’s oven (which has a helpful but not necessary “Keep Warm” setting) as a kiln, which should likewise work for most people. The sprouting bed consists of a large, clean garbage bag on the floor, optionally on a towel to prevent the rather annoying noise if you have wood floors. I use another to loosely cover it up (edit: this may be a bad idea due to condensation and possible mold growth). I have also used baking trays. The only piece of equipment I’ve made especially for it is a rather shoddy oast/tray of folded-over aluminum window screen material. It is flimsy but does the job.
Cleaning and soaking
Graham Anderson’s article suggested repeatedly rinsing out grains until the water runs clear. This seems to work out well. In addition, letting them absorb water without forcing them down is a good idea since some broken grains will float. You definitely don’t want broken grains in your batch, if for nothing else than that they are prone to molding and won’t sprout.
The soaking water should not have chlorine in it. According to at least one malting textbook, it’ll lead to bad flavors in the finished beer, much like brewing with chlorinated water would. I suspect rinsing with chlorinated water would be OK since not much would seep in, but I haven’t tested that yet.
Soaking needs to be broken up so that the grain can breathe a little. Graham’s article suggested 8 hour soaks followed by 8 hour air rests. Three soaks seems to work for wheat and barley, but popcorn at least seems to need four. I rinse the grains before and after each soak. This may well be overkill, but at this scale it is not a problem. It may be possible to use an aeration pump in the soaking water instead of the air rests, but the water should still be changed due to bacterial growth. This is something I am experimenting with right now.
Drying and kilning
This is likely the most important thing that is often wrong, based on what I had read. I certainly had it wrong myself. When malting at home, drying and kilning should be entirely separate processes. Drying under heat is likely to damage your grain’s enzymes since home ovens don’t produce the sort of low, steady temperatures and ventilation necessary for drying. A fan blowing over the grain bed does a great job in a few days (another tip I got from Graham’s article).
Again, grains should only be kilned once they are thoroughly dry. Once the grain weighs less than what I started with, I move part of it to the shoddy oast in the oven where I hold a low temperature (180-200F) with the door cracked open. If your home oven doesn’t go that low, a toaster oven might work (this is another solution using a hot plate in the oven instead of the built-in elements). I kiln for usually an hour to three hours depending on how the aroma and flavor develops.
That last bit is the key: without kilning, malt simply won’t taste or smell like malt. It’ll be extremely pale and likely won’t convert well on its own due to high mash pH, despite its high enzyme content. Sometimes there is a grassy smell, especially if the sprouts were exposed to light, that kilning also seems to take care of. A long boil might do the same.
I let the kilned grains rest for a month or so before brewing. This seems to soften up the flavor a bit, in a good way.
I’m not suggesting that home malting is better in any way than buying it off the shelf. It is likely inferior in pretty much every way, especially predictability and consistency (that’s where being technical really helps). However, malting and brewing with the malts has been the most fun I’ve had brewing since I started doing yeast culturing in earnest. A rich, sweet wort is a lot more impressive when you know the bland, tough and starchy grains that you started with.
Searching through forums, I’ve seen quite a few “why would you want to do that?” responses to people who asked. Frankly, that’s just moronic. You could easily say the same thing about growing hops or yeast, or even about homebrewing in general. These days, there are plenty of good beers at the supermarket, so why bother? Right? Right?
I might at some point post a complete guide of how I do it. In any case, the referenced articles should provide enough of an idea how to do this yourself.