Corona Grain Mills

Anyone who brews with grains, be it those who steep speciality grains, use a minimash, or use grain entirely will tell you they would never go back to just using extracts alone. But the biggest drawback many will tell you is the cost and freshness of precrushed grains. This is not surprising, as the brew shop has to offset the cost of the mill, and the handling involved in supplying you crushed grain.

Many CraftBrewers will look at the cost of a roller mill, but soon forget it as the cost of an imported roller mill is quite high. But there is an alternative out there that people overlook. It is cheap, very effective and freely available in most countries. The mill is called a Corona Mill.

Corona Mills are designed to crush grains to make flour. They work in a similar way to old fashioned meat mincers. You screw it onto a bench, and you turn the handle that turns a cork screw inside it that pushes whatever is inside out the other side. The difference is that instead of pushing meat through small holes, a Corona Mill pushes the grain between two flat plates, one of which rotates.

Corona mills have gotten a lot of bad press over the years, with claims that they are unsuitable for brewing as the give a very poor crush (i.e. tear the grains rather than squeezing them) leading to flavour and extraction problems. The claims have usually originated from either the manufacturers or owners of the more modern roller mills.

But before roller mills (such as the PhilMill, Valley mill and MaltMill) were available for small-scale brewer, Corona mills were the only ones available. Many brewing books had sections on using and adjusting a Corona type mill. Dave Miller's book from the late 80's had a whole chapter devoted to using and adjusting a Corona mill, and he is often quoted as obtaining extremely high extraction rates from the grain.

There seems to be two distinct types of Corona mills - good ones and bad ones. The good ones are well made with the moving plate being securely fixed to the shaft, and rotating parallel to the fixed plate. Bad ones have a moving plate that either wobbles around or is skewed to one side making it impossible to get a good crush no matter what adjustment you try.

So while it is possible to get a suitable crush for brewing, they do have one major disadvantage. The throughput (flow rate) is very low. Yet Corona Mills can be motorised very easily, and will crush between 1 to 2 kilograms of grain per minute.

The obvious way to motorise is to fix a drill onto the shaft. This works fine, and will give you a quicker through-put and satisfactory crush. The disadvantage of drills is that they may spin the shaft too fast, spraying the grain everywhere. Also you have to set up the Corona Mill and drill every time you do a brew.

Here is a set up from Graham that is more permanent, spins the shaft at a much slower speed, and is basically "set and forget".

The mill here is set on its own stand. It is on wheels so that it can be rolled about. The motor at the bottom came off an old cement mixer. This type of motor is ideal, as it has a lot of power at low revolutions. You will have to adjust the mill speed by altering the size of the flywheel on the mill. This will depend on the size of the motor that you use.

The belt itself is quite loose. You should note that when fixing belts to flywheels, the belt should grab the flywheel. You should not rely on the belt being tight as you can get it to turn the flywheel. If you do that you will wear out the housing on the shaft.

The switch for the motor is at the front.

David's mill has a similar construction. The Corona mill has been bolted to a welded frame, and this allows the mill to be moved to give the correct belt tension. The motor and belt is from an old washing machine, the stainless chute was cut from the inside of an old dishwasher, leaving only the pulley to buy.

The frame was built to allow a plastic bucket to sit under the stainless grain chute, but does allow a fair bit of 'dust' to be emitted. To totally eliminate any dust being produced an old grain bag is used instead of the bucket, with the top of the bag being pulled up over the top of the mill.

So what is the cost?

The mill costs about (Australian) $60.00. Flywheel and belt $30.00. Wheels and motor from the dump, $10.00. Timber etc was just lying around the house.

There you have it. A motorised mill for under $100.00. Worth considering!

Shout
David & Graham