Whisky 'machinery' - the Malt Mill

A new series looking at some of the 'machinery' used in a distillery to create whisky - this time the Malt Mill.

Glen Moray's Porteus Malt Mill

I've covered the basic process of creating whisky here, but I'm going to explore the machinery a little more in this series.

Put simply a Malt Mill crushes the dry barley into a grist ready for mashing where the fermentable sugars can be released; but there is a little more to it than that, it is critical to get the consistency of the ground barley exactly right!

Before a mash can be started the barley has to be milled, usually it's transported from the Malt Bins via conveyor through a dresser, a de-stoner and malt-weigher into the top of a Malt Mill. 

A dresser is a revolving drum fitted with wire mesh, which catches any extraneous items such as pieces of straw and small stones, magnets are fitted to catch any possible metal items. A destoner, effectively a tray or sieve set at an angle, propels the malt forward to the next stage, while any stones pass to the rear of the unit and are caught in a mesh. Sometimes these are combined into one machine, I think it looks a little like a Robin Reliant!

Finally the malt-weigher allows the Mashman to weight the amount of barley he needs for his Mash, normally by counting the number of full hoppers that go into the Mill. For Glen Scotia that is 70 hoppers, each of 40kgs, giving 2.8 tonnes of grist ready for mashing.

Hopper counter on the right

There are two main types of Mill - a Roller Mill and a Hammer Mill

Roller Mill

Inside the Mill, the barley is crushed by two sets of rollers. The first cracks open the malted barley's thick outer case and the second, adjustable pair, grind the grist to the consistency required.

Hammer Mill

Ian Palmer of InchDairnie distillery explained to me how they work:

"The malt is transferred to a pre grind hopper above the mill. The hopper is also the weigher. Air is drawn thorough the mill and into the grist case. The malt is fed into the steam of air via a rotary valve. The air and malt mixture passes into the mill where the malt is struck by a row of fast rotating hammers. The malt breaks up into small pieces. The air and now grist mixture passes through a small screen where any particles that are too big are caught and these are then brought back round and struck with the hammers again until small enough to pass through the screen. The grist and air mixture is drawn up into the grist case where the air is filtered and passes to the outside of the grist case. The whole process works under a negative pressure."

Milling

Milling creates lots of dust, and as this is combustible a stone or piece of metal striking the rollers could create a spark that would cause the dust to combust. Strict preventative measures are in place dust extraction units and the elimination of any ignition source.

You can see the Roller Mill below is set at 3.5 but this can be adjusted depending on the barley. It takes between two and four hours to grind ten tonnes of barley.

Coming out of the bottom of the Roller Mill, the grist consists of of three parts, each distillery having its own ratios but usually somewhere near 70% grits, 20% husks and 10% flour. You'll usually be shown an example of this when you visit a distillery - a Shuttle Box, which sieves the milled product into its constituent size categories. Sometimes the Shuttle Box will have a diagram of the Mill.

Hammer Mills creates a much finer grist than a traditional Roller Mill, you can see from the photo below from InchDairnie Distillery, The husks aren't required to form a filter bed on the bottom of the Mash Tun:

This would cause issues in a normal Mash Tun as the fine grist would pass through the plates and block the wort cooler so a piece of equipment called a Mash Filter in tandem with a Mash Conversion Vessel are used - but more about them in the Mash Tun article.

Who makes the Mills?

There are a number of manufacturers of Malt Mill, most distilleries have one. Most have been in use for 50+ years. Two examples you are likely to come across are Porteus and Robert Boby but there are others:

Porteus 

It has been very difficult to find out much about the history of Porteus but what I could find was that George Porteus & Sons were manufacturers of plant for the brewing and malting industry, and for seed milling, at Leeds Bridge Works in Leeds. It looked like they started sometime in the late 1800's.

The brewery and malting side of the business made machinery for the 'dry' side of breweries, this included the conveyor equipment for the malt, and Malt Mills. Theakston's Masham brewery had a Porteus Mill installed in 1913. Craigellachie Distillery claim their Mill dates back to 1860s but I think they mean 1960's. 

In 1966 Dawson and Barfos acquired George Porteus & Sons before they themselves were bought by Richard Sizer of Hull - some name plates say Leeds, others say Hull. Some plates say Porteus, some say Richard Sizer's Porteus. Bowmore have a Porteus (Leeds) Mill and Sizer feeder. Tomatin's Mill is from Hull.

Briggs of Burton acquired Richard Sizer in 1993 and the building of Malt Mills stopped.

Porteus Malt Mills in use at Craigellachie, Glenlivet, Springbank, Bunnahabhain, Shizuoka (Japan) and Glencadam:

Robert Boby

Robert Boby was born at Stanford in Norfolk 1814. He moved to Bury St Edmunds in 1827 and in 1830 joined the Ironmongery business of Mr William Groom, as an Assistant. He became Groom's partner, and took over the business when Groom died in 1843.

In 1855 Boby was approached by Thomas Cooper Bridgman, a chemist also from Bury St Edmunds, who had been granted a patent for the Construction of screens, riddles, or sieves. Together they built a prototype corn dressing machine - these proved to be very popular and by 1887 they would sell over 13,000 units all over the world. The successful business boomed at the St Andrews Ironworks making agricultural implements, screening and dressing machines, hay makers, horse rakes, and brewers' or maltsters' plant at one time employing up to 200 people.

In 1883 Boby was made the Mayor of Bury St Edmunds, he died in 1886 aged 72.

After Robert's death his nephew, Charles Edward Mumford, took over the at the ironworks and in 1877, following a disastrous fire, he rebuilt all of the factory, including a new main office and showroom. In 1898 Mumford created a new company of Robert Boby Limited. A new Foundry was built in 1900 and the company had expanded to employ 300 people.

In 1913 Boby's had joined forces with J. A. Topf and Soehne, German malting engineers, to build their advanced equipment in the UK. Boby's had also obtained the rights to manufacture the "Galland" malting drum, which they would develop and improve as a means to produce green malt. Developments like these would gradually cause the demise of the much older floor malting process.

During the War Boby's won some subcontracts from Vickers Engineering to produce weapons and tools for the Government including minesweeping equipment. In 1927 Vickers bought out Robert Boby Limited,  the company continued using it's own name, but with the worldwide depression all manufacturers were experiencing reduced orders they attempted to sell off the Boby works but there were no takers, many of the workers at Boby's were laid off as orders dried up.

It wasn't until the start of World War 2 that work started to build up again, more military work. Following the end of the War business boomed with Boby's continuing to produce seed and grain cleaning machinery, malting and brewing machinery, pneumatic intake plants and mechanical handling equipment. A lot of the equipment in the rebuilding of the nearby Greene King Brewery came from Boby's. In 1961 Scottish Malt Distillers commissioned four drum maltings for distilleries in Morayshire and one on the island of Islay.

By the end of the 1960's the call for cast iron products was declining, their place was taken by alloy castings and mild steel fabrications, which Boby's foundry could not make economically, in 1971 the Robert Boby Ironworks was closed down.

So although you hear a lot of stories about Malt Mills being so good the company went out of business that isn't entirely true, Malt Mills were a small part of Robert Boby's business. As Ian Buxton said "whisky lore rarely let facts get in the way of a good story".

Robert Boby Malt Mills in use at Glen Scotia, Ardbeg, Bruichladdich, Benromach and Puni (Italy):

Vickers

Vickers Ltd took over Robert Boby in 1927, but it continued to use the company's name.  The mills were built at Boby's but some have a slightly different name plate.

Eventually the Robert part of the name was dropped and they were simply called Boby Malting Plant. Manufacturing was moved to the old Supermarine Spitfire assembly plant in Eastleigh near Southampton.

Vickers Ltd Boby Malting Plant in use at Glengyle, Ardmore and Ardnahoe:

Bühler 

Founded in 1860, Bühler is a family business, based in Uzwil, Switzerland, where it manufactures mills for the flour milling industry, they produce both Roller and Hammer mills. Jura distillery uses a Porteus Mill but have a Bühler weighing scale to feed in the barley.

Bühler roller Malt Mills in use at Glenfarclas and Auchroisk and a more modern simpler one at Kingsbarns:

Glenlivet use a Bühler Maltomat 2, Allt-A-Bhainne use a 7 roller Bühler.

Bühler hammer Malt Mill in use at James Sedgwick (South Africa) where it's dual functional, used to grind both grain & barley:

CTS Process

Formed in 2011 by four engineers, three of which were apprentices with Richard Sizer Limited (who took over George Porteus and Sons Ltd of Leeds) in the 1970s. Based just north of Hull, Cottingham Technical Services supply mechanical handling and cereals processing equipment to the brewing and distilling industry.

CTS Malt Mills in use at Aberagie, Lindores, Lakes (England) and Yuza (Japan):

 

AR Engineering

Based in the same town that Robert Boby's factory used to be in, Bury St. Edmonds in Suffolk, and in fact only 15 miles from where that factory was is Alan Ruddock Engineering. They are the UK’s leading manufacturer of precision mills, specifically designed for the brewing and distilling industries having been in business for the last 50 years.

As you can imagine it's quite hard to get hold of an old Porteus or Boby malt mill these days so more recent distilleries, or those replacing unrepairable equipment, are using newer technology such as that from AR Engineering. For example the AR 2000/300/2 used at St. Georges is a two roll mill with a milling capacity of one tonne per hour. The rolls are manufactured from high grade induction hardened steel. The roll gap can be set within 0.05 mm by use of the positive drive analogue dials.

AR2000 in use at Wolfburn, Edradour, Cotswolds, St. Georges, Lancaster Spirits Co. and Arran:

Photo: Sarah Hardwick

Asnong 

Asnong Brewery Services, is a Dutch company founded in 2011, which specialises in raw material handling and fine milling technology for the brewing industry. An offshoot of  Asnong Belgium who have been producing hammer mills for over 70 years. Again some newer distilleries have gone down this route and use a Hammer Mill from Asnong.

An Asnong hammer mill is use at InchDairnie:

Meura 

Meura manufacture Mash Filters, used in some distilleries instead of Mash Tuns, these use 100% flour rather than the normal ratio of 70% grits, 20% husks and 10% flour, so the barley is hammered into flour using a hammer mill.

Meura hammer mill in use at Teaninich:

Maltsters

Some of the smaller, newer distilleries have their barley delivered from the Maltster cracked to their specification e.g. Bimber, they could use any of the Malt Mills mentioned above.

Bimber barley pre and post cracking

Maintenance

In his book Whisky Galore, Ian Buxton writes about how he saw "a metal plaque with the name of Ronnie Lee on a mill at one distillery. He’s told that this is the name of the man who does the maintenance on the mill. Then he sees the name again at another distillery, and his enquiring mind leads him to arrange a meeting with Ronnie Lee at his factory in Hull. Lee turns out to be a former weightlifter who’s now responsible for keeping many a distillery mill running."

Ronnie Lee, the Man who Mends the Mills. Photo: Ian Buxton.

Next Step

Once milled a batch of many tonnes of grist is ready for mashing in the Mash Tun.