Saturday, 9 March 2013

Going down the slippery slope

I'm in the process of planning a new brewhouse. Yesterday I had people round from the company that's going to build it and the company that's going to install it. Being stuck in an old farm building it's going to be a squeeze fitting everything in so I'm happy to let them play around with the various calculations of vessels sizes and shapes. They've got programmes that do it for you which takes out a lot of the tedium.

But I'm not happy to just accept what they come up with without giving it close scrutiny. Though I haven't got the diagrams yet it was mentioned that the grist case (malt hopper) might be a bit undersized. This would be a right pain as it would mean instead of a single person putting a brew on two will be required, as someone will have to chuck more malt into the grist case as the level goes down. They also said the slope on it will be 60°. This sounds a bit steep to me, and it will cut down the grist case volume, so I've been looking into what angle of slide malted barley has. If I can get away with a less steep slope I can fit in more malt. 

So I've been asking on the internet and looking through text books and old lecture notes. When I was a brewing student one of our first bits of homework was designing a brewery and I know the angle of slide and angle of repose of malt came into it when calculating the size of malt silos.

Eventually in a lecture slide I tracked down what I was after, so for those of you troubled by the vexing question of will my malt slide here's a table taken from Malts and Malting by D E Briggs:

Recommended Min. Slope Angles For Chutes And Hoppers.

Undried, unscreened barley 35°
Dressed, dried barley 33°
Fully steeped barley 45°
Green malt (germinated barley) 45-50°
Malt in culm 40°
Dressed malt 30°
Malt culms (rootlets) 50°
Malt and barley dust and light screenings 60°

The angle of repose of malt is 26° from horizontal and the bulk density is 510-550kg/m3.

It does seem that the plans for my grist case are unnecessarily steep and if it comes in under sized it can be adjusted to give it more volume.


  1. I'd say 60 degrees is correct. As grist is a mix of different sized particles ranging from whole grains to dust it will not behave like malt. If you want your grist case empty without poking it down with a stick you have to treat the whole crush as if it's made up entirely of the fraction with the highest angle of slide eg. “..dust and light screenings 60°”.

    Hope this helps.

  2. I am designing my grist case and trying to find out the angle of repose for milled malt. I did find density for grist but not the angle of repose and I am not sure if it is all that different from un-milled malt (30 degrees, or 26 as you have it). Any ideas? Thanks!

  3. Briggs has it as 26 degrees from the horizontal.