You have a couple of major problems as I see it.
Firstly, and possibly most importantly, you are using a centrifugal pump to move mash around. Assuming this has a similar impeller design as a convention beer transfer pump, you will be severely dmaging the grain particles, smashing them up into extremely fine particles, which will contributs to a set bed. I assume you are using a centrifugal pump for both recirculation in the mash heating phases, and also in the mash transfer. You need slow speed pumps - I believe some people have used peristaltic pumps with great success, and these are probably more practical than buying special low speed open impeller pumps.
Secondly, you really don't have enough rakes in the lauter. "Conventional wisdom" is that lauters should have a bit over 1 rake per square metre - which immediately means yours is under raked. However, there is another problem. These figures are valid for large lauters, say 5 metre diameter. This ratio of rakes to surface area allows the raking tracks to be say one inch apart, but without turning the bed. You need more rakes, but because of the small area being unraked at any one time, there is a risk of turning the bed, particularly if the rotation speed is too fast. I seem to remember the stated optimum rake speed gives 12.5 rakes / sq metre / hour.
The flights on the rakes are very steep. You may find this is causing the bed to turn, rather than loosening the bed up. I haven't measured them, but from memory, I have seen somewhere about an angle of 7 - 9 degrees, not what appears to be closer to 30 degrees.
You need to slowly vary the height of the rakes throughout the runoff as well, so the flights do not track at a single level
The liquor to grist ratio is very thin, and means you cannot sparge very much. I suggest you move to something close to 2.5 to 3.0: liquor to grist, and increase the sparge volume.
And the agitator speed may be so high that it is smashing the grain to pieces. The blade needs quite a high surface area but comparatively low peripheral speed.
Hope this helps
Firstly, and possibly most importantly, you are using a centrifugal pump to move mash around. Assuming this has a similar impeller design as a convention beer transfer pump, you will be severely dmaging the grain particles, smashing them up into extremely fine particles, which will contributs to a set bed. I assume you are using a centrifugal pump for both recirculation in the mash heating phases, and also in the mash transfer. You need slow speed pumps - I believe some people have used peristaltic pumps with great success, and these are probably more practical than buying special low speed open impeller pumps.
Secondly, you really don't have enough rakes in the lauter. "Conventional wisdom" is that lauters should have a bit over 1 rake per square metre - which immediately means yours is under raked. However, there is another problem. These figures are valid for large lauters, say 5 metre diameter. This ratio of rakes to surface area allows the raking tracks to be say one inch apart, but without turning the bed. You need more rakes, but because of the small area being unraked at any one time, there is a risk of turning the bed, particularly if the rotation speed is too fast. I seem to remember the stated optimum rake speed gives 12.5 rakes / sq metre / hour.
The flights on the rakes are very steep. You may find this is causing the bed to turn, rather than loosening the bed up. I haven't measured them, but from memory, I have seen somewhere about an angle of 7 - 9 degrees, not what appears to be closer to 30 degrees.
You need to slowly vary the height of the rakes throughout the runoff as well, so the flights do not track at a single level
The liquor to grist ratio is very thin, and means you cannot sparge very much. I suggest you move to something close to 2.5 to 3.0: liquor to grist, and increase the sparge volume.
And the agitator speed may be so high that it is smashing the grain to pieces. The blade needs quite a high surface area but comparatively low peripheral speed.
Hope this helps
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