Two different mash tuns but same crush question PLEASE...

[SB Brewer]

My brewery has been open for 7 years and I have been fighting a problem for over a year. Our first Mash tun is 4 bbl. We dough in using a mash paddle only and then vourlov and sparge etc... A year ago I bought a 2nd system and kept both systems running. The 4bbl mash tun's false bottom has a surface area of 940 square inches. The false bottom on the 12 bbl mash tun has a surface area of 2760 square inches. I made sure to order the same exact sized wedge wire false bottom on both. I even purchased a different sized wedge wired false bottom to see how to solve the problem. The problem is, using the exact same grain crush and exact same grain my 4 bbl gets 90% efficiency and my 12 bbl gets only 65% efficiency. There is two major differences. Small one we use a mash paddle. The 12 bbl we use a rake on a motor. I have tried welding extra pipes under the false bottom to get more escape routes for the grain. I tried slowing the mash down coming out by closing my valve going into the wort grant. I tried rice hulls. I tried welding design changes in multiple ways. Some local guy tells me that it is the grain crush. But I can not see that being the case because the wedge wire bottom and the grain crush are exactly the same made by the same company and everything. Any ideas? Is the rake at fault? I am lost and frustrated for over a year.

[dick murton]

Two main possibilities - the mixer motor and rakes are knocking the air out of the mash so it doesn't float and thus you are liable to end up with a set bed, giving the poor extract, or, far less likely in my opinion, your sparge is not even. This size of tun, a single runoff pipe works fine, so I really don't expect that is the problem.

A bit of work required, but take out the rakes and mash in manually as you do with the smaller tun. I have thrown out the rakes of a couple of commissions because they simply are not designed to mix properly, and know a couple of other people who have done this more times - simply because they have commissioned more new small BHs than I have. If this works better, then get yourself a premasher made up and run down the sidewall of the tun, so save the manual mixing. If you trawl through this site, there are a number of comments (including a couple of lengthy ones of mines it has to be said) about the use of rakes for (non) effective mixing

[KandS_Consulting]

The rakes are not the issue. How is you grist hydrator working? Some imported models do not hydrate at all. Do you underlet the mash? Are you sure your efficiency computations are accurate? Have you considered using Amylase enzyme? What is the geometry of your 12 bbl mash tun?

[Derrick]

My brewery has been open for 7 years and I have been fighting a problem for over a year. Our first Mash tun is 4 bbl. We dough in using a mash paddle only and then vourlov and sparge etc... A year ago I bought a 2nd system and kept both systems running. The 4bbl mash tun's false bottom has a surface area of 940 square inches. The false bottom on the 12 bbl mash tun has a surface area of 2760 square inches. I made sure to order the same exact sized wedge wire false bottom on both. I even purchased a different sized wedge wired false bottom to see how to solve the problem. The problem is, using the exact same grain crush and exact same grain my 4 bbl gets 90% efficiency and my 12 bbl gets only 65% efficiency. There is two major differences. Small one we use a mash paddle. The 12 bbl we use a rake on a motor. I have tried welding extra pipes under the false bottom to get more escape routes for the grain. I tried slowing the mash down coming out by closing my valve going into the wort grant. I tried rice hulls. I tried welding design changes in multiple ways. Some local guy tells me that it is the grain crush. But I can not see that being the case because the wedge wire bottom and the grain crush are exactly the same made by the same company and everything. Any ideas? Is the rake at fault? I am lost and frustrated for over a year.

Hello, if you are using same brewing method, same grain etc. I think the main issue is brewhouse diameter. Because, the brewhouse diameter can influence the spent grain thickness, while the spent grain thickness will influence the lautering efficiency. Finally, it will influence your brewhouse efficiency.
For your 4bbl system, the false bottom surface area is 940 square inches, in calculation, your brewhouse innter diameter around 900mm. It is most standard for brewing 12 plator beer.
But for your 12bbl brewhouse, in calculation, the brewhouse inner diameter around 1500mm. It is wider than standard. If you use less malt, the spent grain is thinner, if you use more malt, the spent grain is thicker. Both will influence lautering effect. The spent grain thickness at 30-40cm is better. So for 12bbl system, you can try to use 290kg to 390kg malt for brewing. And see if it helps.

[Rosie]

Just another thought here. When we moved to our bigger system, I started using the same liquor to grist ratio to mash in and had runoff, clarity and efficiency issues. By mistake one day I added more liquor than I intended at this sorted all our issues. For reference it was going from 2.4l/kg to 2.9l/kg.

[liammckenna]

Consider the depth of mash and the diameter of the vessels. Open surface area on lauter plates one vessel vs. the other and flow rate per unit of open surface area. Also, as Rosie has mentioned, your grist hydration ratios.

Best of luck.

Pax.

Liam