Originally Posted by Mateus
If someone could please help me out. Im going to buy a BM clone. I live in Brazil and the manufacture company offers to do a personalized tube to use on the 50L model.
I've been reading this thread and saw the efforts to do high gravity batches. Specially Batfink´s attempts by drilling holes in the tube.
My question would be: what is the most optimized size of a tube (to use on the 50L model) so as to get the higher possible OG?
I ask because it seams its a ratio of grain storage capacity vs. water need to recirculate. Has anyone figured this out?
Tks a lot!
Since I have put a bit of thought into this myself I’ll give you my personal take:
To answer your question, the most optimised size of the tube in order to maximise OG is to make it as large as possible. Reason is that this maximises the ratio of water in direct contact with the grist vs. the total water in the system (however this doesnt improve the OG limitations by very much). The reason why some have suggested using a length in between the short and long pipes is so that you are able to brew a larger volume of wort and then boil this down (to increase the OG) and still have a good (~20L) batch size left over. With the 20L pipe there is just not much wort left. It’s important to note that the BM is limited in post mashing/pre-boil OG… high post-boil OG beers can be easily brewed by increasing the boil length until you hit whatever OG target you are after, no limitation whatsoever here (I did a 155min boil recently to bring a high gravity IIPA from 1.047 post mash OG to 1.083 post boil OG).
The reason why the BM design is limited in terms of post mash/pre-boil OG is because of the large amount of water in the system which is not in direct contact with the grist. In traditional brewing systems there is only the false bottom which can be designed to take up almost negligible space, and then the piping that circulates the wort through the heating elements and back to the top of the grain bed which is also negligible in volume. So almost 100% of the water is in contact. With the BM system there are two areas that take up a significant amount of space; the bottom section of the malt pipe (underneath the mesh), and the space outside of the malt pipe that needs to be filled with water to a certain level to ensure the heating elements are covered and don’t overheat.
These two areas need to be addressed to really make a difference. Since you are doing a DIY BM you could think about doing the following:
- Put the outer heating elements on the inside space within the malt pipe area, you will need less water volume outside of the malt pipe, just enough to ensure the pump does not run dry.
- Reduce the height of the space underneath the lower mesh in the malt pipe. The challenge here is to ensure the water continues to flow uniformly upwards throughout the grain bed, so you might want to add diverters on the pump outlets to ensure this (this is a mod I am planning to try on my BM50L). Alternatively you could just untighten and rotate the malt pipe several times during the mash to ensure uniform flow.
Another more extreme option is to redesign the way the water flows in the system. You could move back to the traditional way of pumping water from the bottom of the kettle, running it up with a pipe and sprinkling it over the grain bed. If you put the heating elements only in the space within the malt pipe underneath the grain bed then you wouldn’t need to utilise the space around the malt pipe at all (bottom of malt pipe would need to be sealed off which should not be a problem). This would be like a typical brewing system however with the amazing benefit the BM has where you can just lift out the grains and boil away in the same kettle. This is how I personally would have designed the system, and might be something I plan to do in the future if I get more free time on my hands.