Beerisyummy said:
If it's a centrifugal type pump any restriction will reduce the load on the motor. The speed of rotation increases and power consumption goes down until you get cavitation.
Some restriction is a good thing. IME the sweet spot is usually between 60- 90% of rated flow.
FB,
I'm not sure what my mill gap is exactly, but I have opened it right up to the point where it just pops the husk open. This gap gets changed slightly sometimes for different grain types. After trying several different gap settings I've found this to be the best gap setting for flow and efficiency.
It looks something like this most of the time. (3:2 Wheat
ils in this shot).
P5165226.JPG
Your mash seam gas problem sounds pretty interesting. I'm guessing there must be a pocket of air getting trapped under the false bottom when you fill the MT.
Do you add water to your grist, or the other way around?
Water goes into the grist. I don't underlet as I tried it a few times before everything was hard plumbed and it didn't change things. I do stir like buggery once full volume is achieved and don't recirc during the 52 degree rest.
Camo6 said:
FB I'm keen to see if you can solve this as it's been happening to me occassionally with my system. While getting ready to sparge I'll get a few bubbles rise through the mash which loosens it and it then swells as I fly sparge. This makes it difficult to maintain enough water on top of the mash and I seem to get more crud into the kettle.
I suspect on mine it's a pocket of air which is forced back through the mash by the gravity of the herms coil contents or a qd sucking in air. Maybe it's to do with the order I close and open taps or switch off pumps. It doesn't happen all the time but I haven't changed my mill crush in that whole time and use minimal adjuncts.
Fwiw I think my crush was set to about 1.1mm. I use a kaixin pump and recirc the mash slowly for a minute or so then run flatout for the entire mash. Only stuck sparge was from a 20% rye grist.
This sounds exactly like what I was getting with the LBP. Sometimes it was happening with the pump still running as the temp approaced mash out, although it hasn't happened like that with the big pump. I guess it's pulling too much vacuum to let the air rise.
TheWiggman said:
Fat *******, if air is coming out it must be trapped in a fitting somewhere. Can you run the flow backwards? Do this prior to starting your mash and this might blow out any air that could piss you off later.
Alternatively, you could try one thing I do once the system is flowing and ready for heating.
- Turn off recirc pump
- Put your lips around the mash return line
- Blow hard
Obviously don't blow air all the way back to the MLT.
I find this sometimes gets air pockets out of the tee fitting in the MLT. Otherwise, why don't you just change from recirculate to lauter/sparge prior to adding your grain?
Don't think there is any air trapped in the system. The outlet of the MLT drops about a foot to the pump. The wort return bubbles like buggery when you open the tap! Stranger things have happened though, and this is probably something to check out.
mb-squared said:
FB, I've gone back over your brew rig thread but didn't notice anything about your false bottom. What are you using there? Does it cover most of the bottom of your MT? The channelling that you've mentioned suggests that something is amiss with your false bottom. Then as for the grain bed springing up, I just find this very hard to believe, but perhaps it is related to the false bottom problem. First, are you sure that it isn't just the hulls floating to the top? If it is the whole grain bed, and you don't notice any air bubbles in your recirc lines during the mash, then that suggests you do have a trapped air pocket in there somewhere that the recirculating wort is bypassing during the mash -- again, only possible IMO with a very faulty false bottom.
I don't know anything about fluid dynamics, but I notice that your MT is about as wide as it is tall. I hope this isn't the source of your problem, but I notice that the pots you can buy for this purpose (e.g. blichman or spike brewing) are taller than they are wide. Perhaps that is important? Sorry can't be of more help! I hope you're able to get it sorted.
The FB is a domed circular thing from Beer Belly which is about an inch away from the wall of the pot. I've never had channelling with it previously, nor on the only other time I used the big pump a couple of weeks ago. The only things that have changed is the bigger pump and the finer crush. The grain bed springing up as a unified mass happened when I didn't use rice hulls, which are something I don't like using unless absolutely necessary.
booargy said:
are you sure it is air and not a surge of liquid as the vacuum caused by the pump is released? also try cutting the grain bed without disturbing the base using a long knife before sparge.
Probably a combination of the two. Trapped air plus surge = lifting mash.
Beerisyummy said:
How much of a vacuum do you guys get? I always thought you were meant to balance the flow so it didn't compact the grain bed.
Centrifuge pumps are also meant to push fluids, not pull. Too much of a vacuum and they start making that crackling sound due to cavitation.
Back to the air pocket, I've noticed that my grain tends to expel trapped air bubbles for several minutes. Bear in mind that the recirculation is flowing up through the mash at that stage ( these days, at least). Prior to this I can remember there always being a tiny amount of air trapped under the false bottom.
One can easily imagine how all those tiny bubbles would collect under a large domed false bottom, especially if a pump was really sucking on an inlet at the bottom of a mash tun. Letting the mash stand for a few minutes before recirculation would probably help.
I always let the mash stand for the 10 minute/52 degree rest, and stir to make sure it's all soupy and not dough-bally.
TheWiggman said:
I've heard conflicting advice beerisyummy and I've heard warnings against compacting the grain bed (but mainly to avoid stuck mash). Mb^2 on the other hand goes flat stick with his recirc flow and gets excellent results with efficiency. Until I see some tests I'm unconvinced either way
I've found the vacuum of those pumps to be pretty high. I've only used the kiaxin and LBP but both seemed to pull a fair bit with a stuck mash. .
Heh. When I was doing a hybrid BIAB recirc thing, the LBP once pulled such a vacuum it actually bent the perforated bag rest thing I'd made to keep the bag off the element. It was made from 2mm thick perf plate!
Thanks for all the replies. The current mash regime is as follows.
Heat strike water in HLT.
Put milled grain into MLT
Pump hot water onto grain to acheive 52c
Stir
Wait 10 minutes
Start recirc pump and commence ramp to 62
Continue recirculating through 62/10, 66/45, 72/10, 78/10
set valves to lauter & fly sparge into kettle
Now previously, with the LBP, I'd have problems with the grain bed lifting at either the lauter or during the mash out stage. I did experiment with stirring halfway through the mash which seemed to help, but defeats the purpose of having a recirculating system. I still think it's a function of the crush size. At 1.6mm, there's a lot of whole looking grains, with intact husks that fall to bits when you touch them. I wouldn't be surprised if there was air trapped between the grain and husk. Of course when I milled the grain finer, the husks got ripped up smaller which stopped the air from being trapped there, but it also didn't allow the wort anywhere to travel through, resulting in the stuck mash.
Of course, i'll investigate the air pocket theories, but I think I'll also split the difference between crushes and go for a 1.4mm crush next time and see how that goes.
Cheers,
FB
