RIMS/HERMS time wort spends in the heater vs. the grain

[The-Engineer-That-Brews]

I’ve been asking myself this question recently so as to understand which part of the system is more important when it comes to determining the mash temp.
Having made some measurements of my setup today I can say that each time around the recirculation loop, a millilitre of wort spends roughly:

• 10 sec in the HERMS heat exchanger
• 5 min trickling down through the grain
• 1 minute in the sump of the mash tun

Your system will vary but you can probably say that, while recirculating, the wort spends about 80% of its time in the grain-bed. So (surprise surprise) it’s the temperature of the grain that matters. Equally, if you want to reduce the step time by taking your heater a degree or so higher than the target temp then it’s unlikely to do too much damage to the enzymes.

Hardly startling news - but useful to have confirmed it

 

[The-Engineer-That-Brews]

Another interesting point from this is the non-trivial amount of time that the wort spends in the sump of the mash tun. This is typically a degree or two cooler than the main body of the mash (especially near the start of a rest).
This could be quite useful, because it means that during the alpha amylase rest the complex sugars can trickle down into a relatively cooler zone where there is still likely to be some beta amylase activity able to break them down into maltose.

 

[Buffers brewery]

Interesting. When I put my mash tun/HERMS together I fitted a digital (cheapy from Amazon) thermometer to the wall of the mash tun about 10 cm up from to bottom and another in the wort feed pipe (the bit that moves backwards and forwards) from the HERMS tank above the grain. Setting the HERMS tank temperature and leaving it until everything becomes “constant” indicated temperature “differences” so I could set the HERMS to achieve mash temperature. I avoided bumping up the HERMS set temperature to make things quicker cos I was worried about upsetting the enzyme action.

 

[hoppyscotty]

Just got myself a RIMS setup and sussing it out before using it so got a few silly newbie questions relating to this. Firstly on the enzymes, do they reside in the wort or the grain? I always imagined you're soaking the grain, the enzymes within the grain do the conversion and the resulting sugars are flushed out of the grain husks by the recurulation rather than the sugar and enzymes all residing in the wort and everything happening in the wort. I guess if the enzymes remain in the grain (largely) then the temp of the wort in the HERMS or RIMS section doesn't matter as long as it is the correct temperature by the time it is dumped onto the grain again.

Also how do you control the flow rate through the HERMS/RIMS? do you have something that either turns the pump on and off or varies the speed of the pump or do you just throttle the pump with a valve and have the pump running 100% for the entire mash. I'm less concerned about the temp control here...the element will turn on and off to manage that depending on the flow rate, but more about matching the flow rate through the HERMS/RIMS and the flow rate of the wort through the grain so you don't empty the dead space under the grain.

Thanks.

 

[The-Engineer-That-Brews]

Those are very GOOD questions in fact :-)

Firstly on the enzymes, do they reside in the wort or the grain?

I asked this question myself recently, and had a very helpful reply from @The Biochemist indicating that they are really soluble, so mostly exist in the wort. My understanding is that during the mash the starches locked up in the grains become dissolved in the wort through the process of gelatinisation (see this excellent article: Starch Conversion - German brewing and more).
However as the wort spends the majority of its time in the grain while your re-circulating, it's the temperature of the grain that you need to target - BUT you want to go fairly carefully because you don't want to overheat it while it's in the RIMS.

I'll come back to you later about controlling the flow rate....

 

[hoppyscotty]

Brill, food for thought. I was tossing up the pro's and cons of HERMS vs RIMS and was worried about this regarding a RIMS system due to the direct contact of the element with the wort and overheating of the wort that comes into direct contact with the element. But there are many RIMS brewers out there who don't seem to suffer any ill effects so either there is no need for me to be concerned about this or its just not an issue.

Look forward to hearing about flow rate control. Thanks.

 

[The-Engineer-That-Brews]

It‘s surprising how much temperature the enzymes can stand, so long as the exposure time is short ;-)

 

[The-Engineer-That-Brews]

I use a HERMS setup so I it’s a bit different, but maybe comparable.
What I do is manage the flow rate to be as high as possible without the pump scavenging (sump running dry due to the flow through the grain not keeping up).
The way I manage the flow rate is not to throttle the pump but to run a bypass on it. IE I have two ‘tee’ pieces: one just before and just after the pump. The ‘arms’ of these are then connected together with a tap. So when the tap is fully shut the full flow of the pump is routed through the recirculation circuit, but as I open the tap, more and more of the flow is diverted through the ‘bypass’ circuit.
The reason I prefer to do it like this is that the flow through the pump itself is always 100%, so it’s less likely to stall or get blocked by bits of crud.

 

[The-Engineer-That-Brews]

Incidentally I just use my counterflow as the heat exchanger:

That’s not quite how I’d normally have it set up but it makes it easier to see what’s going on.

 

[The-Engineer-That-Brews]

And here’s a pic of the bypass on the pump:

 

[hoppyscotty]

Ah that’s a good idea. How do you know when to run the bypass, do you wait till the pump starts to show signs of cavitation/starvation or huddle it from the flow rate?

 

[The-Engineer-That-Brews]

Ah that’s a good idea. How do you know when to run the bypass, do you wait till the pump starts to show signs of cavitation/starvation or huddle it from the flow rate?

I‘ve fitted a sight glass (sort of - just a JG bulkhead with an elbow and a length of translucent 3/8” tubing) to the side of my mash tun, at sump level, so I can see when the level is getting close… I also have a bit of clear pipe on the pump inlet so I can see (and hear!) the bubbles

 

[peebee]

I copied a thread I'd made on another forum >here<. It's followed by some interesting datalogging from someone trying to unravel my work (he "accidentally" supported my work instead!).

Don't know if this "feedback" mechanism will work for you (mini-HLT heater) but it's existance is worth considering. I too thought the mash would be "over-heated" in this scenario, but the (hidden) feedback mechanism counters the potential for this overheating.