Decided to reply to AndrewQld in this thread, should be more appropriate.
I really don't see the logic there, are you saying that there are no starches in the grain bed to convert? I'd be a bit worried about missing out on some of those starches and enzymes.
As it was explained to me Andrew, solubilised starches are washed out of the grainbed and away with the liquor where it is heated on circulation through the HE then returned at or a little below the HE controllers set temp. After 10 min or so of contact with liquor most of the available starches in the grist should have solubilised into the liquor, none or effectively none, of what we want would then be present in the grist.
And another point, If the temp in your grain bed is lagging so far behind the wort that is circulating through your herms then it means your not circulating through your grain bed very effectively and you are more than likely channeling the wort down the sides of the tun and not through the grain bed which would be why your temps are so different.
After having a conversation with Gregs on Saturday about this issue I decided to test the theory myself, I did a fairly simple brew of a lite lager and added a good does of rice hulls to the grist to aid the flow, I kept my recirc at the usual flow rate. The grain bed lagged by about 2 during temp changes but settled at the correct temp within about 5 minutes. I also noticed that throughout the mash the grain bed was soft and not compacting at all, the rice hulls helped here and also a balanced recirculation speed.
I recirc very slowly so as not to compact the mash, my mash remains very open and floating, never need hulls even at 60% wheat.
When I have brewed without rice hulls I've noticed what you and Screwy report, a big difference between the grain bed temp and wort out temp that can take a long time to even out unless the mash is stirred, then it seems to even out pretty quickly again indicating poor flow through the grain bed.
So it seems that it might be more of an issue with poor circulation through the grain bed that is causing the mash to lag behind the HERMS so much and for so long and it's fairly easy to fix with rice hulls and balancing your circulation speed.
Does that make sense?
Cheers
Andrew
Probably does to you Andrew, from your experience with your system. And I think its as important for HERMS brewers as all AG brewers to realise kit does make a difference, you need to apply the same basic principals while allowing for differences due to equipment and process variations.
Remember I dont stir my mash apart from a few stirs after dough in and a few after ramping to MO. My experience with my system and from advice received is that the temp of the grainbed is insignicant. The max temp reached by the liquor during recirculation is very important. My mash efficiency is very high >90% so I have no concerns regarding poor mash circulation.
Part of the problem with my system reflecting different temperatures to yours could be in the type of through the wall dialface thermometer I am using. Am positive the temperature of the tun surrounding the mounting position bears quite an impact upon the temperature displayed. The reason I believe this is that if I take a temp reading of the wort/liquor inside the tun during recirculation using a good quality thermometer it is much closer (around 2) to the HE out temp of the liquor, but the dialface is way below over quite a long time, indicating that the time taken for the tun to heat up is affecting the reading. My MM dialface thermometer has a thick SS section from the threaded part inside the tun which reduces down to the smaller probe. I have always had this problem with this thermometer, maybe the large section sinks temp away from the probe affecting the reading. Well before changing to HERMS I was having attenuation problems. Having to mash at much lower temperatures than convention would dictate to achieve good attenuation would indicate there was an anomaly in temperature reading somewhere.
Cheers,
Screwy
