Where to measure mash temp

[SG9090]

Hi,
I brew on a 3v system and wondering where the actual mash temp can be assumed to be measured from. My HLT is of cause temp controlled and the water is pumped around it for temperature consistency. I have a thermometer in the mash tun and my mash tun dose have an insulation wrap around it. At mash in the tun measures the same as the HLT however after 10 min the tun drops a few degrees end on mash the difference is about 4 degrees.
So when HLT says 66 deg and mash tun says 62 deg at the end on the mash, what can I assume my mash temp is.

 

[Moad]

Your mash temp will drop after you dough in. If your pump is controlled by mash temp to recirc through the HLT I think it would be best to measure in the MT.

If you constantly recirculate you would measure at the return and control the temp of the HLT to regulate Mash temp.

 

[SG9090]

I have two pumps one recirculates the water in the HLT and one pump to recirculate the wort through the herms.

 

[Moad]

So you aren't exchanging heat in the MT, you aren't able to increase the heat in the MT somehow? If not, measuring the HLT is pointless, measure the MT

 

[Kingy]

If you have your herms coil in your hlt id have a 'T'piece on the outlet of the coil with a probe to measure and regulate the temp from there.

 

[SG9090]

The heat exchange is in the HTL and the HLT has correct temp, so i assume the wort is at the correct mash temp when leaving the HLT but then it's running into the top of the mash tun, where the temp says it's a few degrees less, the mash tun us a 50l keg whith the temp probe about a quarter the way up from bottom. I've checked the HLT and mash tun temperatures and happy both are correct.
So my question is where do a measure the mash temp from?

 

[TheWiggman]

I'm gonna be blatantly obvious here - mash temp should be measured in the mash. Anyone doing HERMS or similar should do the same. The control temp (whatever you want the mash to be) should be measured at the coil out coming from your HLT as there is no guarantee it's going to be the same as the HLT temp. It will always be equal to or lower than the HLT temp. Moreover, your control temp shouldn't exceed your rest temp even though the mash tun temp will lag.
This sticking point is where some thought needs to go into recipes and individual systems. The mash temp will always lag the control temp because you are not instantaneously heating the entire mash tun. This means that conversion will be occurring slightly differently in the mash to the coil out, and depending on your ramp speed and flow rate you may not get the results you expect compared to someone doing infusion mashing. Brew, check results, take them into consideration and brew again.
So even though mash temp should be measured in the mash, what you really need to think about is what you're trying to achieve (namely attenuation / FG) and learn how to go about it with the limitations of your system.

 

[Yob]

I'm gonna be blatantly obvious here - mash temp should be measured in the mash.

no..

.. ALWAYS ... measure at the coil (HERMS/RIMS) outlet, this is where the highest temperature is... if you measure at the mash you may well be denaturing in the coil.

 

[TheWiggman]

You're misunderstanding me. I said control temp shouldn't exceed the rest temp. The rest temp being 56 - 65 - 72 etc. The mash temp is literally the temp of the mash, which lags the rest temp.
Ed: I'll elaborate (with semantics because I think it matters). You said always measure at the coil out but it's more correct to say control at the coil out. Rest temp should be set there. But I reckon measure the mash itself on occasion to get a feel for what's going on, especially with a new system. I'll step from say 55 > 64 and by the time I've got 64°C coming out of the coil the mash is at 61°C. Over the next 10 mins it'll go to 63, and 10 mins later 64°C. Now when I had lower flow rates because I was getting a stuck braid, the mash was lagging much more and resulted in some low attenuation but I couldn't work out why.
Hence if I'm after a certain attenuation, I'll go by history of my system rather than 'they rested at 66 therefore I should too' if you catch my drift.