Wed Jun 23, 2010 10:17 pm
If there was an actual difference between the temp of the mash tun probe and the outler probe, then you would expect that to narrow as the mass of the mash heated up over teh course of the brew - as the difference is staying static.. then normally I would say its a calibration difference, but you mention the probes themselves are properly calibrated... so I think its an inbuilt something thats interfering with the probe to cool it down.
Perhaps all teh brass, perhaps not enough wort hitting it.
You could try putting a few ice cubes on the brass outlet and seeng if that changes the reading - and then following up with slowly pouring over some boiling water.
You could also do a run with water only - get someone to stirr the water in the mash tun well while you take some readings... then you know that there is no funny business with the mash and hot spots etc. The temp at your mash tun probe should read the same as the temp at the outlet, and they should both match third (known to be accurate) thermometer your stirrer will be using to monitor the temp of the water in the tun. You need to off-set the one which doesn't match.
If it is that - then really it should be something static that you can offset the readings for - you just might need to be careful, if there are massive differneces in ambient temperature that might effect the "difference level"
What measuring point are you using to control the system?? Thats really the only one you need to worry about anyway, the rest are just ancilliary information.
TB