Question about temperature in my mash tun

[NTabb]

I have a BCS-460 that controls my brewstand and I've added 4 thermistor probes. One is a 12" probes that's halfway in the mash tun, one is a 6" probes in the mash tun ball valve(out flow), one's halfway in the HLT and the last one is in the outlet of the heat exchanger. I'm getting a 9 degree difference between the one halfway in the mash and the mash tun outlet which seems like a huge difference. Could there really be a 9 degree difference or is there possibly not enough wort hitting the probe of the ball valve and I'm getting more of an ambient temp? I've added a couple links to some pics below. Any advice would be greatly appreciated. Forgot to mention the probes are calibrated and read the same temp when side by side.

[BrianL]

I'm trying to figure out the same type of problem with my new brewstand. I have a Auberins RTD in a thermowell made from copper tubing in the lid of my blichman boilermaker mash tun. After I doughed in, it it was reading 149, but I used a digital thermometer, which has always been very accurate and it read about 9 degrees higher. I checked the mash in different spots and got a pretty wide range of readings.

I have a thermowell in the ballvalve of my mash tun, and when I recirculated I seemed to get a more accurate temperature.

I think there's something about the grain bed itself where you get alot of pockets of different temperatures if you're not constantly stirring it or recirculating it. Just a theory. If I test with just water all my sensors are right on.

I don't have an answer, but I'm annoyed by the same problem.

[foomench]

1. You really have to stir a lot at the beginning of the mash to get rid of pockets with different temperatures. Before good stirring and a little time to stabilize, I see significant temp variation. Even after some stabilize time if I haven't stirred well I can still see several degrees of variation. Stir stir stir.
2. I suspect that 6" probe going through all that hardware in the outlet of the mash tun is being affected by the ambient temperature, in particular if you aren't constantly pumping through that valve. There is some significant metal thermal mass there outside the cooler.
Just my opinions.

[NTabb]

I'm going to do another batch here Saturday (Orval Clone) and I'll definitely stir some more and see how the temps look. I constantly recalculate through the entire mash so I would expect it to level out over time, but I'm no professional by any means.

[Thirsty Boy]

Its my opinion that any mash temperature taken at any time except immediately after a thorough stirring of the mash... is a rough approximation at best.

I run a circulating system, and uniformity of mash temperature through the tun is one of the reasons I bother with it.

[Datamike]

I have a recirculating system that utilizes the same controller.

How are you heating the mash tun (if you are)?

Does this 9 degree difference subsist during the entire mash time?

I take my mash temp from the output as well, and after a few minutes of recirculation, the mash and the output are the same temp. I am using direct fire though, which given the plastic coolers, I am guessing you're not.

Michael

[NTabb]

I'm not heating the mash tun directly, but I have a heat exchanger with a heating element in the bottom cooler. The temp difference ranged from 6 to 9 degrees the entire time.

[Thirsty Boy]

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