Variance in mash temp... what have I missed?

[brian_muz]

Hi BeerSmith brains trust. Looking for some advice on a problem I had with my latest brew.

I really wanted to nail my mash temp this time around. I was after a mash temp of 66.5 degrees C and BeerSmith recommended a mash in temp of X (Don?t have BS handy at the moment). I thought the best way to nail this was to NOT adjust for mash tun temp. Instead I added water a few degrees higher than the recommended strike water temp and left the mash tun alone for 15-20 mins until my thermopen showed It had cooled to the exact strike temp recommended. My thinking was that with this time the mash tun would have settled into temp nicely. I?d also measured and updated the grain temp and everything seemed perfect.

I wasn?t expecting the mash temp to be right to the tenth of a degree but when I check then temp five mins into the mash it was 2.2 degrees C too high (I took the temp at multiple points in the mash. There was about 0.3 degrees variance each way at points but 2.2 was the average).

2.2 degrees seem like a significant variance. Is there some variable I?m not accounting for?

I ended up dipping a piece of stainless steel I?d placed in the freezer into the mash briefly and it dropped to the right temp quickly. I just really want to dial in this strike water/mash temp scenario so I don?t need to do this in the future.

[Oginme]

By not adjusting for mash temp, I am assuming that you have the box to account for equipment temperature unchecked.  While this works well for some systems, it does not take into account the thermal mass of the mash tun when making its calculations for strike temperature.  So when you preheat the mash tun to above your strike temperature, you now have both the water and the mash tun at your strike temperature and using that combined mass and temperature to bring the grist load up to mash temp. 

What I do for my BIAB system is to check the box, Set the mash tun temperature on the mash tab to the desired mash temperature, now adjust the temperature of the mash tun to the strike temperature (this may take a couple of iterations, as adjusting the temperature will affect your strike temp.  Once you have done this a couple of times, it will pretty much become easy to see the offset you need to set the equipment temperature from strike temperature to bring you close enough.  I generally hit my mash temperature within a few tenths of a degree F (about a tenth of a degree C).

When I use my mash tun, I just let the program calculate the entire temperature rise for both the grain and mash tun and it works very well.  It took a couple of brews to get the specific heat of the mash tun set correctly, since it is a combination of metal fittings and false bottom combined with a plastic Gott-style cooler.  Here also, once dialed in correctly, it brings me to within a tenth or two F of my target mash temp.

[brian_muz]

Thanks heaps. Great reply. I don?t know how I missed that the mash tun was at strike temp, not mash temp, so this was going to increase the mash temp above what BS calculates.

I?m not quite following your BIAB process. So you check the box to adjust for equipment temp, then you set your mash tun temp to match strike, which then changes your strike temp, so you go back and forth with this until they both match. Is that a good summary?

I used to try just ticking the box to adjust for mash temp and then setting the mash tun and grain temp variables. It worked reasonably well but could still be off by a couple of degrees C. Plus I found it took a while for the whole thing to balance out when I mashed in. I thought pre heating the mash tun would allow me to mash in at the precise temp and have all the equipment already at temp from the second I mashed in. Plus it removes the variable of heat loss due to transfer between the HLT and mash tun. I?m pretty sure this is where my variance was coming from.

Anyway. Thanks again. Great advice.

[Oginme]

I?m not quite following your BIAB process. So you check the box to adjust for equipment temp, then you set your mash tun temp to match strike, which then changes your strike temp, so you go back and forth with this until they both match. Is that a good summary?

Yes, that pretty much captures it.  After a couple of times, you kind of get the feel for the offset and just add a degree or two to the mash temp and enter that in the mash tun temperature field.

[dtapke]

I thought pre heating the mash tun would allow me to mash in at the precise temp and have all the equipment already at temp from the second I mashed in. Plus it removes the variable of heat loss due to transfer between the HLT and mash tun. I?m pretty sure this is where my variance was coming from.

If you pre-heated your grain, mash tun, any piping/pumps, etc, than yes, you would remove most of the heat loss variables.

I allow the system to adjust my strike temp for me, this took about 4 or 5 batches to dial in perfectly by adjusting the thermal capacity of the system by altering the "mash tun specific heat" in my equipment profile.

strike water a little too low? raise the mash tun specific heat.
strike water a little too high? lower it.

adjust based on real measurements. if you were shooting for 66.5 and you got 64 with a strike temp of 68, then up the specific heat until the mash requests a strike temp of 70.5, then try that on a batch and see what happens.