Mash Tun Heat Capacity - confusion

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Mash Tun Heat Capacity - confusion

Postby slothrob » Tue Mar 27, 2007 11:39 am

I've used the tun calibration somewhat successfully for hitting the neighborhood of my mash temperature, but have blamed any low mash temperatures on my low brewing environment temperature.

Now, I'm making a batch with a very small grain bill and a very specific mash temperature I want to hit. For these reasons, I intend to mash by adding grain to water that has preheated my tun and stabilized at my strike temperature.

So, I want to circumvent my heat capacity calculations. I did this by ceating a new vessel, giving it all the same dimensions as my other tun, but leaving the heat capacity at "0".

Here's the problem:
The tun with a positive heat capacity gives me a lower strike water temperature than the tun with no heat capacity (for the same grain, volume, and mash temp settings).

Am I confused, or is this backwards?
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Re: Mash Tun Heat Capacity - confusion

Postby jeff » Tue Mar 27, 2007 1:01 pm

slothrob wrote:The tun with a positive heat capacity gives me a lower strike water temperature than the tun with no heat capacity (for the same grain, volume, and mash temp settings).

Am I confused, or is this backwards?


The strike water temperature is lower because the system that includes heat capacity from the vessel has a greater capacity to store heat than the system that has water alone. Without the added heat absorbed by the vessel factored in, the heat capacity of the water by itself is what is used to raise the temperature of the grist.
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Postby slothrob » Tue Mar 27, 2007 1:12 pm

I thought the formula would have been designed to work in the opposite direction. i.e., when adding water to a tun with heat capacity, some heat will be absorbed by the tun. If the tun has no heat capacity, then the water would lose no heat to the tun.

So your formula is actually designed to work in a system where the water is already in the tun and stabilized (at the predicted strike temperature), to which the grain is then added, NOT a system where water (at the strike temperature) is added to a room temperature tun holding room temperature grain, correct?
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Postby jeff » Tue Mar 27, 2007 1:20 pm

slothrob wrote:So your formula is actually designed to work in a system where the water is already in the tun and stabilized (at the predicted strike temperature), to which the grain is then added, NOT a system where water (at the strike temperature) is added to a room temperature tun holding room temperature grain, correct?


That depends on whether you have selected a heating vessel or not. If you select a heating vessel then BTP assumes that the water is heated and then added to the mash vessel. If no heating vessel is selected, then BTP assumes that the water is heated in the mash vessel. Does there seem to be an error in the calculations?
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Postby bzwrxbz » Tue Mar 27, 2007 1:50 pm

jeff wrote:... If no heating vessel is selected, then BTP assumes that the water is heated in the mash vessel...


OMG... all my numbers in BTP have been pretty perfect except for strike temps... I have had to offset a little bit to hit them, and I could never figure out why. I had always figured it was because of my crappy mash tun.

This explains it. I do not have a kettle selected, yet, i do fill a cooler type mash tun. I reconfigured some of my older schedules... and voila, this is where the discrepency is.

I see this documented in the wiki... but it is not mentioned as a "must do" type of thing...

well, on my next brew, we will see if i can hit my numbers without overdriving the strike temp.
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Postby slothrob » Tue Mar 27, 2007 2:19 pm

jeff wrote:That depends on whether you have selected a heating vessel or not. If you select a heating vessel then BTP assumes that the water is heated and then added to the mash vessel. If no heating vessel is selected, then BTP assumes that the water is heated in the mash vessel. Does there seem to be an error in the calculations?

I'll have to double check and let you know, but I'm pretty sure I made the same mistake as bxwrxbz. I assumed that since I wasn't heating the MASH, I didn't need a heating vessel, while I should have done the opposite. At the very least, I haven't been paying attention to wether I had a heating vessel specified, or not.

bzwrxbz wrote:OMG... all my numbers in BTP have been pretty perfect except for strike temps... I have had to offset a little bit to hit them, and I could never figure out why. I had always figured it was because of my crappy mash tun.
Well, on my next brew, we will see if i can hit my numbers without overdriving the strike temp.

I've been using the same kind of fudge factor, thinking my low room temperature was throwing off the calculations.
I'll get to check it when I skive work tomorrow for a session. Only thing is, I'm doing a step mash tomorrow, which I don't normally do, so it won't be a perfect test of my previous calculations.
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Postby jawbox » Tue Mar 27, 2007 6:51 pm

let's make that three people. I will check too.
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Postby jawbox » Tue Mar 27, 2007 6:57 pm

omg, now i know why i was always low on my mash in. It also explains why there was a difference between the values i got from beersmith and btp.

can someone do a basic tutorial to help new/other users?

later,
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Wiki Addition on "Mash In"

Postby bzwrxbz » Tue Mar 27, 2007 7:27 pm

I have modified the "Mash In" portion of the wiki to reflect what Jeff has said above. I pasted a couple of sentences from his above post, and added one myself.

here-> http://www.beertoolspro.com/wiki/Mash_In

anyone can feel free to add or modify it...

cheers!
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Checkbox Suggestion

Postby bzwrxbz » Tue Mar 27, 2007 7:36 pm

I suggest a checkbox be added to the "Mash In" popup that toggles the following->

x Direct Fired Mashtun

When it is checked, the "Heating Vessel" dropdown becomes disabled, or disappears, so it becomes obvious what is going on.

When it is not checked, the "Heating Vessel" dropdown becomes active, so the user can select the appropriate equipment...

just my 2 cents

cheers!
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Postby jawbox » Tue Mar 27, 2007 7:52 pm

also is there anyway of making the sparge steps a little more intuitive. I hate having to zero my residual. I would sooner have something to select that would automatically calc that i'm going to drain the whole tun.
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Postby slothrob » Wed Mar 28, 2007 4:34 am

I added a heating vessel to my Mash in and now the numbers make logical sense.

I'll test if the calculations work for me today.
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Postby slothrob » Wed Mar 28, 2007 10:56 am

Using the Mash In window correctly today and I was 1
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