Author Topic: are your temps always off?  (Read 7004 times)

Offline itsratso

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are your temps always off?
« on: September 12, 2013, 07:53:48 PM »
new all grain brewer here. i was amazed how far off my BS specifc heat estimates were according to the attached spreadsheet. BS estimates my igloo cooler 10 gal tun at .30, i got .17 almost half that amount! i haven't brewed yet with the new numbers but i would imagine this would have to change some things. you might want to check your numbers with it too. (if you don't have MS office it runs fine on the free openoffice). weigh your mash tun, put in however many gallons you want (1-2 gallons is easier/faster to heat, i checked it with 1 gallon and 3 gallons and got the same numbers). it will automatically calulate the weight for the gallons you put in. have your tun at room temp is easiest, put that in for tun temp. you don't need to boil your water, i used mash temps (160F).

Offline grathan

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Re: are your temps always off?
« Reply #1 on: September 13, 2013, 05:37:57 AM »
You're gonna end up changing it back. Just sayin'.

Offline MaltLicker

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Re: are your temps always off?
« Reply #2 on: September 13, 2013, 08:58:37 AM »
Agreed.  I can see different coolers that have different types of plastics, different wall thickness and thus insulating ability having slightly different specific heat numbers, but in the range of +/- one or two points.   And I'd think it would be far easier to work on accuracy of water volumes and temperatures, and eventually learn that your system is 1-2F hotter or colder than BS2 estimates, and just adjust your water temps to accommodate. 

Specific Heat is the amount of energy required to move it 1C, I think.   It's hard to fathom that you have a igloo cooler that behaves more than s/s than plastic. 

s/s                   your igloo cooler                                            most igloo coolers
0.12                 0.17                                                               0.30


Offline itsratso

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Re: are your temps always off?
« Reply #3 on: September 13, 2013, 03:02:15 PM »
seemed way off to me too. i checked it 3 times so i know the process was accurate. but i can also see a kind of sense in it? i would imagine with the valve and false bottom that the SS parts weigh about as much as the cooler does?

Offline MaltLicker

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Re: are your temps always off?
« Reply #4 on: September 13, 2013, 05:37:00 PM »
I'm not an engineer, but I would think it has much more to do with total surface area?   And even with metal fittings and valves, a cooler MLT is probably 98% plastic surface area. 

I'm not doubting the spreadsheet so much, but do think there's usually more sensitive factors that have much sway on hitting the mash-in temps. 

Let us know how it works out.

Offline philm63

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Re: are your temps always off?
« Reply #5 on: September 13, 2013, 06:19:07 PM »
I tend to agree with grathan on this one as well - leave it set to plastic, and make minor adjustments in your process each time you brew and as I said before; take copious notes so you know what to adjust next time.

Because it is very difficult to calculate exactly how much heat-energy a given plastic cooler will steal away from your mash water (so many variables), I eliminate this variable by preheating my cooler before I use it - just add a bunch of hot tap water (mash-temp works fine) and let it sit while preparing the grains - dump that water, add grains and new (filtered) water and mash away.

Some even put their mash water in the tun a few degrees over the calculated strike temp and watch it until it hits the right temp and then they dump the grains in - I'm probably going to try this next time to save a step - preheat the tun with the mash water, then dough-in - it seems it may be more consistent this way.
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Offline Scott Ickes

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Re: are your temps always off?
« Reply #6 on: September 13, 2013, 07:30:27 PM »

Some even put their mash water in the tun a few degrees over the calculated strike temp and watch it until it hits the right temp and then they dump the grains in - I'm probably going to try this next time to save a step - preheat the tun with the mash water, then dough-in - it seems it may be more consistent this way.

This is what I do.  I hit my mash temperature within 1F each and every time.  It basically takes the cooler out of the equation.  I just heat my strike water to 8F above my strike temperature and pour it in.  Within about 5 minutes it's down to strike temperature and has preheated my cooler MLT at the same time.
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Offline itsratso

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Re: are your temps always off?
« Reply #7 on: September 13, 2013, 07:57:29 PM »
yeah, that is what i did last time. i just thought it was kind of interesting how much this differed from BS. i am going to try it both ways and see what works better. i noticed on one of my recipes that i changed to this that the mash temp only changed two degrees (which may actually be the two degrees that most people are off by it seems?). something fun to play with anyways.

Offline brewingmike

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Re: are your temps always off?
« Reply #8 on: December 11, 2013, 03:46:50 AM »
I had a similar problem with temps.  I calclated strike water at 1.5 qts/lb for 3 sessions and hit my temps dead on.  I then changed the calc in BS2.

Offline philm63

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Re: are your temps always off?
« Reply #9 on: December 11, 2013, 06:30:02 AM »
Funny thing - as I had mentioned during my last post in this thread; I was going to preheat my plastic tun with the actual strike water and dump the grains in once the calculated strike temp had been reached - didn't work. Twice!

Two separate brew days I used this "preheat with strike water and dump grains in" method and both times I missed my mash-in temp high by right around 8 F.

Before; when I preheated the tun and dumped the preheat water, and put the grain in the empty tun and poured the strike water through a hose from the HLT onto the grain while stirring (took about 3 or 4 minutes), I was nailing my mash temps dead on.

Seems I failed to consider a couple of critical variables - specific heat of the tun, and of the grain; they respond differently based on the two different mash-in methods. Apparently, dumping the grains into the strike water, (faster process), doesn't dissipate as much heat as the other way around (slower process), and I hadn't considered that difference in rate of change.

Soooo... seeing as I am taking the specific heat equation out of the formula by preheating the tun, and then pouring the grain into the strike water, I thought I'd screw around with the calculator a bit and see what happens.

Seems if I set the Tun Specific Heat to -0.2 (used to be 0.3), I get a corresponding drop in calculated strike temp equal to about 8 F - same amount by which I was missing my mash-in on the high side, so this should give me a calculated strike temp in my mash profile that better corresponds to my system and method as it exists today.

I'm going to try this on my next brew and I'll report back.
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Offline kcbeersnob

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Re: are your temps always off?
« Reply #10 on: December 12, 2013, 06:34:10 AM »
Interesting.  If my target temp doesn't land spot-on, it's within 1°F.  I use a 10g Rubbermaid beverage cooler with a stainless braid.  I am using the default specific heat setting.  I typically use a water to grist ratio between 1.5:1 and 1.9:1.  My process:
  • Measure the grain temp within 5 min of mashing in and adjust my target temp accordingly
  • Heat my strike water to 3-4°F hotter than my target temp
  • Transfer the strike water to the cooler through the ball valve on my kettle
  • Put the lid on and wait for the temp to fall to my target (usually takes <5 min)
  • Pour the grain in very carefully, stirring constantly to prevent dough balls
  • After all of the grain is in, stir for another ~30 sec
  • Screw on the lid and set the timer

I find that the cooler maintains temp within 1°F for an hour rest--quite independent of weather conditions.  I used to use preheat water and dump before infusing, but changed to the process above due to greater process efficiency. 

Offline philm63

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Re: are your temps always off?
« Reply #11 on: December 12, 2013, 07:08:54 AM »
...I typically use a water to grist ratio between 1.5:1 and 1.9:1.

Yeah, I think I may have been going too tight on my mash lately - been using a 1.2:1 water to grain ratio and I don't think I'm getting enough consistency throughout the tun with such a tight mash.

My next batch will use a 1.5:1 ratio but I still plan on going with a modified specific heat setting in my equipment profile for my 10-G plastic cooler so the number that shows up in my mash profile will be a more accurate strike temp. Still got lots to learn here, it appears.
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Offline Bajaedition

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Re: are your temps always off?
« Reply #12 on: December 15, 2013, 09:33:52 AM »
I brewed for years with a friend and he had a heated area our brew system was. It took us about 3 tries and we knew how to hit strike temp every time. After about 10 years I moved and sold out my share of the brewery to him. When I got to the new place I built a system and used it for about 8 years, I had that in my garage so after that I had to figure in ambient temp to my strike figures. Well I sold that system and moved. Now I have been here a year and am slowly putting together another all grain system. Technology has moved on and I am designing a mash tun that I can do step mash without applying flame to the tun.
I know I will have to experiment once again to get where I can hit strike temps but OH WELL that is just part of the "Lore O Brewing".
Funny thing about it all, is that for the last year I have been doing extract beers again. I have gotten a whole new appreciation for it as it has proven to me that you have a ton more control over an extract brew than you think.
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