Specific Heat of grain

Hi, I am brewing my first AG this week-end. I want to estimate my strike temperature for my mash, and I want to calculate it by myself.

It is a simple thermodynamic problem, but there is 1 unkown and it is the Specific Heat of grain.

I looked on the internet and I haven't found anything.

I found this website : http://www.brew365.com/mash_sparge_water_calculator.php which look interesting, but the strike temperature doesn't change with the quantity of grains and therefore, cannot be right (according to thermodynamics)

Does someone have this values?

Thank you

I just use room temp value.

If you have a smart phone, I have found that Brewzor is easier to use and accurate. I used to use that link and recently went back to it and found it clumsy in comparison.

Read this below from: http://www.brewingtechniques.com/library/backissues/issue4.5/miller.html

I learned the following basic formula for figuring the temperature of a mixture from Dan Carey in a talk he gave at the 1988 AHA conference:
Aa + Bb = Cc
The capital letters A, B, and C stand for the specific heats of grain, water, and the mash, respectively, and the lower case letters stand for temperatures of the same variables. What the formula says is that the product of the temperature and specific heat of a mixture will be equal to the sum of the products of the specific heat and temperature of the two substances that make up the mixture - in this case, water and grist.

I use this formula to calculate the strike temperature of my water for making a mash. For example, suppose my recipe calls for 825 lb of malt, and I want to use 285 gal of water to make up the mash, which should have a temperature of 153°F (67°C). To avoid a lot of extra calculations, I assign a value - 1 - to the specific heat of 1 gal of water. I assign the correct relative value - 0.05 - to the specific heat of 1 lb of grain (0.05 is correct for barley malt; it may not be exactly right for flakes, but it's close enough). If I then measure the temperature of the grain as 70°F (21°C), for example, I can calculate the correct strike temperature for the water.

First, I calculate the specific heat of the grain (A): 825 X 0.05, or 41.25. The specific heat of the water (B) is 285. And the specific heat of the mash (C) will be the sum of those two, or 326.25. The temperature of the grain (a) is 70°F (21°C), the temperature of the mash (c) should be 153°F (67°C), and the temperature of the strike water (b) is the unknown.

To solve for b, we simply work out the calculations:

Aa = 41.25 X 70 = 2887.5
Cc = 326.25 X 153 = 49916.25
Bb = 285b
2887.5 + 285b = 49916.25
285b = 49916.25 - 2887.5 = 47028.75
b = 47028.75/285 = 165.013°F (~74°C)

Hope it helps

Good explaination sickbrew. Although I am pretty familiar with this kind of calculations.

What I need is the specific heat (Cp) of the barley's grains.

From what I understand :

You put 1 to water which could be set as 4.187KJ/Kg*K (The real specific heat of water)
You put .05 to Barley, then to find the real specific heat of Barley, we keep the same ratio (1/.05) then the specific heat of Barley should be .21KJ/KG*K

This seems a bit small. What it means is that for 1degres lost of 1 kg of water, you have 20 degres rise of 1 kg of barley

BendBrewer said:

I just use room temp value.

If you have a smart phone, I have found that Brewzor is easier to use and accurate. I used to use that link and recently went back to it and found it clumsy in comparison.

Click to expand...

+1... if you have an Android phone get Brewzor Pro.. I used it last weekend when helping a friend brew.. used room temp as the grain temp.. added in the amount of grain and desired mash temp it gave me the temp for the strike water. hit the temps perfect.

Upon some further reading: The specific heat capacity of water is 1 btu/lb°F, and for malted barley it is around 0.38 Btu/lb°F.

Source:

http://forum.northernbrewer.com/viewtopic.php?f=5&t=97953
third post, third paragraph

cheers

Thanks Sickbrew, I'll try that and I will adjust for future receipe, but It looks like a good value to start!

Don't forget to either account for the heat absorbption of your mash tun or pre-heat it.

Your formula is on the right track, but all the mechanical engineers out there are cringing at the mix of units.

First, to answer the original question, the specific heat capacity of malted grain is about 0.38 Btu/lb°F. Specific heat capacity of water is 1.0 Btu/lb°F.

Now back to the math...

The amount of heat energy in any substance (water, grain, mash) depends on the amount of that substance, the specific heat capacity of the substance, and the difference in temperature from some reference:

Q = m ∙ Cp ∙ dT

Where:
m is the mass in lb (or kg)
Cp is the specific heat capacity in Btu/lb°F (or kJ/kg∙K)
dT is the temperature difference in °F (or °C)

The other important relationship here is conservation of energy -- for the mashing process, the heat in the water (w) plus the heat in the grain (g) equals the heat in the mash (m).

Qw + Qg = Qm

Combining the above two equations:

(m∙Cp∙dT)w + (m∙Cp∙dT)g = (m∙Cp∙dT)m

I won't go into the details from here, but just want to point out that the units here are (lb) ∙ (Btu/lb°F) ∙ (°F). That means the water volume (gallons) has to be converted to mass (pounds). The density of water at room temperature is about 8.33 lb/gal, dropping to about 8 lb/gal at boiling temperature. After using the magic of engineering and mathematics, you can get a formula for the amount, or temperature, of strike water needed, based on known values for the mass and temperature of the grain, the desired mash temperature.

Now back to the original post, you used a value of 1 for the "specific heat" of 1 gal of water, and 0.05 for the "specific heat" of 1 lb of grain. If you instead use the correct units I mentioned above, 1 gal of water has a heat capacity of (1 gal)x(8 lb/gal)x(1.0 Btu/lb°F) = 8 Btu/gal°F, and 1 lb of grain has a heat capacity of 0.38 Btu/lb°F. The ratio of grain to water is 0.38/8 = 0.0475 ... approximately 0.05. So the approach you described is okay, but just need to be careful that you are talking about *gallons* of water (volume) and *pounds* of grain (mass).

For most brewers, you would probably rather just use any of the great calculators or software out there. For the engineering geeks, all you really needed to know was in the second paragraph of this post.

Moose1231 said:

but the strike temperature doesn't change with the quantity of grains and therefore, cannot be right (according to thermodynamics)

Click to expand...

I just wanted to touch on this statement. While I do agree its probably a bit simplified, wouldn't the fact that the amount of water is proportional to the amount of grain you add play a part? IE, if you add another pound of grain, you add another 1.25 quarts (or whatever ratio you standardize) of water. It's not like you'd ever add more grain and not also add more water (at least you shouldn't).

Wow, it seems like minded people consider things like this. I too was trying to get to the bottom of this a while ago before I just said the heck with it. I'm glad people are looking into this too. I also was interested in the specific heat of grain for the process of step mashing in a cooler MLT. I will tell you from experience that I simplified that one to being merely the specific heat of water. So I simplified to get the following formula to calculate a resulting mash temp. It's close enough for government work.
(V1T1+V2T2)/(V1+V2)=T3
I believe this will also help you if you need to do a mash correction... however I think it's awesome to see people working this out more exactly.

Cheers to any other scientists, engineers, mathematicians or moon-lighters!

Edit: we can figure out just how significant a role the amount of grain plays by evaluating the percentage mass of the entire mash it occupies. I'll come back to this thread later once I've considered this more

Okay, I just did a bunch of unit analysis based on a mash water/grain ratio of 1.5 quarts per lb grain. Of course this gets ugly because pounds mass and pounds force are easily confused. I converted to ft^3 for volume (more data can be found in this unit) and used room temperature density, since when we measure out our mash water it is usually around there, if not colder.

Anyways, I hope I did all of the calculations correctly, but it comes out to roughly 100.69 lbm H2O per lbm grain. So I suppose the grain is significant enough to have an effect, but perhaps not enough that neglecting it would be much of an issue. Assuming a specific heat identical to that of water probably wouldn't cause significant error. But I think it's great to shoot for precision.

Moose1231 said:

Hi, I am brewing my first AG this week-end. I want to estimate my strike temperature for my mash, and I want to calculate it by myself.

It is a simple thermodynamic problem, but there is 1 unkown and it is the Specific Heat of grain.

I looked on the internet and I haven't found anything.

I found this website : NameBright - Coming Soon which look interesting, but the strike temperature doesn't change with the quantity of grains and therefore, cannot be right (according to thermodynamics)

Does someone have this values?

Thank you

Click to expand...

I calculated 1.67 KJ/K.kg, apologies if this is already in above replies in different units.