Strike Temp Calculations

[osgrimmy]

Hello,

I'm looking for a Strike Temp formula that takes into consideration grain weight. Currently I am using this below formula from John Palmer:

Strike Water Temperature Tw = (.2/r)(T2 - T1) + T2

r=1.25 quartz per lbs grain
T2= Desired mash temp
T3= Temp of grain

Example
(0.2/1.25)*(154-60)+154 = 169.04 F


I would like to see the difference in formulas from one that takes the weight into consideration and one that does not. Also I have noticed a difference in results from various online java calculators.


Thanks,
Grimmy

 

[Grizzlybrew]

I don't have a formula to contribute off the top of my head, but...

More than the weight of the grain, I would be interested in a formula that accounts for the thermal absorbtion of the mash tun.

 

[Hammy71]

http://www.brewheads.com/batch.php accounts for thermal loss of mash tun...

 

[Scooby_Brew]

I found that it's difficult to find the thermal loss of a mash tun, and it's just another unnecessary variable complicating things. I just pour in the strike water first, stir and wait a few minutes so the water temp. drops to my desirable strike temp and then mash in. So my mash tun thermal loss is 0.

 

[albannach]

The variable "r" is basically a ratio of water_volume/grain_weight
therefore the grain weight is actually "in" that equation already
(and the "T3 & T1" variable [typo in original equation] adjust how much influence that grain weight will have on the final temperature "Tw")

by the way, big fan of your website grimmy, see my sig

 

[ajf]

Specific heat of water is 1.0 cal / gram / degree C
Specific heat of malt is 0.4 cal / gram / degree C


Assume you have 5 Kg grain at 20 C that you need to mash at 66C with 6 L water.

You need to raise the temp of the grain by 46 C, so you will need 5 * 0.4 * 46 Kcal = 92 Kcal
Divide the 92 Kcal by 6 L = 15.3 to get the extra temperature of the strike water in C, so the required strike temp would be 66 + 15.3 = 81.3 C.

If you want to convert this into US measurements, you should find it closely approximates Palmer's formula. His formula does take weight into consideration by the definition of "r"

Trying to take the effect of the mash tun into consideration is much more difficult.
Multiplying the mass of the mash tun by it's specific heat (which a lot of brewing software does) can be very inaccurate, as that assumes that the tun is evenly warmed from top to bottom. It isn't. Those areas of the tun that are in contact with the grain are warmed to the mash temperature. Those areas above the grain bed, are hardly warmed at all.

-a.

 

[Orfy]

Way to much math.

Follow some one who uses the pretty much the same set up and dial it in from there.

Unless you like the math.

 

[wilserbrewer]

http://www.rackers.org/calcs.shtml

 

[bolts]

I worked this out a while back from various references, one i recall is linked below. I used to have the mash tun worked into this also, but found it to be too unpredictable. I just pre-heat the mash tun.

I've also noticed that I need to fudge the number by adding +2. It seems to be the amount of time it takes to get the strike water from the kettle to the mash tun and stirred in. I'm consistently within .5 degree with this.

Ts = ( Tm * Wv + (Gm * 0.05)) - Tg * Gm * 0.05 ) / Wv

Ts = strike water temp
Tm = mash target temp
Wv = strike water volume
Gm = grain mass
Tg = grain temp

0.05 = specific heat of barley for english units F, lb, gallons

Use 0.41868 for metric units (kg, C, liters)

(see article for more explanation)

A recent batch I did with a 156 target, 7.76 gallons of water and 23lb of grain @ 68 degrees.

( 156 * (7.76 + 23 * 0.05 ) - 68 * 23 * 0.05 ) / 7.76
(1389.96 - 78.2) / 7.76 = 169.04

Palmer's is the same
(.2 / r) ( T2 - T1 ) + T2
(.2 / 1.35 ) ( 156 - 68 ) + 156
= 169.04

http://brewingtechniques.com/library/backissues/issue4.5/miller.html