Mash Temperature Calculations

While I have been homebrewing for 40 years, I am new to BeerSmith.  I have been using my own spreadsheet which, after calibration, has given me very accurate strike water temperatures.  BeerSmith called for strike temperatures up to 10 degrees lower, so I adjusted the specific heat constant (I use a very simple 7 gallon plastic pail for a tun) to get temperatures to match my spreadsheet.  All well and good.  However I noted that the strike temperature of BeerSmith does not vary regardless of how much grain is being mashed based on a fixed dilution rate.  It is most notable for small partial mashes where the specific heat of the tun is a bigger factor. And yes, I have checked the box to adjust temperature for equipment.  As an engineer I have faith in my thermodynamic calcs in my spreadsheet and the empirical evidence that they are accurate.  I know the relationship is not linear and therefore the strike water temperatures should vary somewhat given a constant dilution rate.  Am I doing something wrong or is this an inherent limitation in BeerSmith?  Other than this one issue, I've found the software to be intuitive and excellent, a great product.

Interesting observation.  I ran the following test.  I formulated a recipe with 20 lbs of grain at 60F with a mash temp of 153F.  My mash tum (a converted keg weighs 30.95 pounds and Beer Smith is set to use a specific heat of .12, which is BeerSmith's default for stainless. My mash tun was also set to 60F.  At 1.25 qts per pound BeerSmith says to add 25 qts at 171.2F.  If I change the amount of grain to 10 lbs,  BeerSmith says to add 12.5 qts at 171.2F, just as you reported and an obvious error.  However, if I use the  Strike/Infusion tool  with 12.5 qts for 10 lbs at 60F I get an infusion water temperature of 179.8F and with 25 qts for 20 lbs I get an infusion water temperature of 173.2F.  An obvious problem here.  The tool does not have a way to independently set the mash tun temperature so I do not know just what temperature was used for the mash tun.

I ran a second test.  Again with 20 lbs of grain but this time with a mash temp of 154F. Using the Adjust Mash Temp tool I input 30.95 lbs for my mash tun (the tool did not ask what it was made of and this may be part of the problem) I set the target temperature to 168F and the temperature of the adjusting water to 212F.  The tool stated that I need 7.34 qts of boiling water.  In the recipe I attempted to adjust the mash out temp to 168F by adding 7.35 qts and it indicated that the adjusting water temperature would have to be 222.6F.  By adjusting the amount of water until I got close to a temperature of 212F the recipe indicates that it would take 9.65 qts if my equipment is included and 9.19 qts if not.  This is closer to my experience but still a little short in that I generally have to add 11 to 12 qts of boiling water to hit 168F.  I am sure that part of this is that the tool fails to consider the dead space volume in my Mash/Lauter Tun and this wort also has to be heated when I am recirculating to help clear my wort, which I always do.  Looks like the temperature calculations need to be looked at and corrected.

Hi,
  I believe part of the difference is that BeerSmith accounts for differences in mash volume.  For example, if you have a 15 gallon sankey keg for a mash tun but you are using only 5 gallons of it for the mash then you do not necessarily heat the entire mash tun to 150F.  BeerSmith attempts to compensate by only including a portion of the equipment effect proportional to the volume used.  That is why your 20lb and 10lb examples have similar strike temperatures.

  The mash tool does not have separate settings for mash tun specific heat and some starting temperatures, which is why the recipe calculator is slightly more accurate.  It assumes a temperature near room temperature, and moderate specific heat.  In cases like the second one which you illustrate this can have a significant effect - especially for a large mash tun that is cold.

Cheers,
Brad

I also have a converted 15.5 gal keg for a mash tun, I also am an engineer and I also created my own formula for strike water temp. I always hit it right on the money and my calculations consider grain amount and temperature and strike water amount but I always pre-heat my mash tun with boiling water. This eliminates most, if not all, of the heat absorbed by the tun. My tun is well insulated with Styrofoam (like 4 inches thick) so my mash temp. remains constant for the entire 90 minuets. Hope this helps.

haf

This is probably the most challenging thing to set up.  I still need to fuss around and lock in my profile. My new but sob sob idle brewery is 15gal sanke boiler and hlt with a 15gal icecube cooler tun. I batch sparge so anyone that has mastered something similiar-feel free to share your knowledge.

I use a 10 gallon round Igloo cooler for my tun and I have found that my mash temps are closer to where I planned when I don't figure for the tun. If anything, I find that my initial strike temp is usually a couple of degrees high.