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Impact of the water under mash screen

sciyan

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Hi

I've been searching all over the forum and almost find my answer to my question.

I have a 15,5 gallons keg as a mash tun. I have a mash screen that cover to bottom and I need at least 2 galons of water to reach it. I also use a pump that leave almost nothing as a "dead space". I've read in several topic that if I want beer smith to calculate the right amount of water for the water/grain ratio I need to put a negative value in the "lauter tun dead space" that equal the value of the water needed to reach the mash screen.

Others tell that I just need to recalculate manualy what is the real water/grain ratio considering the water volume that I need to add into the mash to make sure it cover the mash screen.

I've tried both and I don't have consistent temperature for my mashing in temp. Is anyone know which way is the right way to configure BS ?

Thanks

Here a couple of topics that talks about that situation :

http://www.beersmith.com/forum/index.php/topic,1177.0/prev_next,prev.html#new
http://www.beersmith.com/forum/index.php/topic,1831.msg7348.html#msg7348
http://www.beersmith.com/forum/index.php/topic,3972.msg17589.html#msg17589
http://www.beersmith.com/forum/index.php/topic,6617.msg26424.html#msg26424
http://www.beersmith.com/forum/index.php/topic,3509.msg15661.html#msg15661
http://www.beersmith.com/forum/index.php/topic,4138.msg18186.html#msg18186
http://www.beersmith.com/forum/index.php/topic,6404.msg25614.html#msg25614
http://www.beersmith.com/forum/index.php/topic,3591.msg15993.html#msg15993
 
Scyian-

The next to last thread is directly on point.  Brad has acknowleged this as a current limitation of BS. 

What the negative deadspace does is subtract the volume from the required sparge volume.  Then, you have to compensate by adding that water directly to the mash-tun.  But, you have to do that without telling beersmith.  If you add the water to the mash-step then beersmith will further adjust the sparge water downwards.  However, if you don't tell beersmith that there is 2 gallons of water in the mash-tun then the thermal calculation will be wrong. 

There is a way out though.  Change your mash-tun properties in the equipment profile to include the 2 gallons of water.  2 gallons weighs 16 lbs, and had a specific heat of 1.0 cal/gram-degC.  You need to calculate the weighted average specific heat for the MLT with water in it:

(MLT_specific_heat*MLT_weight + Water_weight*1.0) / (MLT_weight + Water_weight)

To be proper, the above should be mass_in_grams (instead of weight_in_pounds), but it doesn't matter because we are dividing  lbs by lbs...so the units cancel out.

On brew-day, you need to be sure to put 2 gallons of water into the MLT, let the temperature of the water and MLT equalize, and accurately measure the temperature of the MLT+2g_water.  Then put the measured MLT_water temp into BS.  Finally, be sure that the "adjust temp for Equipment" is checked.

Now your equipment profile defines a magic MLT that has a very high heat capacity and creates 2 gallons of water going into your boil kettle.  Because your MLT has so much mass and a much higher specific heat, it has a much larger heat capacity.  Therefore, it is much more important to ACCURATELY measure its temperature...errors will have a more profound effect.  You can minimize this impact by preheating the MLT+water to somewhere closer to your desired mash-temp.  Use the same thermometer for all measurements.

I think that should work, without carrying any errors into the boil kettle or fermentor.  In addition, your efficiency should still be calculable, and BS OG calculations should also still work.  Other than being a little "odd", I can't think of a downside to this approach.  It just isn't very intuitive.

Let me know.
 
Sciyan (sorry, spelled your name wrong above)-

Curious, did this help?

-tch
 
Sorry. Didn't had the time yet. But I printed your reply and will test it in weeks to come.

Thanks
 
Your info helped me, but I switch for the lazy option  :)

I just decrease a little bit the mash tun specific heat and add the missing volume with my strike water. I usualy reach the right temperature, but still a little to high, but I've done only 2 batch yet. At the end of fall I will have gather enough data to adjust the parameters and get good results for the initial strike water.

Bye
 
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