Mash tun weight

[Bjarne]

Hi folks. I trying to calculate the temperature of the mash water befor mixing, aiming for 65 deg. C. I am using the Infusion calculator in BeerSmith. The only thing I wounder about is the Mash tun weight. I have read this is the weight of my empty mash tun. I am using a big plastic beach cooler. The calculated deg.C of the water changes very much if I do small adjustments here. Why is that? What does the weigth of the tun have to do with the temperature? Type of plastic, or space I would understand, but not the weight. Anyone?

Can it be that a steel tun will steal heat according to weight? More steel, more heat loss? What shall I put in the when using plastic, with very little heat loss?

[Oginme]

The temperature rise is a function of the initial temperature of the water and equipment (in your case the mash tun), the heat capacity of both AND the mass of each of the items.  You need the weight (mass) of the mash tun to know how much material needs to be raised in temperature.

[Bjarne]

TY for answer. I was also thinking that, but will there not be a big difference between steel and plastic?

[Bjarne]

I can see there is a field to put in Mash Tun Specific Heat. I guess this is where to adjust for the tun material?
Anybode know what nobmber to use when using a plastic cooler box?

One more thing. What does Initial Mash Temperature mean?

[Oginme]

The short answer is yes it makes a big difference.  I would start with using the recommended 0.30 for the heat capacity of the plastic.  Once you get a few results which give you an actual value of temperatures (grain/mash tun/strike water temps) and your ending temperature, you can adjust this value to get the number closer to your actual results.

Initial temperature will the the temperature your equipment and grain will be at the start of the mash.  You can make standard room temperatures for initially building your profile, but when you brew, use the actual temperatures of the grains and mash tun to give you a better, more accurate target for your strike temperature.  Generally, if the mash tun has been in place for a period of time, the temperature will be the same as the ambient temperature of the room; outdoors, it may be a bit different as the temperature may fluctuate depending upon conditions.