[flbrewer]

The last batch I made I was able to hit my mast temp. within a degree. The one caveat is that I didn't stir the grain very long, which I plan to do this go around. My fear is that I'll undershoot my temp.

Do you have a good rule of thumb on what temp. to heat the strike water up to to hit a particular mash temp?

FWIW, I'm using a 10 gallon rubbermaid round MT and my mash temp. target will be 153.

[fmader]

Each system is different. It also depends on how you transfer the water. On average, my strike temp is 16 degrees over my target mash. If my mash is thinner, I'll drop the strike a couple degrees. If it's thicker, I might raise it. I think it's just something that you get a feel for.

[flbrewer]

Just to confirm...it's easier to just let it cool naturally vs. trying to heat up correct? Maybe I'll err on the hotter side just to be safe until I know.

[S. cerevisiae]

It would help to know your strike liquor to grist ratio (i.e., quarts per pound).

[flbrewer]

It would help to know your strike liquor to grist ratio (i.e., quarts per pound).

I think I'm using 1.5. Actually, at this point I Just try and get equal volumes of water for my strike and sparge water to simplify my process at this point which normally is around 1.5 based on my inputs.

[jtoots]

Just to confirm...it's easier to just let it cool naturally vs. trying to heat up correct? Maybe I'll err on the hotter side just to be safe until I know.

Yep.  Stir until you drop it to your goal.  I've overshot by quite a bit a couple times, and I just added a bit of cool water, then subtracted this quantity from my sparge volume.  A little bit goes a long way.

[reverseapachemaster]

I would rather come in a couple degrees under with a uniform mash temperature than take a measurement that appears right but came out of a mash with pockets or layers of different temperatures.

[S. cerevisiae]

What is your grain temperature?

Here's the basic formula for calculating strike temperature.

strike_liquor_temperature = (.2 / hot_liquor_to_grist_ratio_in_quarts_per_pound) x (desired_strike_temperature - grist_temperature) + desired_strike_temperature
 
Example

grist_temperature = 25C/77F
strike_temperature = 66C/151F
hot_liquor_to_grist_ratio_in_quarts_per_pound = 1.5

strike_liquor_temperature = (0.2 / 1.5) * (151 - 77) + 151 =  0.13  *  74 + 151 =  161F (72C)

The trickiest part of calculating a strike liquor temperature value is determining the thermal loss to the tun itself.  You will need to add 4 to 6 degrees Fahrenheit to strike_liquor_temperature to account for this heat loss. I would add 6 because you are using a large tun for the amount of grist that you are using.  As an alternative, you can preheat your tun, and then just go with strike_liquor_temperature.   If you do not mind overshooting a bit, I would use strike liquor that is 16 degrees (18 degrees will definitely give you room to adjust down) hotter than your desired rest temperature.  As you have assumed, it is better to overshoot and cool than to undershoot and have to calculate the amount of hot liquor at 100C/212F necessary to hit your strike temperature.

strike_liquor_temperature_accounting_for_tun_loss (approximate) =   (.2 / hot_liquor_to_grist_ratio_in_quarts_per_pound) x (desired_strike_temperature - grist_temperature) + desired_strike_temperature + 6 (Fahrenheit)     

strike_liquor_temperature_accounting_for_tun_loss (approximate) =   (.2 / hot_liquor_to_grist_ratio_in_quarts_per_pound) x (desired_strike_temperature - grist_temperature) + desired_strike_temperature + 3.3 (Celcius)     

[denny]

Just to confirm...it's easier to just let it cool naturally vs. trying to heat up correct? Maybe I'll err on the hotter side just to be safe until I know.

Keep some ice cubes handy.  If you overshoot, stir a few into your mash.

[Steve Ruch]

Just to confirm...it's easier to just let it cool naturally vs. trying to heat up correct? Maybe I'll err on the hotter side just to be safe until I know.

Keep some ice cubes handy.  If you overshoot, stir a few into your mash.

Good idea. My SOP has been to add room temperature water which can take quite a while. Some times I give it up when I get kinda close. Luckily I know my system pretty well and usually get pretty close on the first shot.

[denny]

Good idea. My SOP has been to add room temperature water which can take quite a while. Some times I give it up when I get kinda close. Luckily I know my system pretty well and usually get pretty close on the first shot.

I always have a bowl of ice handy anyway for my "Cheap'n'Easy" hydrometer reading technique.

[S. cerevisiae]

Keep some ice cubes handy.  If you overshoot, stir a few into your mash.

+1

Denny is correct.  Ice is better than water when it comes to cooling a mash with a minimal increase in volume. It takes almost as much heat energy to thaw a gallon of water in ice form at 32F to liquid form at 32F as it takes heat a gallon of water from 32F to 212F.  This amount of heat energy is called the latent heat of fusion.  Latent heat of fusion is covered in the "Heat transfer and refrigeration" chapter of "Brewing" by Lewis and Young.

[flbrewer]

You guys are ok. 

[Frankenbrew]

You guys are ok.

+1

[jimmykx250]

Good idea. My SOP has been to add room temperature water which can take quite a while. Some times I give it up when I get kinda close. Luckily I know my system pretty well and usually get pretty close on the first shot.

I always have a bowl of ice handy anyway for my "Cheap'n'Easy" hydrometer reading technique.

Denny what is the cheap and easy
Hydrometer reading method?