Does Batch Size Affect Strike Temps?

[philm63]

Let’s run two experiments.

Assumptions are; 10-gallon stainless MLT, RO water, grain is a basic US 2-row crushed with a 2-roller mill at 180 rpm and 0.040”. Strike water is in the MLT and is holding at 160°F. Crushed grain is 70°F. Room ambient is 70°F. Grain is added at the same rate for both experiments and stirred the same way for the same amount of time to achieve a uniform mash.

Exp. 1) If we add 1 pound of grain to 1.5 quarts of water, for purposes of this experiment let’s assume the resulting mash temperature will settle at 150°F.

Exp. 2) If we add 10 pounds of grain to 15 quarts of water, would the resulting mash temperature also be 150°F?

 

[day_trippr]

I'm going to say "No", and propose Exp. 2 temperature should be higher then Exp. 1, because of equipment thermal losses...

Cheers!

 

[philm63]

Interesting. What might be some considerations when quantifying these thermal losses? Crush? Grain type? I know these are minimal in the big picture, but certainly I'd like to understand these variables.

 

[catalanotte]

From my own system, I went from 5 to 10 gallon batches in the same mash tun (15 gal igloo) and observed my strike water temps (same 1.25 qt/lb) were producing 3-4 degree higher mash temps. I was within a degree previously. I can only assume the energy loss to the mash tun isn’t appreciably greater when full as opposed to half full.

 

[day_trippr]

The crux of the comparison is found in the shared thermal loss.

Allow me to conjure up a model out of thin air.

- one quart of your mash contains 1000 BTUs of thermal energy at the start
- the mash tun bottom and fixtures require 100 BTUs to reach mash temperature
- the mash tun sidewall requires 10 BTUs per vertical inch to reach mash temperature

The 1.5 quart mash needs to heat the bottom plus an inch of sidewall = -110 BTUs leaving 1390 BTUs, or 926 BTUs per quart.
The 15 quart mash needs to heat the bottom plus 10 inches of sidewall = -200 BTUs leaving 14800 BTUs, or 986 BTUs per quart.

Cheers!

 

[philm63]

From your experience (speaking to all who read this), is there a simple rule that gets one close enough to hitting their strike temp with different size grain bills?

An example might look like this:
8 Lbs grain bill - Strike temp = mash temp + 10 F
12 Lbs grain bill - Strike temp = mash temp + 9 F
14 Lbs grain bill - Strike temp = mash temp + 8 F

I realize it's not linear due to the variables, just looking for rough guidelines. Looking to dial in my new system - brewed on it a couple times already and beers are coming out fine, but it's the process variables I'm trying to pin down. Currently I'm using a "recommended for my system" strike = 10 F above desired mash temp. Nailed the first strike, missed the second by 2 F low. Interesting to note; brew 1 was an 11 Lbs grain bill, brew 2 was a 9.5 lbs grain bill. Consistent with the comments above.

 

[Bobby_M]

Its generally easier to do this with software. The models used for combining x amount of grain at A temp with y amount of grain at B temp is pretty standard and predictable. The equipment losses are a little harder so its easier to go into the tun about 10F hotter and stir until the temp drops to the grain accomdation temp. In my days of using a cooler mash tun for example, I would go in at 175F, cool to 163F and then dough in to 1.25 qts per lb. That made for a very stable 154F.

 

[hottpeper13]

I do both 5 and 10 gal batches and I preheat my tun for 10 min or so and as long as I use the same ratio I end up with the same strike temps. Are you sure your grain temps were the same? My grain temps change with the seasons so that is my variable. Look at the formula in Palmers How to Brew and you'll see. when brewing with a buddy of mine I have to add in a degree or two because he takes forever to stir the mash. I use a huge whisk and am done in 30 sec to 1 min.

 

[kevin58]

Using Beersmith with a proper equipment profile built up, the software calculates strike temperatures factoring in your mash tun thermal properties, grain bill size, grain temp, water to grain ratio etc.

 

[bracconiere]

i'm not a scientist, but i've heard that water can hold a lot of thermal energy....more so then probably malt....so it'd probably be some sorta logarithmic thingy...

here's some plagiarism for you:

If you are using Fahrenheit, Pounds and Quarts then you’ll need to change the constant of 0.41 to 0.2

Strike Water Temperature Tw = (0.41 / R)(T2 – T1) + T2

• Wa = The amount of infusion water to add
• Wm = The total amount of water in the mash
• T1 = The initial mash temperature (temperature of dry grain for initial infusion)
• T2 = The target mash temperature
• Tw = the actual temperature of the infusion water
• G = The amount of grain in the mash
• R = The ratio of grain to water in the mash

 

[mongoose33]

I do both 5 and 10 gal batches and I preheat my tun for 10 min or so and as long as I use the same ratio I end up with the same strike temps. Are you sure your grain temps were the same? My grain temps change with the seasons so that is my variable. Look at the formula in Palmers How to Brew and you'll see. when brewing with a buddy of mine I have to add in a degree or two because he takes forever to stir the mash. I use a huge whisk and am done in 30 sec to 1 min.

This is an observation that illustrates @day_trippr's example above. If you preheat the tun, there aren't going to be any appreciable heat losses to heating up the tun with the water/grain mixture.

And as far as @bracconiere's comment about water being able to hold greater thermal energy than grain....one name for that kind of thing is thermal mass. Yes, water has a much greater thermal mass than an equivalent volume of grain.

It's why in some passive solar heating applications people will use water barrels (or decorative containers) as heat storage warmed by the sun which then gives up its heat at night after the sun sets. Other significant thermal masses are things like masonry, concrete, tile, and so on. The nice thing about using water is you can tune the amount of thermal mass simply by adding or removing water as needed.