Ok, so we've made the jump to all-grain brewing, and almost all of our batches have come out short of the intended volume of 5.5 gal. I realized going in that water management was going to be a bigger deal than when we were doing extract brewing, but I honestly thought I could ballpark it. That turned out to be an incorrect assumption.
Last time, Mark plugged everything into Beersmith and we did considerably better than we'd done before, but we still came out short. Beersmith has all the math, but it couldn't correct for the fact that we didn't have any numbers for how our actually equipment functioned in real life. Today, I set out to change that.
I decided to work backward to make the math a little easier on my beer-addled brain. I started with the brew kettle. We're brewing in a keg-turned-kettle that holds 15 gallons of liquid. We'll generally will need to boil something over 5.5 gallons, so we can account for loss from evaporation. To figure out how much, though, I needed to boil 5 gallons of water for 60 minutes to see how much we actually lose from this setup.
5 gallons of water and an hour later, I had my answer. Given a rolling boil over our outdoor gas burner for 60 minutes, Mark and I lose (!!) 1.75 gallons of water. Well, no WONDER we've been short! That's almost a 25% loss to evaporation. To end up with 5.5 gallons of beer in the carboy we need to start the boil with no less than 7.25 gallons of wort.
(Note: I suspect my numbers may be a little of, because the rule of thumb loss to evaporation is 10%! More testing needed.)
Next, I took the mash tun and poured water into it until it began to drain from the mash tun's spigot. It's not a perfect calculation, because in the real world, we'll be adding grain to the tun and it will effect the amount of wort that ends up left in the tun. This would be a good ballpark to start, and for each batch after today, I can measure what ends up left in the mash tun, and begin to take an average for future batches. It turns out that without grain, .75 gallons of liquid end up left in the mash tun after draining (without manual intervention - we can tip the mash tun and lower that to about .5 gallons).
Ok, so this gives us some constants to start with. So, here comes the math:
(Note: This is a slightly adjusted version of the Calculating Mash Water Volume guide from Brew365)
Assumptions
Loss to grain absorption = 0.2 gal / lb grain
Loss to mash tun = 0.75 gal
Loss to evaporation = 35 % / hr
Shrinkage = 4%
Mash Thickness Ratio = 0.3125 gal/lb
*Shrinkage is the loss of volume due to cooling from boiling to 60 degrees. It's a minor factor, but we'll consider it, because BEER.
Desired Result
12 lb grain (for this next batch - will vary)
5.5 gal final volume (can also vary, but it's what we go for most right now)
60 min boil (again, can vary, but the next batch will be 60)
Mash process Loss Calculation
Taking the assumption that we lose .2 gallons of water per pound of grain, and that leftover wort in my mash tun totals .75 gallons, we can calculate the expected loss of water to the mash process with 12 lb of grains.
Mash Loss = mash tun loss + (grain absorption * lbs of grain)
Mash Loss = .75 + ( 0.2 * 12 )
Mash Loss = .75 + 2.4 = 3.15 gallons
Evaporation Loss Calculation
To find the percentage evaporation loss, the formula is as follows:
Evaporation Pct = 100 - ( post boil volume * 100 / pre-boil volume)
Evaporation Pct = 100 - ( 3.75 * 100 / 5 )
Evaporation Pct = 100 - 75 = 25
25% loss to evaporation based on my equipment's performance. As stated earlier, that's a good bit above the 10% generally accepted evaporation.
Full Kettle Loss Calculation
So, now that we know the evaporation loss, we can calculate the total loss of liquid in the kettle.
First we need to get the Evaporation Loss and Shrinkage Loss factors.
Evaporation Loss Factor
ELF = 1 - (Evaporation % * ( boil duration / 60 ))
ELF = 1 - (.25 * ( 60 / 60 ))
ELF = 1 - (.25 * 1)
ELF = 1 - .25 = .75
Shrinkage Loss Factor
SLF = 1 - Shrinkage %
SLF = 1 - 0.4
SLF = .96
Now on to the total Kettle Loss:
Kettle Loss = ((Batch Volume + Loss to Trub*) / ShrinkageFactor) / EvaporationFactor)
(Note: Loss to Trub isn't something I'm worried about, but you can subtract it if you like)
Kettle Loss = (( 5.5 + 0 ) / .96 ) / .75 )
Kettle Loss = 5.73 / .75 = 7.6 gallons
Total Water Needed Calculation
Ok, so knowing the above, we can calculate the final total amount of water needed for our batch.
Total Water Needed = Kettle Loss + Mash Process Loss
Total Water Needed = 7.6 + 3.15 = 10.75 gallons
Alright, so now we have the total water needed, we can see how much we need for mash water and how much we can use for sparging. Here, we use the generally accepted mash thickness ration of 0.3125 gallons water / lb of grain.
Mash Water = (Mash Thickness Ratio * Pounds of Grain )
Mash Water = ( 0.3125 * 12 )
Mash Water = 3.75 gallons
So, FINALLY, our last calculation:
Sparge Water = Total Water Needed - Mash Water
Sparge Water = 10.75 - 3.75 = 7 gallons
So there you have it. Using the formulas and method from Brew365's Calculating Mash Water Volume guide, and assuming our equipment's 25% evaporation loss, a 60 minute boil and 12 pounds of grain, Mark and I will need 10.75 gallons of hot water, 3.75 to be used in the mash and 7 for our sparging.
Looks like it'll be a long heating time in the hot liquor tun for our next batch, the White House Honey Porter!
No comments:
Post a Comment