Decoction volume for different water to grist ratio's.

[prankster1590]

I was planning on doing a double decoction as experiment. The information about getting the right volumes is a littlebit flimsy. I chose for the following equation.

Vd = volume of decoction
Vm = Total volume of mash
Tt = target temp
T0 = start temp
Tb = temp boiling
a = temp lost during transfer of boiling water to mashtun and warming up the mashtun

But the advice is to use a 1,25 qts/ib water to grist in a decoction. This equation might work for this water to grist ratio but if you would use a ratio of 2,5 qts/ib it would be a different mix with more water which needs a lot of energy to be warmer up. So you would underestimate the volume of boiling decoction to add back to the mashtun. In that case i would have to add coldwater to the mashtun to cool it down. But this means less spargewater. I could adept the a factor in the equation but this would need some trials to estimate the a factor.

So does this make sense? Is there an equation that als includes the water to grist ratio?

 

[DBhomebrew]

Isn't the water to grist ratio made moot by using the Total Volume of Mash? That includes both Volume of Strike Water and Mass of Grain.

Aren't there calculators for this?

 

[DBhomebrew]

I like this approach...

There are several formulas out there for calculating the decoction volume. Some of them are simple and others try to account for factors such as the heat capacity of the grains and the mash-tun. The easiest way however is to estimate the decoction volume with a simple formula like this:

decoction volume = total mash volume * (target temp - start temp) / (boil temp - start temp)

and add about 15 - 20%. The idea is to decoct more mash than necessary. When the decoction is added back to the main mash, it is not all added at once. Instead it is added in steps while the temperature of the mash is constantly checked. This requires a thorough mixing of the mash after each addition. Once the target temperature is reached the remaining decoction is left to cool and added once its temperature is close to the mash temperature. By doing so one can account for additional factors that effect the actually needed decoction volume such as: evaporation during the boil, unexpected temperature drop in the main mash and others.

https://braukaiser.com/wiki/index.php/Decoction_Mashing

 

[prankster1590]

Yes. you can also cool down the decoction with a bit of cold water. This means or less sparge water or a longer boil of the run off. You might be adding water anyways since part of the water has evaporated during the boiling of the decoction.

But a higher water content means that there is not enough boiling decoction to get from 35C (95F) to 65C (149F). Since water has a high heating capacity. The 1/3 rule of thump might apply for a mash of 1,25 qts/ib but i dont think it would for a 2,5 qrts/ib mash.

 

[DBhomebrew]

A) It seems to me that braukaiser's methodology organically adjusts the decoction volume to realized needs without requiring adjustment to sparge volume or boil time. Adding water to make up to account for decoction boil-off is a different thing.

B) Maybe 35° to 65° is too big a jump for a single decoction?

C) I have to assume that if braukaiser hasn't found a formula to accurately predict decoction volumes then it's a mighty high ask.

Note well my use of "seems to me", "maybe", and "assume".

 

[prankster1590]

A) It seems to me that braukaiser's methodology organically adjusts the decoction volume to realized needs without requiring adjustment to sparge volume or boil time. Adding water to make up to account for decoction boil-off is a different thing.

B) Maybe 35° to 65° is too big a jump for a single decoction?

C) I have to assume that if braukaiser hasn't found a formula to accurately predict decoction volumes then it's a mighty high ask.

Note well my use of "seems to me", "maybe", and "assume".

A) Not if you used all boiling mash and got to a temp below the target temp.

B) This might be the solution. Building the temp in steps by immediately boiling a part of the mash to increase the temp further.

C) Yes. A simplified formula for homebrewers with restrictions. I'll bet you that a pro brewery has very complex equations for these things. Its thermodynamica. Einsteins favorite science about the transfer of energies.

 

[RM-MN]

Since BIAB allows for a finer crush, often the mash efficiency will be higher that a conventional mash. If the mash effiiciency is high enough then a sparge isn't very critical. You can do a full volume mash with a conventional setup but since you depend on the grain hulls to make the filter bed you have limitations on the milling and that leads to lower mash efficiency. To make up for that inefficiency, you do sparges to capture as much of the sugars as reasonable.

 

[DBhomebrew]

with BIAB you're essentially mashing with the total pre-boil volume

Typically, perhaps. BIAB is not defined by full volume mash. I employ a 50% of pre-boil volume sparge with every batch. I've also employed step mashing and there's nothing to keep me from decoction.

 

[hottpeper13]

When I do a decoction mash I strike with a 1:1 ratio for 97*-104*,then add boiling liquor to hit 143* then pull decoctions from there. This way it only stays at the low temp for 20 min. The ratio gose to between 1.5 - 2 :1. Way easer to pull grain then at 1.25:1.