Iam with pedro there, i have done a tripple decoction and after reading NBLB part on dection over and over again i saw now reason to actually decoct to mash out.
For mash out its a simply matter of just infusing up to the temp.
generally the decoctions will be before the sac rest. In a tripple decoction i had two sac rest one at 60c for 30mins and one at 70c for 30 mins.
All up i mashed in at 40c decocted up to 50 then to 60 then to 70c and just infused up to 78c, for mash out, As far as i know this is the most common techniquie for a tripple decoction mash.
So if your only doing one decoction i would mash in at 50c then decoct up to 65-70c for the results your are after in a real decoction.
Like ray said early it does change colour dramatically and when you return the decocted part you see it is much darker than the main mash, Even so iam not sure how much clolour this actually adds to the finished beer as i have read some stuff that says there is not much colour increase in the final beer but i have also read some stuff that says there is a colour increase, so hey iam not too sure here.
The reason i did it was simply for the fun of doing it at least once and to say yeap i have done a decoction and pulled of a great beer with it, i still can't really say how much of a improvement over a standard mash it was but it was fun and didn't take that much longer.
In mine the 40c and 50c rest i didn't have any probs, the final beer had a perfect dense head with great retention.
Anyway if your giving it a crack software is the easiest way to work out how much volume you need to take out each time, i took just enough wort to cover the grains and added pure water if it did get to thick during the boil, i stood there stirring it the whole time which you'll have to do.
Have fun decoctors.
Cheers Jayse :chug: