So I'm brewing a hefe on Thursday and am going to try my hand at doing a decoction mash. I'm taking the mash schedule from Brewing With Wheat, which is mash in 105 raise to 112 for 25 minutes pull a 40% decoction, heat it to 160 for 15 minutes, boil for 20 minutes adding that back in to the mash will bring to 147 for 20 minutes raise to 160 for 30 minutes raise to 170 for mash out The one thing I wasn't clear on was how do I know I'm pulling about 40%? Am I just estimating when I've pulled a little bit less than half the volume from the mash? Thanks for your help!
Unless you want to try to calculate it by weight, I wouldn't bother. Most of your enzymes are going to stay in the water (in the mash tun) after you pull your grain. I'd treat it like you're just trying to heat portage or oatmeal. 155ish for 10 min, and then get up to a boil for about 10 more. Your decoction is just going to get you up to your next temp level and add a little color and caramelization. You can even leave some of the grist in the pot that you are decocting in. It's better to have too much than not enough in your pot. Adding grains leftover from decoction 1, to decoction 2 is ok. You don't want to be low on your temp or you'll need to get your temp up with more hot water or with an additional decoction. You won't destroy too much diastatic power in this process and you'll do fine!
If you do calculate using software be aware that the software might low ball the amount. It seemed to do so for us (making hitting temps a little harder) and I believe others have said as much. If you just do it by hand, I believe it is something like 1-1.25 qt. per pound of grist. Here is a nice vid to watch Here is some more info (the dotted lines on the charts represent the decoction temps/time while the main line is the overall mash temp)
What type of mash tun do you have? I like doing decoctions, but for a time my big issue was the temp of the main mash during the decoction. I mashed in my (uninsulated) brew kettle, and the low volume of the main mash after removing 30-40% just couldn't hold temp. It was hard to hit that higher target after adding the decoction back. Switching to an igloo cooler mash tun fixed that. Be sure the mash you pull for the decoction is "thick" (mostly grist with some, but not much, liquid). The diastatic enzymes are mostly in the liquid soon after mash-in, so boiling a thick decoction preserves most of the enzymes (since they're not boiled in the decoction). You have to stir nearly constantly to prevent scorching. Good luck!
Keep extra hot and cold water around for quick temp adjustments. Stir the decotion often when boilin to avoid burning or sticking.
YES!!! I neglected stirring one time during a decoction, and it was a huge pain in the ass to get the scorched grains off the bottom of my kettle. There are still black scorch marks on the thing... OP, enjoy your first decoction! It's fun and smells amazing. Good luck!
