Help me wrap my brain around decoctions

Hi,

I would like to brew the "Pious Traditional" (http://www.homebrewtalk.com/showthread.php?t=147815) and need some help in understanding the decoction steps.

My setup is a 10-gal electric BIAB with recirculating PID temperature control.

Here are the decoction steps from the recipe:
(I am going to scale this down to a 3-gal batch, but let's go with the published values for this post.)

Mash Schedule: Decoction Mash, Double
Total Grain Weight: 16.00 lb
----------------------------
Decoction Mash, Double
Step Time Name Description Step Temp
10 min Protein Rest Add 32.00 qt of water at 137.5 F 132.0 F
30 min Saccharification Decoct 8.79 qt of mash and boil it 151.0 F
30 min Saccharification Decoct 4.85 qt of mash and boil it 159.0 F


So, the first part I think I get: add the grains to 32 quarts @ 137.5 F, which brings the temp down to 132.0 F. I would initially set my PID to 137.5 F, and then lower it to 132.0 F for the 10-min protein rest.

I then remove 8.79 qt of mash (grains using a sieve? water plus grains?) and bring to a boil. But this is where I am confused. Bringing it to a boil takes time. When does the 30 minutes start? What temp should I set my PID to while the boiling is happening?

Any clarifications would be welcome! Thanks.

 

Your goal for the first decoction is to enable a sacc rest in the main kettle at 151F for 30 minutes. Keep the main mash PID on 132F. Remove the 8.79 qt of grains (avoid the liquid), bring to a boil in a separate pot, then return them to the main kettle. Their heat brings the 132F mash to 151F, where you then hold it for 30 minutes with PID set to 151F.

You need to stir the decocted grains constantly to avoid scorching as they heat to a boil.

Follow the same protocol for the second decoction.

I found this BTV episode very helpful:
http://brewingtv.com/episodes/2011/3/29/brewing-tv-episode-34-decoction-day.html

 

You could simply turn the PID off for the 10 minutes plus the time it takes to bring the grist to a boil as a decoction. The extra time for the grist to come to a boil is of no real consequence. Once your decocted grist is brought to a boil, you return it to the mash to (hopefully) bring the whole mash to 151. At this point you turn the PID to 151 (in case your decoction didn't raise the temp enough) and hold it there for the 30 minutes. The 30 minutes starts when the mash gets to 151. The second decoction is optional in my opinion. You have the means to quickly raise the temperature with your PID and recirculation which wasn't available 100 years ago so they had to use decoction or direct heat and it was easier to hit the temp with decocting.

You could just not do this as a decociton since you have the means to raise the temp pretty precisely with your system but you would miss the flavor that the decoction is supposed to impart. The second decoction probably won't make such a big difference in the flavor.

 

Thanks for the replies, McKnuckle and RM-MN! I think I have it figured out now. That BTV episode was helpful in visualizing the process.

Many thanks, and Cheers!