Dough in the main mash at 95F. When RO water and standard lager malt are used, the mash pH should stabilize around 5.8, 5.7. Add sour malt to reduce pH to 5.5 - 5.3 range.
Rest the decoction at 122F for 15 minutes, then increase the temperature to 155F and rest the decoction for 20 minutes. An iodine test can be performed after the sacc rest. The color of the iodine should be reddish brown. If the iodine turns black, not to worry. Raise the temperature to boiling and boil the decoction for at least 20 minutes.
Skim off any hot break that forms when the decoction is boiling.
The mash will darken, do not confuse the initial darkening of the mash as maillard or the formation of mellanoidin. For mellanoildin to form by using a single decoction all of the ducks have to line up. Generally, boil times of 45 minutes and longer are needed to form 1st decoction maillard reaction and mellanoidin.
Use the decoction to reach a higher end proteinase temp or a beta temp in the main mash. Refer to the malt data sheet for beta alpha ratio. If beta is on the low side, extend the maltose/B-limit dextrinization rest period and reduce main mash pH to 5.2 - 5 range. Lowering the pH will stagger alpha and allow beta to catch up, converting glucose into maltose. Conversion doesn't really have anything to do with starch. Rather, conversion takes place when beta chops off a couple of molecules of glucose from the non-reducing end formed at the time when alpha liquefied a 1-4 link of the amylose starch chain, mixes the glucose with water and maltose is born. When there is a good maltose to glucose ratio in the wort, fermentation smooths out and a secondary fermenter might be needed.
Boiling the decoction will release amylopectin. When amylopectin forms, enzymes switch gears. Amylopectin is responsible for body. The infusion method skips the step.
Something to consider; when mash is doughed in at 130F or so, the brewmaster is now on enzymes time clock. The 1st decoction has to be worked with quickly, because Saccharification will occur at 130F in time. For that reason it is better to dough in at temperature's at which enzymes are working in slow motion. By using lower doughing in temps the brewmaster can work on the 1st decoction without being stressed out. The 1st decoction sets everything in motion. Brew on!!!