In the process of malting, developments are made to ensure enzyme content is available for starch conversion, and cell walls become porous. During the latter part of processing, moisture is removed and synthesized enzymes are left in a state of “dormancy”. Upon rehydration, these enzymes will continue where they left off, primarily catalyzing starch degrading reactions. Because of this, the start of the brewing process begins with hot water, and, as with every step of brewing, temperature is very important. Get a good thermometer like this one from Hanna Instruments.
A host of enzymes are present in the mashing process. Depending on a brewer's preference, a single-infusion mash, constant ramp, or series of steps can manipulate malted barley into a cacophony of reactions. Each enzyme will respond differently to temperature, so procedure has a large effect. Single infusion temperature rests offer the best chance at consistency, however their impact on final product is limited. With one temperature, enzymatic activity will be a balance across the spectrum with some seeing little to no influence at all on the wort composition.
Constant temperature ramping is a traditional mashing method employed for a long time. This is certainly effective at creating highly fermentable wort compositions and increasing overall extraction, however there are some potential concerns. Increased activity by certain proteases can break down foam-positive proteins or leave the resultant wort “watery” or thin. Stepping the mash procedure through several temperatures is an ideal way to maximize extraction and tailor wort composition. Short rests at lower temperatures allow proteolytic enzymes to breakdown needed amino nitrogen and peptides for healthy fermentation, without the loss of body. Quickly increasing the temperature moves these enzymes to a less active state, whilst increasing amylase activity for saccharification. Later on, temperature can be increased again, denaturing enzymes and virtually stopping all mash activity.