How does the presence of dissolved oxygen in distillery water affect the Maillard reaction during mashing?

Dissolved oxygen in distillery water hinders the Maillard reaction during mashing. The Maillard reaction is a non-enzymatic browning reaction between reducing sugars (like glucose and fructose) and amino acids, typically occurring at higher temperatures. It's responsible for developing desirable flavors and colors in many food and beverage processes. In mashing, however, we don't want uncontrolled Maillard reactions. Dissolved oxygen promotes oxidation reactions that compete with the Maillard reaction. Specifically, oxygen can oxidize reducing sugars and amino acids, the very reactants needed for the Maillard reaction to occur. These oxidized compounds are no longer available to participate in the Maillard reaction. Example: Oxygen reacting with amino acids to create aldehydes or other byproducts instead. Secondly, dissolved oxygen can lead to the formation of undesirable off-flavors. Oxidation of lipids and other compounds in the mash can create stale or cardboard-like flavors. These flavors can be carried through fermentation and distillation, negatively impacting the final spirit. Therefore, distillers often de-aerate their water before mashing, either through boiling or mechanical deaeration, to minimize oxidation and allow for controlled enzymatic activity and flavor development without unwanted Maillard-derived or oxidation-derived off-flavors.