Maillard Reactions: How Low Can They Go?

Reader Choi asks:

Joe, I understand that the browning of pumpernickel in the oven is caused by the Maillard reaction. It is my understanding that Maillard reactions only happen over 300 degrees Fahrenheit. If you’re baking pumpernickel at 225, how is Maillard browning possible?

That’s a puzzler isn’t it, Choi? Maillard reactions are so little understood. What is known is that they can happen at surprisingly low temperatures. They happen fastest over 300 degrees, there’s no question about that, but they can happen at far lower temperatures over time. Balsamic vinegar is a classic example of Maillard reactions that occur over a period of not minutes or hours but years, at temperatures at or below 70 degrees Fahrenheit.

A lot of factors influence Maillard reactions including amino acids, sugars, moisture content, temperature and pH. I wish I knew how. Usually alkalinity helps Maillard browning, it certainly does where pretzels and bagels are concerned. Pumpernickel dough is by contrast acidic, so who the heck knows what’s really going on in there? As I mentioned earlier, one thing that defines rye is that it’s a soup of microbes, half-digested starches, sugars, proteins and who knows what else. God help the microbiologist tasked with sorting all that out. Someday someone will…maybe. Thanks, Choi!

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