Short answer
The Maillard reaction is a cascade between reducing sugars and amino groups from proteins or amino acids that produces brown polymers called melanoidins and hundreds of flavour compounds. It is the brown on toast, a seared steak, roasted coffee and a pretzel crust. It speeds up with heat, dryness and higher pH and slows sharply in acid and in wet food held near boiling point, which is why browning happens on surfaces that have dried out.
The reaction starts when the carbonyl group of a reducing sugar — glucose, fructose, lactose, maltose; not table sugar until it has split — reacts with a free amino group on an amino acid or protein. The early products are colourless. They rearrange, fragment and recombine into reactive intermediates, which then polymerise into large brown, nitrogen-containing molecules called melanoidins. Along the way the reaction throws off the volatile compounds behind roasted, toasted and meaty flavours. Colour is the late, visible end of a long chain of chemistry.
Water holds the temperature of food near 100°C and dilutes the reactants, so a boiled potato never browns. Once a surface dries, its temperature can climb well above boiling and the reaction accelerates. That is why patting meat dry, not crowding the pan and a hot oven all give better colour. pH matters too: the reaction runs faster in mildly alkaline conditions, which is why pretzels dipped in alkaline solution brown so deeply, and it is strongly suppressed in acid. Maillard chemistry is not limited to cooking: it proceeds slowly in storage, even refrigerated or frozen, which is one reason milk powder and dried foods darken with age.
A little bicarbonate on onions or on a chicken skin browns them faster; too much gives a soapy taste.
Food scientists usually follow Maillard browning by the absorbance of a solution at around 420 nm, in the violet-blue where brown products absorb strongly, or by measuring the CIELAB lightness and yellowness of a surface with a colorimeter. The two do not always agree: absorbance tracks the amount of brown material in solution, while surface colour depends on texture, gloss and fat. Coffee roasters and bakers use surface colour; researchers comparing reaction conditions use absorbance.
Three different chemistries all make food brown, and they are often confused. Maillard browning needs amino groups. Caramelisation is sugar alone breaking down at higher temperatures. Enzymatic browning is an oxygen-driven reaction of phenolic compounds catalysed by enzymes, and needs no heat at all — it is the brown on a cut apple. Most cooked foods involve at least two: a crème brûlée top is mostly caramelisation, while the crust on bread is mostly Maillard.
Why: Too much surface water or an overcrowded pan keeps the surface near 100°C.
Fix: Dry the surface, heat the pan fully and cook in batches.
Why: Low surface sugar and high moisture; acidic marinades also slow browning.
Fix: Parboil and rough up the surface, dry well, and use enough hot fat.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactStrong evidence
The Maillard reaction is a non-enzymatic browning reaction between reducing sugars and amino compounds that produces melanoidins and flavour compounds; its rate depends on temperature, pH and water activity.
FactModerate evidence
A pH of 5 or below is generally sufficient to stop the Maillard reaction under moderate heating (up to about 100°C for less than 24 hours).
Caveat: A generalisation from the review; at higher temperatures browning can still occur in acidic foods.
FactModerate evidence
Maillard reactions continue slowly during cold storage, including refrigerated and frozen storage, as shown by increasing browning markers over months.
FactModerate evidence
Maillard browning in model systems is commonly quantified by absorbance at 420 nm.
Source: A model system based on glucose–arginine to monitor the properties of Maillard reaction products; Maillard Reaction: Mechanism, Influencing Parameters, Advantages, Disadvantages, and Food Industrial Applications: A Review
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.