Maillard Reactions 101: Theory

Charlie Scandrett,

Posted to HBD 2390, 4/4/97

There are three basic non-enzymic browning reactions,
  1. Pyrolysis
  2. Caramelisation
  3. Maillard reactions.
PYROLYSIS is simply scorching,(from the greek "pyro" - burning) and involves the total loss of water from the sugar molecule and the breaking of carbon-carbon linkages, i.e. the *destruction* of the sugar molecule. This is what happened when your grandmother neglected the "candy" she was making for toffee apples. The result was a burnt and inedible flavour.
CARAMELISATION is a heat induced *transformation* of reducing sugars alone in a *concentrated* solution, through so called "anhydro sugars". In this reaction the simpler sugars *lose water molecules from their structure* through a process called "1:2 & 2:3-enolisation". This process is influenced by pH and is a "steering" process for both Caramel and Maillard reactions. Through many intermediates, and in the pH 2-7 range, D-fructose for example can give rise to the Furans, Isomaltol and Maltol, well known bread crust flavour/aromas. No compounds containing nitrogen result.

The commercial production of beer "caramel" is produced by boiling fermentable *sugars* in the presence of ammonia, so it is really partly a Maillard reaction ( a bitter one too). Ammonia is a source of nitrogen for this reaction, because the pure Caramel reaction alone doesn't produce enough *colour*. The solution is boiled until it thickens and the boiling point reaches 130°C. Further thickening or a rise in temperature is then avoided until the desired colour/flavour is reached. The pH is about 4-6 and it is called a "positive" caramel because that is the electric charge of the resulting molecules. "Negative" caramels are produced at higher temperatures and form different compounds and can affect clarity of drinks. MAILLARD browning reactions involve simple sugars and amino acids and simple peptides. They proceed during the kilning of malt, and during wort boiling. They begin to occur at lower temperatures and at higher dilutions than caramelisation. The rate can increase by 2-3 times for each 10°C rise in temperature. However even long term storage of malt extract will Maillard-brown at room temperature. Prize winning dark beers have been coloured by this method as they had none of the harshness of some high temperature Maillard reactions in roasted malts.

Maillard reactions have three basic phases.

The outcome will depend on which amino acids and sugars are available, and what the pH and temperature aand concentration are. Charlie (Brisbane, Australia)