pyrazines

In 1912 the French physician and chemist Louis-Camille Maillard sent a two-page note to the Académie des sciences describing what happens when amino acids are heated with sugars, a paper about protein chemistry and the dark melanoidins he was trying to understand, not about cooking. It took four decades for food science to fully claim him: the scheme still taught today was set out by John Hodge in 1953. Pyrazines are the ring compounds that cascade ends in, and this library plates them constantly: the browned base of beef and onion in abo shalhoob, roasted cocoa baked into the egg-free brownies, toasted almonds and pine nuts crowning a mansaf, and, in the Japanese curry, a base built three separate times over, once each in the onion, the seared beef and the toasting flour.

Pyrazines are not one substance but a family of nitrogen-containing rings, dozens of them, each with its own smell and its own potency. They form at the tail end of the Maillard cascade, after a sugar and an amino acid have condensed, rearranged and broken into small reactive dicarbonyls that then attack a second amino acid and cyclise. Potency swings wildly between them: a study of thirteen alkylpyrazines found odour detection thresholds spanning 4 to 490 parts per billion, and two isomers differing only in the position of one methyl group, 2-ethyl-3,5-dimethylpyrazine and 2-ethyl-3,6-dimethylpyrazine, sit at 0.04 and 8.6 micrograms per litre: moving that one methyl group around the ring changes detectability by more than two hundredfold. The 140 to 165 degree figure everyone quotes for browning only marks when it turns fast and visible, not a switch it crosses.

What pyrazines carry is smell rather than taste: roasted, toasted, nutty notes, potent enough at a few parts per billion that a crust reads before it is tasted. Push the same cascade too far in a starchy food and it produces acrylamide instead, traced to the amino acid asparagine reacting with sugar above about 120 degrees. Browning to gold rather than dark brown keeps the flavour without that cost. In this library the family is traced in seven recipes, sometimes built twice or three times over inside a single pot.