Vol. VIII · Browning Plate 8 of 9burnt, bitter, acrylamide, toast, chips, fries, asparagine, golden, charring, go for goldMS

Burnt and Bitter.

The difference between golden toast and dark toast is flavour, bitterness and about three times the acrylamide.

Browning has no natural stopping point. Past deep brown the melanoidins and caramel polymers keep reacting, losing water and carbon dioxide; the surface turns black, the flavours turn acrid and bitter, and finally there is only carbon. A little char is a flavour in itself — grilled peppers, the edges of a pizza, 锅巴 at the bottom of the pot — but a burnt crust masks everything else.

Starchy foods have a second reason for restraint. In 2002 Swedish researchers found acrylamide, a probable human carcinogen in animal studies, in fried and baked potatoes, bread and coffee. It forms in the Maillard reaction itself, mainly from the amino acid asparagine with reducing sugars above about 120 °C, so it rises with colour. Food-safety agencies advise aiming for golden, not dark brown. The workshop browns a slice of toast or a chip at the surface temperature you choose.

Below: colour and acrylamide against minutes at the surface temperature you choose, with and without soaking cut potatoes (teaching rates; acrylamide relative to golden at 170 °C).

What you will learn
Workshop
Teaching model: colour is the course Maillard rate at one-tenth strength for a starchy surface; acrylamide forms at a course rate (activation energy 140 kJ/mol, a teaching value) and accumulates without levelling off, shown relative to a surface taken to golden at 170 °C. Soaking or blanching cut potatoes is shown as removing 40 % of the surface sugar.

Go for gold

In this model a surface at 175 °C turns golden in 3.2 min and dark brown in 11 min; by then it holds 3.3 times as much acrylamide as it did at golden, because the colour levels off while acrylamide keeps accumulating. Hotter is worse for the same colour: golden at 190 °C carries 1.19 times the acrylamide of golden at 170 °C. That is why guidance for chips is to fry at no more than 175 °C and stop at golden yellow.

Lower it further at the start. Soak cut potatoes in water for half an hour, or blanch them, to wash out surface sugar (the workshop's check box); dry them well before frying (VIII.2). Choose potatoes stored cool and dark, not sprouting. Toast bread to light gold. None of this makes browning dangerous in the ordinary diet — it is about choosing the lighter end of good colour. And keep char where it belongs: a blistered pepper skin, the bitter edge of a crème brûlée or 锅巴 are choices; a blackened fond or burnt onions are mistakes that no sauce rescues.

At the stove

Toast three slices of bread to pale, golden and dark brown and taste them side by side. Note where the flavour peaks and where bitterness begins; the golden slice is usually the best balance.

The Swedish discovery in 2002 began with a tunnel-building accident: workers exposed to an acrylamide sealant were being studied, and the control group turned out to have acrylamide in their blood too — from their diet.

Terms

Acrylamide
A compound formed from asparagine and sugars in browning starchy foods, a probable carcinogen in animal studies.
Asparagine
An amino acid abundant in potatoes and cereals; the main source of acrylamide.
Charring
Burning a surface to carbon; bitter and acrid.
锅巴
The crisp, browned rice crust at the bottom of the pot.
Past deep brown, browning becomes burning. Acrylamide rises with colour: stop at golden, fry no hotter than needed, soak cut potatoes.

Sources

  1. D. S. Mottram, B. L. Wedzicha and A. T. Dodson, "Acrylamide is formed in the Maillard reaction", Nature 419, 448–449 (2002); EFSA CONTAM Panel, Scientific Opinion on acrylamide in food, EFSA Journal 13(6):4104 (2015); Commission Regulation (EU) 2017/2158 on mitigation measures and benchmark levels. The course's formation rate is a teaching value.
  2. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.