Whole chicken

Maize gives the yellow. Maize holds xanthophylls, mostly lutein and zeaxanthin. The bird cannot make them. It absorbs them and stores them in the fat under the skin and in the outer skin. They are fat-soluble, so they sit where the fat renders and the skin browns. A maize-fed skin looks golden before any browning starts.

Age gives collagen crosslinks. A young bird has mostly immature collagen crosslinks. These break easily with heat, so a 6-week bird roasts tender. An older bird has more mature, heat-stable crosslinks. It needs long, wet heat. It also gives a stock that sets firmer, because it holds more collagen to convert to gelatin.

Exercise gives flavour. Outdoor range and a longer life move the leg muscle toward slow-twitch, oxidative fibres. These hold more myoglobin and more phospholipid. Phospholipids break down during cooking into aldehydes and other aroma compounds. That is the chicken smell. More phospholipid gives a more savoury leg.

Slow growth protects the breast. A fast-growing broiler often shows woody breast and white striping. The muscle grows faster than its blood supply. Fibrous tissue and fat replace some muscle fibre. The breast turns tough and stringy and holds water badly. A slow-growing breed mostly avoids this.

How to cook each. Take a young slow-growing bird to 60 to 65 °C in the breast for a roast. Hold an older bird at 85 to 90 °C in the thigh, covered, until the collagen converts.