Vol. XX · Vegetables, Fruit and Legumes Plate 10 of 12fruit, cooking fruit, poaching, compote, apple sauce, pears, pectin, sugar syrup, ripening, ethylene, climacteric, bananas, avocados, citrus, 糖水MF

Fruit in Cooking.

Apples simmered in water make apple sauce; the same apples simmered in a heavy syrup stay in neat slices. The sugar holds them together.

Fruit is mostly water held in cells cemented by pectin (V.4), with sugars and acids that make it taste. Cooking softens it as the pectin breaks down (XX.2), but fruit's acidity slows that breakdown, and sugar slows it further: a strong syrup draws a little water out of the fruit by osmosis (XX.1) and strengthens the cell walls, so pears, quinces and apples poached in syrup hold their shape, while the same fruit stewed in water collapses. For sauces and jams that is what you want; for compotes, tarts and 糖水 it is not. Firmer varieties (cooking pears, Granny Smith) and adding sugar early keep pieces whole; soft, mealy varieties and adding sugar at the end make purée.

Ripeness matters, and fruit divides into two kinds. Climacteric fruit — bananas, avocados, mangoes, tomatoes, pears, peaches, kiwis — keeps ripening after picking, driven by the gas ethylene: buy them firm and ripen them at room temperature, faster in a paper bag with a ripe banana or apple. Non-climacteric fruit — citrus, grapes, strawberries, cherries, pineapple — does not ripen further once picked; it only softens and spoils, so it must be bought ripe. The workshop poaches pear slices.

Below: the breakdown of pectin in pear slices poached at the temperature you choose, in water or in syrup (reaction bench, course kinetics for pectin with a teaching factor for sugar), against minutes, with the point where slices start to fall apart.

What you will learn
Workshop
Reaction bench: first-order pectin breakdown with the course rate, times 0.4 in a heavy syrup (a teaching factor for sugar's firming in the measured direction); slices taken to fall apart beyond 70 % broken down. Ripening behaviour from standard post-harvest classifications.

Sugar early to keep, sugar late to purée

In this model pear slices poached at 95 °C in water begin to fall apart after about 30 minutes, in a heavy syrup after about 74; at a gentle 85 °C in water, about 68. So poach fruit gently in syrup to keep it whole — a pear in red wine and sugar can simmer half an hour and still stand on the plate — and stew it fast in a little water, sweetening at the end, to make a sauce.

Other fruit chemistry the cook uses: cut apples, pears and bananas brown by enzyme within minutes; lemon juice or a syrup slows it (VIII.6). Fresh pineapple, kiwi, papaya and figs carry protein-digesting enzymes that stop gelatin setting and soften meat; cooking kills them (X.8). Fruit high in pectin and acid (citrus peel, quince, sour apples) sets jams easily (XIII.6). Store ripe climacteric fruit in the fridge to slow it, but keep bananas and tomatoes out of the cold, which damages their texture and flavour.

At the stove

Poach two pears cut the same way: one in water, one in a syrup of equal weights sugar and water. Take a slice from each every ten minutes and see which keeps its shape.

Ethylene was identified as the ripening gas in 1934; long before, Chinese growers ripened fruit in rooms where incense was burned, and Egyptian growers gashed figs — both of which release ethylene.

Terms

Climacteric fruit
Fruit that keeps ripening after picking, driven by ethylene.
Ethylene
The gas that triggers ripening.
Poaching in syrup
Gentle cooking in sugar syrup, which keeps fruit whole.
Compote
Fruit cooked in syrup, pieces kept whole.
Fruit softens as pectin breaks down; sugar slows it, so fruit in syrup keeps its shape and fruit in water collapses. Climacteric fruit ripens after picking; others must be bought ripe.

Sources

  1. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
  2. H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.