Ch.7: A Survey of Common Fruits

Chapter 7 of the book "On Food and Cooking: The Science and Lore of the Kitchen" by Harold McGee (1984) The Making of Fruit: Ripening Common Fruits of Temperate Climates Fruits from Warm Climates

160 flashcards · Other · by lakesare

Part of Public › Books › On Food and Cooking (Harold McGee) · 16 courses

1. [A Survey of Common Fruits] Why are most fruits delicious raw, while most vegetables taste better cooked?

   Plants make fruits to be eaten, so they fill them with sugar, acid and aroma. Animals that eat fruits spread the seeds. Vegetables are other plant parts, with mild flavors (roots, leaves) or harsh defensive ones (onions, cabbage), and cooking improves them.

2. [A Survey of Common Fruits] What gives a fruit its basic taste, before its aroma?

   The balance of sweet (sugars) and sour (acids). As a rule, the sweeter a fruit, the better; but a sweet fruit with no acidity tastes flat.

3. [The Making of Fruit: Ripening] Young vegetables are at their most tender. Are unripe fruits likewise at their best?

   No: unripe fruits are usually at their least appealing. Green tomatoes, papayas and mangoes are eaten, but as vegetables: cut small for salads, cooked or pickled.

4. [The Making of Fruit: Ripening] Botanically, what is a fruit?

   The part of a plant that grows from the ovary of a flower, around the seeds. The ovary is the female part of the flower that holds the developing seeds. Most fruits are the thickened ovary wall. Apples and pears are an exception: mostly the swollen tip of the flower stem.

5. [The Making of Fruit: Ripening] Which three layers does a fruit usually have?

   A thin skin outside, a thin coat around the seeds, and a thick juicy layer between them.

6. [The Making of Fruit: Ripening] What are the four stages of fruit development?

   Fertilization Pollen fertilizes the ovule; growth hormones are released, and the ovary wall begins to expand. Example: seedless bananas, navel oranges and some grapes develop without fertilization. Cell multiplication A short stage in which the cells of the ovary wall divide. Cell expansion The cells fill with watery sap; most of the visible growth happens here. Example: a melon can grow by more than 80 cc (5 cubic inches) a day. Ripening The fruit becomes sweet, soft and aromatic; ripening end…

7. [The Making of Fruit: Ripening] As a young fruit swells, what do its storage cells fill up with?

   Watery sap, sugar, and defensive chemicals such as bitter alkaloids and astringent tannins. The sugar may be stored as starch. Fruit storage cells are among the largest plant cells: in watermelons they are almost 1 mm across.

8. [The Making of Fruit: Ripening] When is a fruit called mature, as opposed to ripe?

   When its seeds can grow on their own: the fruit is ready to start ripening. Ripening, which makes the fruit attractive to animals, comes after maturity.

9. [The Making of Fruit: Ripening] What changes happen when a fruit ripens?

   It gets sweeter and less sour, softens, loses its bitterness, gains aroma and changes color. Starch and acid decrease and sugars increase. The color usually goes from green to yellow or red.

10. [The Making of Fruit: Ripening] Is ripening the start of a fruit's decay?

    No: it is the last, intense phase of the fruit's life, controlled by the fruit itself. Because rotting follows soon after, ripening was long mistaken for the first step of breakdown.

11. [The Making of Fruit: Ripening] What carries out most of the chemical changes of ripening?

    Enzymes, which break big molecules into smaller ones and build new ones.

12. [The Making of Fruit: Ripening] How was the gas that triggers fruit ripening discovered?

    Around 1910, bananas stored near oranges ripened early, and green citrus near a kerosene stove colored faster. About twenty years later the common cause was found: ethylene, given off both by fruits and by burning kerosene.

13. [The Making of Fruit: Ripening] What is ethylene, in fruit biology?

    A simple gas that acts as a plant hormone: it triggers ripening. It works on mature but unripe fruit. Fruits make it themselves, so ripening starts in an organized way.

14. [The Making of Fruit: Ripening] What happens in a climacteric fruit when ethylene starts its ripening?

    The fruit makes much more ethylene itself, and ripens fast. Its respiration (oxygen use) speeds up 2 to 5 times. Flavor, texture and color change quickly, and often decline quickly afterwards.

15. [The Making of Fruit: Ripening] Why do climacteric fruits ripen well after being picked green, while nonclimacteric fruits do not?

    Climacteric fruits often store starch and turn it into sugar later; nonclimacteric fruits store little starch. So nonclimacteric fruits get no sweeter once picked; they need the plant to keep sending them sugar. They may still soften and gain aroma.

16. [The Making of Fruit: Ripening] Name some typical climacteric fruits (fruits that ripen fast in a burst of ethylene).

    Bananas, avocados, pears, tomatoes. These are picked hard, so they survive shipping, and gassed with ethylene at their destination.

17. [The Making of Fruit: Ripening] Name some typical nonclimacteric fruits (fruits that ripen only gradually on the plant).

    Pineapples, citrus fruits, most berries, melons. Their quality depends on how ripe they were when picked; nothing done afterwards improves it.

18. [The Making of Fruit: Ripening] How can you speed up the ripening of a hard pear or avocado at home?

    Close it in a paper bag with an already ripe fruit. The ripe fruit gives off ethylene gas, and the bag keeps the gas around the unripe one. A plastic bag would trap too much moisture.

19. [The Making of Fruit: Ripening] Tomatoes and peaches can ripen after picking. Are they still better ripened on it?

    Yes: on the plant they keep collecting the raw materials of flavor. Exceptions that ripen best off the plant: pears, avocados, kiwis, bananas.

20. [Common Fruits of Temperate Climates] What is a pome fruit, and which fruits are pomes?

    A fruit whose flesh is the greatly enlarged tip of the flower stem; apples, pears and quinces (rose family). The flower remains stick out at the bottom, and the few small seeds sit in a tough-walled core. The flesh of apple and pear comes from the receptacle (flower base); the ovary sits below the other flower parts, so the flower leaves a scar at the bottom.

21. [Common Fruits of Temperate Climates] Why should apples go into the refrigerator right after buying, but pears not?

    Apples are sold ripe; pears are sold unripe and need to ripen first. Ripen pears at cool room temperature, then refrigerate them unwrapped. Wrap apples and refrigerate them at once.

22. [Common Fruits of Temperate Climates] Where are an apple's antioxidants concentrated?

    In the skin. They are mostly simple phenolic compounds such as chlorogenic acid, which is also in coffee. Some apples have the antioxidant power of the vitamin C in 30 times their weight of orange.

23. [Common Fruits of Temperate Climates] Why can a lot of apple or pear cider upset the stomach?

    Apples and pears contain sorbitol, a sugar alcohol that we cannot digest. About 0.5% of the fruit. Undigested, it passes into the intestines, as with prunes.

24. [Common Fruits of Temperate Climates] Where did the eating apple originate?

    In the mountains of Kazakhstan. It came from crosses of a wild Asian apple with several relatives, spread early through the Middle East, and the Romans took it to the rest of Europe.

25. [Common Fruits of Temperate Climates] How do cooking apples differ from eating apples?

    Cooking apples are too tart raw, but taste balanced cooked and keep their shape in pies. Eating apples (about pH 3.4, 15% sugar) are crisp and balanced raw but rather bland cooked. Cooking apples: about pH 3, 12% sugar. Example: Bramley's Seedling.

26. [Common Fruits of Temperate Climates] Why are tannin-rich apples good for making cider?

    Tannins clump proteins and cell-wall bits together, so they settle and the cider clears. Together with high acidity, tannins also help keep the fermentation under control.

27. [Common Fruits of Temperate Climates] How can you quickly test whether an apple holds its shape when cooked?

    Bake a few slices wrapped in foil in a hot oven for 15 minutes. Or microwave them wrapped in plastic film until steam puffs the film up.

28. [Common Fruits of Temperate Climates] Why do apples taste milder after a few months of storage?

    They burn some of their malic acid for energy.

29. [Common Fruits of Temperate Climates] Why should apples and quinces be cooked with their skins on?

    Much of their aroma is made in the skin. The aroma-making enzymes are concentrated there.

30. [Common Fruits of Temperate Climates] Which compound gives cooked apple its typical aroma?

    Damascenone, a floral-smelling fragment of carotenoid pigments.

31. [Common Fruits of Temperate Climates] What is an ester?

    A molecule made by joining an acid and an alcohol. Many fruits owe their typical aroma to one or two esters.Example: ethyl alcohol + acetic acid = ethyl acetate.

32. [Common Fruits of Temperate Climates] How do fruits make their aromatic esters?

    Their enzymes join acids and alcohols that are already in the cells. The acids are tart acids of the cell fluid or fatty-acid parts of fats; the alcohols are by-products of the cells' chemistry.

33. [Common Fruits of Temperate Climates] Which ester gives each of these fruits its typical smell: apple, pear, pineapple, banana?

    Apple Ethyl acetate (ethyl alcohol + acetic acid) Pear Hexyl acetate (hexyl alcohol + acetic acid); also the "pear ester", ethyl decadienoate Pineapple Ethyl butyrate (ethyl alcohol + butyric acid) Banana Isoamyl acetate (isoamyl alcohol + acetic acid)

34. [Common Fruits of Temperate Climates] How much of an apple is air?

    Up to a quarter of its volume. The air sits in spaces between the cells. A pear is less than 5% air, so it is denser.

35. [Common Fruits of Temperate Climates] Why does an overripe apple feel mealy?

    Biting pulls whole cells apart instead of breaking them open, so no juice is released. The cell walls have softened and the cells have dried out. The many air spaces make it easy for the cells to separate.

36. [Common Fruits of Temperate Climates] Why does the skin of a whole baked apple often split?

    The air spaces in the flesh fill with expanding steam. Removing a strip of skin from the top lets the pressure out.

37. [Common Fruits of Temperate Climates] Why do apples make good jelly and thick applesauce?

    They are rich in pectin, the cell-wall material that thickens and gels.

38. [Common Fruits of Temperate Climates] What makes some apple juice cloudy rather than clear?

    Intact pectins and proteins floating in the juice, which scatter light.

39. [Common Fruits of Temperate Climates] What happens to fresh apple juice within about an hour of pressing?

    It starts to darken and its aroma changes, because enzymes react with oxygen. Bringing the juice quickly to the boil stops the browning enzymes, but gives it a cooked flavor.

40. [Common Fruits of Temperate Climates] What are Asian pears?

    Round pears with crisp, juicy, slightly gritty flesh, from China and Japan. They bruise easily, so they are often sold in protective foam sleeves.

41. [Common Fruits of Temperate Climates] What makes pear flesh gritty?

    Stone cells: hard cells with thick, cellulose-rich walls. All early pears were gritty "sand pears". Breeding reduced the stone cells; the soft "butter" pear was bred in 18th-century Belgium and France.

42. [Common Fruits of Temperate Climates] At what stage should pears be picked?

    Mature but still hard; they ripen best off the tree. Pears picked after ripening has started turn mushy, and their core breaks down. They ripen best slowly, over several days at 65 to 68°F/18 to 20°C.

43. [Common Fruits of Temperate Climates] Why should pears never be kept in closed plastic bags?

    Pears are sensitive to the carbon dioxide that builds up in the bag. They also respire faster than apples and do not keep as well.

44. [Common Fruits of Temperate Climates] What is a raw quince like, even when ripe?

    Hard, gritty and astringent.

45. [Common Fruits of Temperate Climates] What does cooking do to a quince?

    It makes it soft and mild. Heat breaks down the pectin-rich cell walls, and the astringent tannins bind to the cell debris instead of the tongue.

46. [Common Fruits of Temperate Climates] Why do quince slices turn from off-white to deep red when simmered in syrup for hours?

    Long cooking turns colorless phenolic compounds in the quince into red pigments (anthocyanins). Pears have the same compounds in smaller amounts (Bartletts about a twenty-fifth as much), so they turn pink at most.

47. [Common Fruits of Temperate Climates] What fruit was the original marmalade made from?

    Quince: Portuguese marmelada was a quince paste. Sour oranges took the quince's place later.

48. [Common Fruits of Temperate Climates] What is a bletted medlar?

    A medlar fruit kept for weeks after picking, until its own enzymes turn the flesh soft and brown. Bletting removes the astringency and the acid; the aroma gains notes of spice, baked apple, wine and gentle decay.D. H. Lawrence: "exquisite odour of leave-taking".

49. [Common Fruits of Temperate Climates] What are stone fruits?

    Fruits with a single seed inside a stone-hard shell: apricot, cherry, peach, plum. They belong to the genus Prunus (rose family).

50. [Common Fruits of Temperate Climates] Why are fresh stone fruits (peaches, plums, cherries) so seasonal?

    Their flesh turns mealy or falls apart in long cold storage. They store no starch either, so they gain no sugar once picked, though they still soften and develop aroma.

51. [Common Fruits of Temperate Climates] What chemical defense protects the seeds of stone fruits (peach, apricot, cherry)?

    An enzyme system that releases cyanide. The same system releases benzaldehyde, the smell of almond extract. Almonds are a stone fruit's seed too. So peach or apricot kernels give jams an almond note.

52. [Common Fruits of Temperate Climates] What gives fresh apricots their aroma?

    Terpenes (citrus, herbal and floral notes) and peach-like lactones.

53. [Common Fruits of Temperate Climates] Why are dried apricots usually treated with sulfur dioxide?

    To keep their orange color, vitamin C and fresh flavor. Unsulfured dried apricots turn brown and taste flatter and cooked. Their abundant pectin gives dried apricots a meaty texture.

54. [Common Fruits of Temperate Climates] Which compounds give cherries their flavor?

    Almond-like benzaldehyde, flowery linalool and clove-like eugenol.

55. [Common Fruits of Temperate Climates] Why is a French cherry clafoutis made with unpitted cherries?

    Baking cherries with their pits strengthens their almond and flowery notes.

56. [Common Fruits of Temperate Climates] What is left of the original fruit in a bright red industrial maraschino cherry?

    Little more than the cell walls and skin. The cherries are bleached with sulfur dioxide, stored in brine, soaked in syrup, dyed red, flavored with almond extract and pasteurized. Originally, marasca cherries were preserved in their own liqueur.

57. [Common Fruits of Temperate Climates] How are peaches and nectarines related?

    They are the same species; nectarines are smooth-skinned peaches. Nectarines are usually smaller, firmer and more aromatic. "Peach" comes from Persia, the route by which the fruit came west from China.

58. [Common Fruits of Temperate Climates] What is the difference between clingstone and freestone peaches?

    In clingstones the flesh sticks to the stone; in freestones it comes away easily. Firm clingstones were bred for canning, drying and shipping.

59. [Common Fruits of Temperate Climates] Which compounds give peaches their typical aroma?

    Lactones, which also give coconut its aroma.

60. [Common Fruits of Temperate Climates] What makes supermarket peaches mealy?

    Cold storage below about 45°F/8°C, which seems to upset the breakdown of pectin.

61. [Common Fruits of Temperate Climates] What gives prunes (dried plums) their rich flavor and dark color?

    Concentrated sugars and acids, plus browning reactions. Sugars are nearly 50% and acids 5% of the weight of prunes. The browning reactions give caramel and roasted notes and the brown-black color.

62. [Common Fruits of Temperate Climates] How do prunes keep ground meat from developing a warmed-over taste?

    Their antioxidants stop the fats from going stale, even at a few percent of the mix. About 1 tablespoon of prune per pound of meat. Their water-holding fiber and sorbitol also let them replace fat in hamburgers and baked goods.

63. [Common Fruits of Temperate Climates] What probably makes prunes a laxative?

    Sorbitol, a sugar alcohol we cannot digest: up to 15% of their weight. Undigested, it passes on into the intestines.

64. [Common Fruits of Temperate Climates] What are blueberries, raspberries and strawberries, botanically?

    Blueberry A true berry, from a single ovary. Raspberry Many tiny stone fruits from one flower. Strawberry A swollen flower base carrying tiny dry fruits on its surface. Blueberry, raspberry, strawberry.

65. [Common Fruits of Temperate Climates] What holds the tiny fruitlets of a raspberry together?

    Tiny tangled hairs on their surfaces, the original model for Velcro. One flower has 50 to 150 ovaries; each becomes a fruitlet with a stony seed, like a miniature plum.

66. [Common Fruits of Temperate Climates] Why is a raspberry hollow but a blackberry not?

    A raspberry slips off the flower base; a blackberry breaks off with the base inside.

67. [Common Fruits of Temperate Climates] Why do raspberries and blackberries spoil so fast?

    They respire faster than almost any other fruit, and their skin is thin.

68. [Common Fruits of Temperate Climates] What gives raspberries their typical flavor?

    Raspberry ketone, plus a violet-like note from ionones. Ionones are fragments of carotenoid pigments. Wild berries have by far the most intense flavor.

69. [Common Fruits of Temperate Climates] Why can blackberries turn red when frozen?

    Their anthocyanin pigments change color with acidity.

70. [Common Fruits of Temperate Climates] Why can blueberries in muffins turn green?

    Their anthocyanin pigments turn green with alkaline baking soda. Blueberries freeze well and keep their shape when baked.

71. [Common Fruits of Temperate Climates] Why do cranberries keep so well?

    They are very acidic and full of phenolic compounds, some of which kill microbes. Only lemons and limes are more acidic. One of the phenolics is benzoic acid, now a common food preservative.

72. [Common Fruits of Temperate Climates] How do cranberries help prevent urinary tract infections?

    A compound in them stops bacteria from sticking to the body's tissues. The compound is a precursor of pigments. Blueberries contain it too.

73. [Common Fruits of Temperate Climates] Why does barely cooked cranberry puree set into sauce at once?

    Cranberries are rich in pectin. Cranberries soaked in alcohol can even make the alcohol gel.

74. [Common Fruits of Temperate Climates] What is special about the aroma of black currants?

    It is very intense, with a musky, "catty" sulfur compound also found in sauvignon blanc wine. The French make black currants into the liqueur crème de cassis.

75. [Common Fruits of Temperate Climates] Which nutrients are black currants very rich in?

    Vitamin C and phenolic antioxidants (up to 1% of their weight). About a third of the phenolics are anthocyanin pigments.

76. [Common Fruits of Temperate Climates] Why has currant growing been restricted in the United States?

    Currants and gooseberries can carry a disease that attacks white pine trees.

77. [Common Fruits of Temperate Climates] Which aroma compounds make muscat grapes and Concord grapes smell different from other grapes?

    Muscat: flowery, citrusy terpenes. Concord: a musky ester (methyl anthranilate). Thompson seedless grapes have a fairly neutral, green aroma.

78. [Common Fruits of Temperate Climates] Why are raisins and dried dates brown?

    Browning enzymes act on phenolic compounds, and sugars react with amino acids. Both go faster when hot, so grapes dried in the shade give lighter raisins.

79. [Common Fruits of Temperate Climates] How are golden raisins kept light?

    The grapes are treated with sulfur dioxide and dried by machine under controlled conditions. Golden raisins taste fruitier and lighter than brown ones.

80. [Common Fruits of Temperate Climates] Why are Zante "currants" (tiny raisins) tarter than ordinary raisins?

    They are made from small Corinth grapes, which have more skin for their size.

81. [Common Fruits of Temperate Climates] What is verjus?

    The tart juice of unripe grapes, used like vinegar or lemon juice. The grapes are thinned from the vines 6 to 8 weeks before the main harvest.

82. [Common Fruits of Temperate Climates] What is saba?

    Ripe grape juice cooked down to a thick, sweet-tart syrup. Grape syrup was an important sweetener before sugar became cheap. Balsamic vinegar may have begun as grape syrup kept long enough to ferment.

83. [Common Fruits of Temperate Climates] How do kiwi fruits ripen?

    Slowly in cold storage, as their starch turns to sugar; then fast, in about 10 days at room temperature. Kiwis are picked full of starch and kept for months at 32°F/0°C. As they ripen, the flesh softens and fruity esters replace the grassy aroma.

84. [Common Fruits of Temperate Climates] Which two substances in kiwi fruit cause problems for the cook?

    Actinidin An enzyme that digests proteins: it damages other ingredients and can irritate skin. Heat inactivates it but dulls the color. Calcium oxalate crystals Needle-like crystals; pureeing or drying makes them more irritating to the mouth and throat.

85. [Common Fruits of Temperate Climates] A mulberry looks like a blackberry. How is it built differently?

    Each mulberry fruitlet comes from a separate flower; all of a blackberry's come from one flower.

86. [Common Fruits of Temperate Climates] What are the "seeds" on the surface of a strawberry?

    Tiny dry fruits (achenes), each with one seed inside. They are the same kind of fruit as sunflower "seeds".

87. [Common Fruits of Temperate Climates] What is the red flesh of a strawberry, botanically?

    The swollen base of the flower, not the ovary.

88. [Common Fruits of Temperate Climates] What keeps a ripe strawberry firm?

    The pressure of the fluid in each cell, pushing it against its neighbors. During ripening the inner cells enlarge and pull apart, leaving many tiny air pockets.

89. [Common Fruits of Temperate Climates] Why does a strawberry turn mushy after freezing?

    Ice crystals puncture the cell walls, so the cells lose the pressure that keeps the berry firm. Drying out does the same, by removing water.

90. [Common Fruits of Temperate Climates] Which compounds make up strawberry aroma?

    Fruity esters, caramel-like furaneol, and sulfur compounds. Furaneol is also in pineapple.

91. [Common Fruits of Temperate Climates] Why is pectin often added to strawberry jam?

    Strawberries contain little pectin of their own.

92. [Common Fruits of Temperate Climates] Where did the large modern garden strawberry come from?

    From an accidental cross of two American wild strawberries, in Brittany (France) around 1750. One parent was from Chile, one from North America. Its Latin name, ananassa, refers to its pineapple-like aroma.

93. [Common Fruits of Temperate Climates] Why should elderberries be cooked before eating?

    They contain lectins, harmful proteins that heat inactivates. Raw elderberries are also too tart.

94. [Common Fruits of Temperate Climates] Why are some persimmons (e.g. Hachiya) eaten only when soft as jelly?

    Until then they are full of astringent tannins. Nonastringent persimmons (e.g. Fuyu) can be eaten while still crisp.

95. [Common Fruits of Temperate Climates] How did the Chinese make unripe persimmons edible?

    They buried them in mud for several days. This may be the earliest form of controlled-atmosphere storage. Wrapping persimmons in oxygen-tight plastic film works the same way.

96. [Common Fruits of Temperate Climates] Why does keeping persimmons away from oxygen remove their astringency?

    Without oxygen the fruit makes acetaldehyde, which ties up the tannins inside the fruit. Bound tannins can no longer bind to the proteins of the tongue.

97. [Common Fruits of Temperate Climates] Why is American persimmon pudding black-brown?

    Hours in the oven with baking soda drive strong browning reactions. The fruit's sugars and the proteins of flour and eggs brown faster in alkaline conditions. With baking powder instead of soda, or a shorter bake, the pudding stays light orange.

98. [Common Fruits of Temperate Climates] Why can persimmon pulp be whipped into a lasting foam?

    Its tannins bind cell-wall fragments together, which holds the air bubbles in place.

99. [Common Fruits of Temperate Climates] Which part of the plant is rhubarb?

    The leaf stalks. The leaves (up to 1% oxalate, plus other chemicals) are said to be toxic.

100. [Common Fruits of Temperate Climates] What makes rhubarb so sour?

     Organic acids, 2 to 2.5% in total; about a tenth of the acidity is oxalic acid. That is 2 to 3 times the oxalate content of spinach and beets.