Strange flavors in white pepper

As I noted in my previous post, in this week's New York Times column I wrote about the recent discovery of the molecule that contributes the distinctive peppery aroma to black and white pepper--and to Syrah wines. Along the way, I also described some of the strange and not very pleasant aromas that white pepper can have, which range from barnyardy to plastic to medicinal. It was the plastic-medicinal quality that gave away the problem with some really bad pommes purées at a Midtown restaurant: they had been white-peppered to death.

In the printed version of the column, the third-to-last paragraph suggests that all white pepper carries these unpleasant notes. This is not true. You can find a corrected version of the column here.

Fresh peppercorns are small fruits. They consist of a large, light-colored seed surrounded by a thin fleshy layer, which turns from green to red as the peppercorn ripens. When the still-green peppercorn is harvested and dried, the outer layer turns black: hence black pepper. To make white pepper, the producers pick the peppercorns when they're ripe and the outer layer soft, put them into bags or barrels, and submerge them in water to ferment for as much as two weeks. The outer fleshy layer rots away, and the light seeds are then dried.

White pepper is valued by chefs and in food manufacturing for the fact that it provides pepper flavor without any unsightly little black specks. But the high incidence of flavor defects has been enough of a problem in the food industry that chemists in Germany set out to investigate it.

It turns out that the off-flavors develop during the fermentation. Pepper is grown and white pepper produced in the tropics, and thanks to the heat and the stagnant fermentation water, microbes flourish that break down peppercorn flesh to variations on the molecule indole and other compounds that smell rotten, fecal, cheesy, and chemical. The chemists showed that if the peppercorns are kept in constantly flowing water for just a few days, the fleshy layer can be removed with little or no development of off-flavors. This discovery should result in improved fermentation hygiene and more consistently clean-smelling white pepper.

In the meantime it's worth knowing that white pepper has this potential for carrying off-flavors. Taste it before cooking with it. Occasionally the funkiness can actually work. In hot-and-sour soup, for example, some recipes for which do specify white pepper, I find that it makes a positive contribution to all the commotion.

It's also interesting that according to the Australian study of the pepper aromatic, rotundone, white pepper contains more than twice as much rotundone as black pepper. This means that the same dose of white pepper will produce much more peppery aroma than black pepper. (At high doses, rotundone goes from smelling peppery to smelling harsh and burned.) Why should this be the case? Peppercorns for white pepper are harvested when the fruit is ripe, and it may be that rotundone levels go up as the fruits ripen.
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Steinhaus, M. and P. Schieberle. Role of the fermentation process in off-odorant formation in white pepper: On-site trial in Thailand. J. Agric. Food Chem. 2005, 53, 6056−6060.
http://dx.doi.org/10.1021/jf050604s

Curious Cook in the New York Times: Band-Aids, Shiraz Wines, and the Essence of Pepper

In this month's Curious Cook, I write about some really bad pommes pureés, the sometimes strange flavors of white pepper, and new research on Shiraz wines that revealed the key to pepperiness.

There's an error that crept into the printed column during the editing, and a number of interesting facts that didn't make the cut. More on these in my next post.
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Wood, C. et al. From wine to pepper: rotundone, an obscure sesquiterpene, is a potent spicy aroma compound. J. Agricultural and Food Chemistry, 2008, 56: 3738-44.    http://dx.doi.org/10.1021/jf800183k  

Curious Cook in the New York Times: Wild and crazy apples

In the November 21st issue of the New York Times, I write about rare and wild apples, and apples of the future.

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Curious Cook in the New York Times: Chemical signals that boost basil flavor

In today's Curious Cook column I write about the elusive flavor advantage of organic foods, and about a simple treatment that can increase the flavorfulness of basil and quite possibly other herbs and vegetables.


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P. Maeder et al., Wheat quality in organic and conventional farming: results of a 21 year field experiment. J. Science of Food and Agriculture, 2007, 87, 1826-35. http://dx.doi.org/10.1002/jsfa.2866


H.-J. Kim et al. Effect of chitosan on the biological properties of sweet basil (Ocimum basilicum L.). J. Agriculture and Food Chemistry 2005, 53, 3696-3701. http://dx.doi.org/10.1021/jf0480804

Curious Cook in the New York Times: Clarifying liquids with gelatin

In my column in the September 5 New York Times, I describe a recently discovered method for making intensely flavored liquid essences, or "consommés," from all kinds of foods, from meat stocks and fruit juices, baked potatoes and chocolate.

The Times prints a recipe for brown butter consommé from H. Alexander Talbot and Aki Kamozawa, authors of the remarkable blog Ideas in Food. David Kinch, chef-owner of the acclaimed restaurant Manresa in Los Gatos, California, generously sent me a recipe for a pumpkin consommé, but the the Times didn't have space to print it. With chef Kinch's kind permission, here it is.

Roasted dates with spiced pumpkin consommé
Adapted from David Kinch, Manresa Restaurant, Los Gatos California

For the consommé:

4 cups of pumpkin juice (approx. 4 small-med.sugar pie pumpkins, peeled, seeded and run through a juicer
1/2 t. grated nutmeg
1/2 t. ground cinnamon
4 cloves, ground fine
fresh ginger, square piece 1" in diameter, minced fine
1 cup, brown butter, strained
2 t powdered gelatin
Kosher salt, to taste
1 T. lemon juice


For the dates:

12 medjool dates
2 T. butter
2T. fino sherry
Slice toasted almonds
Olive oil
Creme fraiche


The day before:

Sprinkle the gelatin onto the surface of the pumpkin juice, and let stand for 5 minutes. Whisk together the pumpkin juice, the melted brown butter, the spices, a pinch of salt. Place the juices on medium heat and stir until the gelatin in completely dissolved.
Pour the juice into a shallow bowl, cover with plastic wrap and freeze solid. Line a strainer large enough to hold the frozen juice with cheese cloth. Place it over a larger bowl.
Pop out the frozen juice out of the bowl and place in the lined strainer. Allow the block to slowly melt in the refrigerator. It will take up to 24 hours. Dispose of the solids left behind in the cheese cloth.
Season the consommé with salt, lemon juice and a pinch of sugar.


The day of:

Preheat the oven to 350F.
Toss the the dates with 2 T. melted butter and the sherry. Roast in the oven in a baking dish uncovered baking dish until soft yet still maintain their shaped, approx. 1/2 hour. Set aside and allow to cool.
Place 2 roasted dates per person in 6 shallow soup bowl and pour the pumpkin consommé around. Garnish with a dollop of whipped creme fraiche and a drizzle of olive oil. Serve.

New developments in tomato flavor, part 2: How about some lemon basil in that tomato?

The second of two recent studies of tomato flavor involves genetic engineering, and offers a scent of tomorrow's tomatoes. 

A group of plant scientists in Israel and at Rutgers and the University of Michigan reported their success in transferring a gene from the basil plant into tomato plants. This particular gene diverts molecules in the pathway toward becoming the red pigment lycopene, and sends them instead onto the pathway that generates aroma molecules. The engineered tomato plants produced fruits that were paler than usual, but also had a stronger aroma and smelled distinctly of perfume, rose, geranium, and lemongrass. More than half of a panel of taste testers preferred the engineered tomato to its unengineered parent. 

This experiment may be a harbinger of things to come, a new era of plant modification in which flavor combinations once created by cooks will be re-created--or precreated--by breeders in the plants themselves. 

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Davidovich-Rikanati, R. et al., Enrichment of tomato flavor by diversion of the early plastidial terpenoid pathway. Nature Biotechnology 2007, online publication 24 June.
doi:10.1038/nbt1312

New developments in tomato flavor, part 1: Save the seeds

Two interesting studies of tomato flavor have appeared in the last month. One originated in the kitchen and may immediately change the way you taste and use tomatoes. The other involves genetic engineering, and offers a scent of tomorrow's tomatoes. Here's the first; check back in a few days for the second.

In classic French cooking, it's only the fleshy walls of the tomato fruit that get used in any kind of prominent way. The skin is peeled off and the seeds and their jelly are scooped out, perhaps to be used in a stock.

I've grown a number of different tomato varieties in my garden over the years, and in the course of comparing them in detail, found that I really liked the jelly more than the flesh. It has a wonderful slippery consistency, and it has more flavor. I thought that it was especially acidic and helped balance the sweetness of the flesh.

A few years ago, Heston Blumenthal at The Fat Duck near London tasted the seedy jelly of a tomato and was struck by what seemed to him a surprisingly intense umami taste, that savory, mouth-filling sensation created by MSG (monosodium glutamate, the sodium salt of glutamic acid) and several compounds called nucleotides. Heston maintains both formal and informal collaborations with several food scientists, and he asked Donald Mottram of the University of Reading whether there is more glutamic acid and nucleotides in the jelly than in the flesh. No one had asked the question before. So Professor Mottram's group did the analysis. The report has just come out, with Chef Blumenthal as a co-author.

Heston was right. The Reading group analyzed 14 different tomato varieties grown in a half dozen countries, and found that all of them had significantly higher glutamate contents in the jelly than in the flesh. The average ratio was nearly 4 to 1, and in some varieties was more than 6 to 1. The same general trend was found for several nucleotides, and for other free amino acids, which may contribute to the fullness of flavor. Though the salt content and pH weren't significantly different between jelly and flesh, the tasting panels consistently rated the jelly higher in perceived saltiness and acidity.

So: tomato jelly is packed with flavor. Taste it and use it! Several years ago at El Bulli in Spain, well before the Reading analysis, Ferran Adrià served clusters of tomato seeds and their jelly intact, as the central elements of a dish, to be admired for their glistening translucence and savored on their own. Why not?

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Oruna-Concha, M.-J. et al. Differences in Glutamic Acid and 5'-Ribonucleotide Contents between Flesh and Pulp of Tomatoes and the Relationship with Umami Taste. J. Agric. Food Chem. 2007, 55, 5776-80.
doi: 10.1021/jf070791p

Olive oil pungency and bitterness

Here are a couple of interesting details to add to the story of olive oil's back-of-the-throat, peppery pungency.

In 2003, a research group at Unilever reported on the sensory effects of several of the phenolic compounds found in olive oil, including the cough-inducing substance later named oleocanthal. Oleuropein, the phenolic compound that makes the fruit of the olive bitter, is water-soluble rather than fat-soluble, so it doesn't get transferred into the oil when the fruit is pressed. But a number of oleuropein relatives do end up in the oil, and the Unilever researchers tasted them in pure form. They found these compounds to contribute mainly bitterness and drying astringency, along with some numbing, cooling, sour, salty, and tingling sensations. Relatives of pungent oleocanthal also taste somewhat astringent and bitter. So an oil rich in phenolics can have a very complex taste and mouthfeel indeed.

Other studies have found that heating olive oil reduces the levels of most phenolic compounds. And pepperiness gradually fades as an oil ages. The balance of flavors in an excellent olive oil is thus temporary and so especially worth savoring when you find it. The deterioration of olive oil is slowed by keeping it cool and protected from light.

The balance of phenolics and of so of an oil's taste depends on the variety of olive, the way the oil is pressed and handled, and on the growing conditions for olive trees--especially the water supply. The olive tree is native to the arid Mediterranean and can get by with very little water. According to a number of recent reports, including one from the University of California at Davis, water stress produces very bitter and astringent olives, while copious irrigation produces olives and oils with very little bitterness, astringency, or fruity flavors. So the olive is another example of the many fruits and vegetables whose quality suffers when the plants are pampered.
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Andrewes, P. et al. Sensory properties of virgin olive oil polyphenols: identification of deacetoxy-ligstroside aglycon as a key contributor to pungency. J. Agric. Food Chem. 2003, 51, 1415-20.

Carrasco-Pancorbo, A. et al. Evaluation of the influence of thermal oxidation on the phenolic composition and on the antioxidant activity of extra-virgin olive oils. J. Agric. Food Chem. 2007, 55, 4771-80. http://dx.doi.org/10.1021/jf070186m

Berenguer, M.J. et al. Tree irrigation levels for optimum chemical and sensory properties of olive oil. HortScience 2006, 41, 427-32.

Curious Cook in the New York Times: Olive oil aromas and pungency

In today's Curious Cook column, I write about observing an olive oil competition, and about how one scientist's taste of a peppery oil led to the discovery of a natural version of ibuprofen.

One correction to the column: in the editing an important period got lost, and the result was to make Picual olive oil sound like a pretty miscellaneous collection of aromas. The printed paragraph is:

There were many different green notes pressed from the green fruit: of grass, celery, raw and cooked artichoke, green tea, seaweed. An oil from the Spanish picual variety smelled startlingly of tomato leaf, then green herbs: sage and rosemary and basil and mint and eucalyptus. From riper olives there were fruity and nutty aromas: citrus and almond and even banana.

It should read:

There were many different green notes pressed from the green fruit: of grass, celery, raw and cooked artichoke, green tea, seaweed. An oil from the Spanish picual variety smelled startlingly of tomato leaf. Then there were green herbs: sage and rosemary and basil and mint and eucalyptus. From riper olives there were fruity and nutty aromas: citrus and almond and even banana.

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The Los Angeles International Olive Oil Competition

Beauchamp, G. K. et al. Phytochemistry: ibuprofen-like activity in extra-virgin olive oil. Nature 2005, 437, 45–46.

Smith, A.B. et al. Synthesis and assignment of absolute configuration of (-)-oleocanthal: a potent, naturally occurring non-steroidal anti-inflammatory and anti-oxidant agent derived from extra virgin olive oils. Organic Letters 2005, 22, 5075-78.

Chilli pungency: A selective chemical weapon

The paper on chilli archaeology that I described a couple of days ago included two recent references that caught my eye, both by Joshua J. Tewksbury at the University of Washington, Douglas J. Levey of the University of Florida, and various colleagues. They add to our understanding of why it is that chillis evolved to accumulate the chemical, capsaicin, that makes their fruits pungent.

In one of those reports, published in November of last year, Levey, Tewksbury and colleagues tested the theory that capsaicin selectively repels rodents and other grain-eating mammals, which would chew up the chilli's seeds along with the surrounding fruit, while having no deterrent effect on birds, which have no teeth, swallow the fruits whole and defecate the seeds intact. They monitored wild chilli plants in Bolivia and in Arizona with video cameras, and found that only birds ate the fruits, as the theory predicts. Interesting sidelights: in past studies, lab rats frequently fed hot chillis have developed a strong liking for them, just as many humans do. And the wild species that were monitored, Capsicum chacoense and Capsicum annuum, bear fruits with a significant oil content, unlike our domesticated varieties. Oily chillis could be an interesting new ingredient.

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Levey, D.J. et al. A field test of the directed deterrence hypothesis in two species of wild chili. Oecologia 2006, 150: 61-68.
http://dx.doi.org/10.1007/s00442-006-0496-y

Ancient chillis

Spices and herbs are stimulants. Not necessarily pharmacological, but sensory: they stimulate our senses of taste and smell in foods that are otherwise bland. The human diet must have gotten a little boring when our ancestors first learned to cultivate grains and root crops and began to lean heavily on these starchy staffs of life, after millions of years of eating this and that as hunter-gatherers. So when did humans start spicing up their monotonous new diet? Very early--in the Americas, even before the widespread use of cooking pots, according to a new report on the archaeology of the chilli "pepper." A group of fifteen scientists led by Linda Perry of the Smithsonian Museum of Natural History published their results in this week's Science.

Chillis (species of Capsicum) originated in the Americas and are not related to the Asian black and other peppers (species of Piper). Perry and colleagues were able to identify ancient starch granules--"microfossils"-- from domesticated species of Capsicum, by their larger size compared to the starch granules of wild plants. Domesticated starch granules were found in settlements in Central and South America going back as much as 6,000 years. This is as old as the earliest possible date for the oldest known chilli macrofossils, fruits found in the Tehuacan Valley of Mexico. The most ancient sites are in what is now southwestern Ecuador, which is not thought likely to have been a center of chilli domestication, so the spice was probably domesticated elsewhere even earlier and brought there. The starch granules were found on grinding tools and in food remains along with evidence of maize, achira and arrowroot and manioc (starchy rhizome and root vegetables), squashes, jack beans, and palms. The scientists also found domesticated chilli starch in somewhat later sites across a wide region, from central Panama to the Peruvian Andes, Venezuela, and the Bahamas.

Say Perry and colleagues: "The presence of domesticated plants used as condiments rather than as staple foods during the Preceramic period indicates that sophisticated agriculture and complex cuisines arose early throughout the Americas and that the exploitation of maize, root crops, and chili peppers spread before the introduction of pottery."

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Perry, L. et al. Starch fossils and the domestication and dispersal of chili peppers (Capsicum spp. L.) in the Americas. Science 2007, 315, 986-88. http://dx.doi.org/10.1126/science.1136914

Rice: Scented and un-, old and new

Last week I wrote in the New York Times about the distinctive aroma of Himalayan basmati and Thai jasmine rices and the chemical that contributes it. I've collected several other interesting studies of rice over the last few months. They come from labs all over the world: not surprisingly Japan and Korea and Thailand, but also France, Switzerland, Italy, Belgium--and Arkansas. Here's some of their news; more tomorrow.


Rice Flavor: From Thailand, a study of the basmati/jasmine flavor molecule, 2-acetyl-1-pyrroline, 2AP for short, notes that 2AP is produced through the whole of the rice plant except for the roots. It's also found at very high levels in pandanus leaf, or screwpine (Pandanus amaryllifolius), an Asian herb that's often used to impart that same aroma to cooked dishes of various kinds. And in "bread flowers," flowers of Vallaris glabra, a tropical shrub, which form part of the traditional wedding potpourri in Malaysia. The Thai researchers found that the unmilled, brown fragrant rice had several times as much 2AP as it did after milling into white rice. And aged Indian basmatis had half the 2AP as fresh Thai jasmine. So you can get more intense basmati aroma from the brown rice and from newly harvested rice.


Rice texture: Interestingly, in the Himalayan region where basmati rice is produced, the people prefer their rice aged for several months--which apparently means that they lose some of the flavor for which basmati is prized. By contrast, Japanese consumers prize newly harvested rice, and don't like the cooking qualities of old rice. India and Pakistan prefer the grains to remain separate and firm, while Japan prefers them somewhat sticky and soft. As any rice sits for months, in the warehouse or in the kitchen cabinet, its cooked texture gets progressively firmer and less sticky.

These changes are probably the result of a number of factors, including the breakdown of grain oils into free fatty acids, which form very stable, hard complexes with starch molecules. A Japanese team looked at what happens to rice during storage, and found that normally dissolvable proteins at the rice surface become oxidized and undissolvable. They were able to reverse the increased firmness and decreased stickiness of the cooked texture by adding a chemical reducing agent, sodium sulfite, to the cooking water (to reverse the oxidation), or by abrading away the surface of the aged grain.

So apparently as a rice grain sits in storage, the surface proteins become oxidized, bond to each other, and form a thin skin on the grain, which limits water penetration into the grain, and limits the starch leakage outward that causes stickiness. That's at least part of the cause of the firmer cooked texture in aged rice.

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Sriseadka, T. et al. Rapid method for quantitative analysis of the aroma impact compound, 2-AP, in fragrant rice . . . . J. Agric. Food Chem. 2006, 54, 8183-89.

Ohno, T. and N. Ohisa. Studies on textural and chemical changes in aged rice grains. Food Sci. Technol. Research 2005, 11, 385-89.

Curious Cook in the New York Times: Of mice and wine, and rice

In today's dining section I write about the surprising connection between an obnoxious off-flavor in wines and the prized flavor of aromatic rices.

Check back in a couple of days for more news about rice.

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Snowdon, E. et al. Mousy off-flavor: A review. J. Agric. Food Chem. 2006, 54, 6465-74. http://dx.doi.org/10.1021/jf0528613

Salting tomatoes in the greenhouse

Tomato lovers know that a sprinkling of salt enhances the flavor of even the best field-ripened specimen. Some recent news that bodes well for improved flavor in greenhouse tomatoes: you can enhance tomato flavor by salting the plant as the fruit grows! At the Institute of Vegetable Science in Freising, German scientists grew hydroponic tomatoes in a solution that was 0.1% sodium chloride, about one-thirtieth the salinity of seawater. The plants produced fruits with significantly higher levels of flavorful organic acids and sugars, and as much as a third more vitamin C and beta-carotene (the precursor to vitamin A) and the antioxidant red pigment lycopene. The researchers don’t say whether the tomatoes were saltier than usual. They were smaller, so salting the growing medium may be the hydroponic equivalent of dry-farming, which restricts the availability of water to the plant and the dilution of flavor and nutrients.

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Krauss, S. et al. The Influence of Different Electrical Conductivity Values in a Simplified Recirculating Soilless System on Inner and Outer Fruit Quality Characteristics of Tomato. J. Agric. Food Chem., 2006, 441 -448. http://dx.doi.org/10.1021/jf051930a

In the dark: olive oil, milk, butter, and beer

In my last post I mentioned that olive oil is best stored in the dark. The same is true for milk and butter and beer. It's turning out that all these foods are sensitive to light for similar reasons.

When milk is exposed to light, especially sunlight or to the fluorescent lights in a market, it develops an unpleasant, sulfurous "sunlight" or "lightstruck" flavor. It's been known for a long time that the vitamin riboflavin is involved in this reaction, and a recent report by David Min and colleagues at Ohio State summarizes the current understanding of what happens. It turns out that the off flavor signals significant nutritional losses. When riboflavin absorbs certain frequencies of light, it catalyzes the conversion of ordinary oxygen to an especially reactive "singlet" form. Singlet oxygen in turn attacks the milk fat, producing fragments with grassy aromas, and it attacks the amino acid methionine, producing a compound with an overcooked-vegetable aroma (dimethyl disulfide). It also attacks both the riboflavin that made it, and vitamin D, which we need to absorb the calcium in milk efficiently.

Exposure to light also damages the flavor of beer, which accumulates a characteristic "skunky" sulfur compound known as MBT (3-methyl-2-butene-1-thiol). Earlier studies had shown that MBT is produced when flavor compounds from hops, the hop acids, react with sulfur-containing compounds. But the hop acids themselves don't absorb the wavelengths of light that cause skunkiness. It appeared that that the energy for the reaction was supplied indirectly, and probably by the same molecule that damages milk-- riboflavin! Richard Pozdrik and colleagues in Melbourne, Australia have strengthened the case against riboflavin by showing that light absorption by riboflavin in beer correlates well with the development of skunkiness.

According to a new study of butter done in Norway and Denmark, riboflavin isn't the only "photosensitizer" in dairy products. J.P. Wold and colleagues found that traces of chlorophyll and related substances in butter also absorb light energy and transfer it to other butter components, thus causing oxidation reactions and unpleasant flavor changes. This makes sense, because absorbing and transferring light energy is exactly what chlorophyll is designed to do in the leaf of a living plant. And it's the lovely green chlorophyll and related molecules that are the major photosensitizers in olive oil.


So it's a good idea to buy and keep all these foods in opaque or at least dark containers. If they're in clear glass or plastic, or the butter is wrapped in light wax paper, then keep them in the dark as much as possible.

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D.G. Bradley et al. Effects, quenching mechanisms, and kinetics of water-soluble compounds in riboflavin photosensitized oxidation of milk. J. Agric. Food Chemistry 2006, 54, 6016-20.

R. Pozdrik et al. Spectrophotometric method for exploring MBT formation in lager. J. Agric. Food Chemistry 2006, 54, 6123-29.

J.P. Wold et al. Active photosensitizers in butter detected by fluorescence spectroscopy and multivariate curve resolution. J. Agric. Food Chemistry 2006, 54, 10197-10204.

Kuerle fragrant pears

Last October I read a report about a kind of Asian pear that I'd never heard of--and then this last weekend I found it in the 99 Ranch Market in nearby Milpitas. It's different, delicious, and worth trying.

All European pears are varieties of the species Pyrus communis. Asian pears are varieties of one or two different species that have variously been called Pyrus pyrifolia, Pyrus ussuriensis, and now usually Pyrus serotina. Most of the Asian varieties grown in North America were developed in Japan, have crisp, juicy, off-white flesh, a round, apple-like shape, often a russet skin, and a distinctive aroma that to me seems both flowery and slightly alcoholic. Alcohol (ethanol) is in fact one of their characteristic chemical components. The flavor is refreshing and heady at the same time.

The Kuerle variety of Asian pear comes from China, mainly from the northwest near Xinjiang. According to scientists from Shihezi University in that city and colleagues at the China Agricultural University in Beijing, the Kuerle pear was developed more than a thousand years ago, and has been valued for its "super white" flesh, elongated shape, jade green skin, and special fragrance. Substantial quantities are now exported. The fruits are harvested when they've matured enough to contain about 12% sugars and organic acids in their cell fluids. By refractometer, my samples were indeed around 13%. They are small as pears go, around 3 inches /7.5 cm long, light green with a waxy feel to the skin, familiarly crisp and juicy like a Shinsui or 20th Century.

But the delicate aroma is different. My first bite reminded me immediately of bubble gum! Vintage 1960; I haven't had bubble gum in a while. Not nearly as heady and volatile as the usual Asian pear varieties, with a light, candy-like fruitiness that probably wouldn't work too easily with other ingredients, but that's charming on its own. The food scientists analyzed the Kuerle aroma and found several components that it has in common with European pears, including the characteristic European "pear ester" (an ethyl decadienoate, or a combination of an alcohol molecule with a ten-carbon fragment of a fatty acid). But to me the Kuerle was nothing like a Bartlett or Comice or Bosc. It's a distinctive addition to the flavors of autumn, if you can find it.

Chen, J.L. et al., Changes in the volatile compounds and chemical and physical properties of Kuerle fragrant pear during storage. J. Agric. Food Chem. 2006, 54, 8842-47.

Gleanings for Thanksgiving: turkeys and sweet potatoes

From a quick survey of recent advances in turkey science, it looks as though producers still have a lot to learn about processing their birds to give them the best cooking qualities--so that cooks have at least a fighting chance of making a tender, succulent roast.
After being slaughtered, eviscerated, and plucked, turkeys are generally immersed in chilled water to bring down their temperature rapidly and limit the growth of bacteria. The wet chill certainly improves the bird's shelf life. And by slowing down the enzymes that consume glucose for energy, it prevents the muscle cells from accumulating lactic acid and releasing fluid, a defect known as "soft exudative" meat.
But it also adds a substantial amount of water to the carcass, which makes it harder to crisp and brown the skin. And it also appears to eliminate the chance for the turkey's own muscle enzymes to tenderize and flavor the meat, as happens in the aging of beef. Scientists at Lincoln University in Canterbury, New Zealand found that rapid and prolonged chilling doesn't just slow down the tenderizing enzymes: it prevents them from acting at all. The result is "significantly tougher meat" than would be obtained if the enzymes retained some activity.
In the case of beef, cooks can compensate for inadequate aging by holding the meat for an hour or so at body temperature and giving the enzymes a chance to work much more rapidly than they can in a cold meat locker. This is one of the several benefits of cooking roasts slowly. But this kind of accelerated aging would be risky with chickens and turkeys, which have higher loads of bacteria both on the skin and in the body cavity: a temperature that encourages bird enzymes also encourages microbes. And it's not clear that the bird enzymes survive rapid and prolonged chilling.

So it's great to have more flavorful "heritage" turkeys making a comeback. Let's also figure out how to make them, and the rest of our birds, as tender and tasty as they can be.

F. Obanor et al. Effect of processing on turkey meat quality and proteolysis. Poultry Science 2005: 84, no.7, p.1123-1128.


Now a side dish. It may be that the sweetness which gives sweet potatoes their name involves more than just ordinary sugars. Chemists at the University of Naples have found that, in addition to being rich in maltose--a sugar made up of two glucose molecules--sweet potatoes contain unusual "aminoacyl sugars." These are molecules that combine a sugar (here sucrose, or table sugar) with an amino acid. In the past, chemists have synthesized similar molecules in the laboratory and found that some had a sweet taste. If the sweet-potato types do as well, then they may find use as natural and probably low-calorie alternatives to the sweeteners we now extract from cane, beets, and corn.

I. Dini et al., J Agric. Food Chem. 2006: 54, 16: 6089-93.

Black Tea: The Aroma of Oats and the Hottest Water

Black tea has one of the most complex aromas of anything we eat or drink. It starts out as simple, green-tasting young leaves; then the combination of enzyme action and heat generates hundreds of volatile molecules. Among the more prominent aromas are the flowery and fruity ones; roses, orange flowers, violets, apricots, and raspberries are in there, along with fresh-crushed leaves, dried hay, and caramel. German flavor chemists recently identified a previously unknown note: a molecule that also contributes to the characteristic sweet aroma of oats. Something for tea lovers to sniff for and enjoy.
In the course of their analysis, the chemists also discovered a new reason for the traditional practice of brewing black tea in a preheated teaot with water just off the boil. High-temperature brewing does the best job of extracting aroma compounds from the tea leaves, but it also generates even larger quantities of certain aromatics than were in the leaves to begin with! It may do so by breaking off small, aromatic portions from much larger molecules. By contrast, we brew green teas in water far below the boil (around 150 degrees F, 65 degrees C) to preserve their more delicate, simple aroma and color.
Schuh, C. and P. Schieberle, J.Agric Food Chem. 2006, 54(3) 916.

Cognacs contain more dissolved taste substances than other spirits

In a French study of the solids content of various spirits, cognacs and other brandies turned out to be more than 1% by weight polyphenols, carbohydrates, and caramel materials, all of which the spirits extract from the wood barrels in which they're aged. Armagnacs and rums contained about half the solids of cognacs, bourbons about a fifth, and whiskies a tenth. From 4 to 51 samples of each spirit were tested. These are large differences, and indicate that brandies should often seem more astringent, sweet, and full-bodied than their distilled cousins.

Picque, D. et al., J. Agric. Food Chem. 2006, 54 (15) 5220