Curious Cook in the New York Times: Organic produce and yak cheese

In today's Curious Cook column I write about nutritional claims made for organic fruits and vegetables and for yak cheese made in Nepal.

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Benbrook, C. et al. New Evidence Confirms the Nutritional Superiority of Plant-based Organic Foods. The Organic Center, March 2008.
http://www.organic-center.org/science.nutri.php?action=view&report_id=126

Or-Rashid, M.M. et al. Fatty acid composition of yak (Bos grunniens) cheese including conjugated linoleic acid and trans-18:1 fatty acids. J. Agricultural and Food Chemistry 2008, 56: 1654-60. http://dx.doi.org/10.1021/jf0725225

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.

Curious Cook in the New York Times: Potato chips

In today's Dining section of the Times I write about potato chips: the sounds they make, the music that has been made from them, and the forces that shape them.

My source for those shaping forces was Paul Green, a professor of plant biology at Stanford, and a friend. Paul died in 1998. In the column he became "Mr. Green." When I find a near-perfect chip and think of him, I don't think of Mr. Green, I think of Paul.

For helping me understand and explain the physics of chip shape, I thank two people who worked with Paul as postdoctoral fellows: Jacques Dumais of Harvard University and Sidney Shaw of Indiana University. Of course the simplifications and approximations are my doing, not theirs.

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Kim, S.-E. et al. Development of a method for the musical expression of cognitive food taste. Food Sci. Biotechnology 2005, 14, 738-42.

Zampini, M. and C. Spence. The role of auditory cues in modulating the perceived crispness and staleness of potato chips. Journal of Sensory Studies 2004, 19, 347-63.

Green, P. Transductions to generate plant form and pattern: An essay on cause and effect. Annals of Botany 1996, 78, 269-81.

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

Acrylamide: an update

Acrylamide is the industrially useful but toxic chemical that reared its ugly head among our potato chips and fries in 2002, when Swedish food chemists first thought to look for it in foods. Acrylamide is known to cause cancer and other illnesses in animals, and nerve damage in humans. It's suspected to be a human carcinogen as well. Acrylamide concentrations in drinking water are regulated by the Environmental Protection Agency, and the Swedish chemists found food levels hundreds of times higher than the EPA limit.

Since 2002, we've learned a lot about acrylamide in food. It's formed in both food manufacturing and in our kitchens during the heating of carbohydrate-rich foods (potatoes, grains and their products) at temperatures high enough to cause browning and the development of the desirable flavors typical of browned foods (above about 250 degrees F, 120 degrees C). It arises from the reaction of a particular amino acid, asparagine (the major amino acid in potatoes), with glucose and other sugars. Among the foods that contribute most to our daily intake of acrylamide are french fries and potato chips, breakfast cereals, cookies, and coffee. Breads, toast, pies and cakes, and corn snacks are also significant sources. Recently acrylamide was even detected in Japanese green teas, which contain asparagine and are finished by roasting at 250-280 degrees F, 120-140 degrees C.

Food chemists are coming up with a lot of new information about acrylamide levels in foods and ways to minimize them. Here are some recent findings.

A study from Donald Mottram and colleagues at the University of Reading shows that the addition of a little citric acid and the amino acid glycine reduces the acrylamide levels on cooked potatoes without reducing flavor.

Mottram and others have also found that the asparagine content of wheat flours, and their tendency to form acrylamide, depend strongly on the wheat variety, growing conditions, and farming methods. Inadequate sulfur nutrition can increase acrylamide production by a factor of 5. Less refined flours with more of the outer protein-rich aleurone layer produce more acrylamide, as do flours made from sprouted wheat.

Felix Escher and colleagues at the ETH in Zurich have found that during the last stage of potato frying, when the moisture content of the potato falls below 20%, the energy required for acrylamide production increases, while flavor production continues unaffected. This means that acrylamide levels can be minimized by lowering the oil temperature toward the end of the frying process.

What we don't yet know about acrylamide is the actual risk that it poses in our current diet. That bottom-line question is under active investigation by scientists in several countries. The fact that coffee consumption isn't associated with a higher cancer risk suggests to me that other protective factors in food compensate for its presence. But until we know for sure, it's prudent to go easy on fries and packaged snacks.

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Mizukami, Y., et al. Analysis of acrylamide in green tea . . . . J. Agric. Food Chem. 2006, 54, 7370-77.

Low, M.Y. et al. Effect of citric acid and glycine addition on acrylamide and flavor in a potato model system. J. Agric. Food Chem. 2006, 54, 5976-83.

Muttucumaru, N. et al. Formation of high levels of acrylamide during the processing of flour derived from sulfate-deprived wheat. J. Agric. Food Chem. 2006, 54, 8951-55.

Claus, A. et al. Influence of agronomic factors and extraction rate on the acrylamide contents in yeast-leavened breads. J. Agric. Food Chem. 2006, 54, 8968-76.

Amrein, T.M. et al. Influence of thermal processing conditions on acrylamide generation and browning in a potato model system. J. Agric. Food Chem. 2006, 54, 5910-16.

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

Curious Cook in the New York Times: Colorful garlic

In today's debut of my occasional column in the New York Times Wednesday food section, I write about the strange, blue-green colors that can develop when garlic and onions are handled in certain ways. The information in the column comes from several recent papers on the subject from labs in Japan and China. For readers who would like to follow up, here are a few (slightly confusing!) chemical details, and the references.

The reactions involve two special sulfur-containing chemicals from the garlic and onions, ordinary amino acids from both, and one enzyme from the garlic.

Step 1: the garlic enzyme alliinase converts the special garlic compound alliin (an allyl cysteine sulfoxide) to a pungent garlic flavor compound, allicin.

Step 2: the garlic enzyme alliinase also converts the special onion chemical (a propenyl cysteine sulfoxide) to two substances: the "lachrymatory factor" that irritates our eyes and has nothing to do with color development, and a colorless "color developer" (a propene thiosulfinate).

Step 3: this color developer reacts with an amino acid to produce a colorless "color precursor."

Step 4: the color precursor reacts with allicin to make the pigment molecules, the pyrroles, which range from reddish to green.

Because enzymes are inactivated at temperatures above 140 degrees F or so, moderate heat moderately speeds all these reaction steps, while high heat stops the first two steps and greatly accelerates the last two.

When freshly harvested garlic is stored at cool temperatures, it slowly accumulates alliin, the precursor to pungent allicin. Stored garlic thus gets progressively more pungent and more prone to developing color.



Bai, B. et al. Increase in the permeability of tonoplast of garlic by monocarboxylic acids. J. Agric. Food Chem. 2006: 54, 8103-07.

Ichikawa, M. et al. Changes inorganosulfur compounds in garlic cloves during storage. J. Agric. Food Chem. 2006: 54, 4849-54.

Imai, S. et al. Identification of Two Novel Pigment Precursors and a Reddish-Purple Pigment Involved in the Blue-Green Discoloration of Onion and Garlic.
J. Agric. Food Chem. 2006, 54, 843-847.

Imai, S. et al. Model Studies on Precursor System Generating Blue Pigment in Onion and Garlic. J. Agric. Food Chem. 2006: 54, 848-852.

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.

Green potatoes may not be as toxic as we thought

Beware of green potatoes, and peel every trace of green away: that's been standard advice for decades, and for good reason. When potatoes are exposed to light, these underground tubers interpret it as a sign that they're no longer completely buried in the soil. So they produce chlorophyll pigments to help them make use of the light's energy, and they produce bitter toxins to discourage animals from eating them. The toxins, alkaloids called solanine and chaconine, are about as powerful as their better-known cousin strychnine. They apparently interfere with the structure of all our cell membranes and also with the processing of a nerve transmitter (they inhibit acetylcholinesterase), which can cause hallucinations and convulsions. Because the color change in a potato parallels its accumulation of alkaloids, greenness is used as an indicator of toxicity and therefore irreversible spoilage. It's estimated that around 15% of the US potato crop is discarded on account of greening. But until recently, there has been little careful study of the toxin levels found in typical American potato varieties exposed to the light levels in typical markets.

N. Richard Knowles and colleagues at Washington State University exposed four different potato varieties (White Rose, Yukon Gold, Dark Red Norland, Russet Norkotah) to simulated store lighting for 10 days. They found that the correlation between color and alkaloid content was variable, with greening sometimes outpacing alkaloid accumulation. The highest alkaloid contents were found in the skins, where they sometimes exceeded the recommended maximum, an important fact for producers of potato-skin products. However, none of the varieties developed dangerous levels in the flesh.

These findings suggest that most greened potatoes need not be discarded. But the authors make two cautionary points. Potato alkaloids at low levels may have subtle toxic effects of which we're not yet aware. And because these alkaloids remain in the bloodstream for longer than 24 hours, people who eat potatoes every day may gradually accumulate toxic levels.

So it looks as though the occasional green potato is fine, but it's still not a good idea to buy them by the bagful.



Grunenfelder, L.A. et al., J. Agric. Food Chem. 2006, 54 (16), 5847.

Carotene pigments in mango and carrot

Mangoes and carrots are beautiful to look at because they contain rich deposits of carotene pigments. The carotenes come in many different variations, and range in color from yellow to deep orange. Beta carotene in particular is a valuable nutrient because it's an antioxidant, and because our bodies can convert it into vitamin A, which has important roles in our eyes and in other tissues. So we can count on orange-colored fruits and vegetables to be especially good for us. But often we don't get as much of their goodness as we might think.
Carotenes are much more soluble in fats and oils than in water. The cells of plants are mostly water, so the cells have to package the carotenes in special structures. One common structure is a solid crystalline mass. This is what carrot cells contain, and as a result, raw carrots give up a relatively small proportion of their carotenes. When we eat a raw carrot, the crystals only partly dissolve in the water-based mass of carrot, and only some of the carotene molecules are free for our intestinal cells to absorb. Cooked carrots are much more nutritious. The heating process disrupts the cells and carotene crystals, mixes the carotene molecules with other fatty materials in the carrot tissue and the rest of our meal, and makes them more readily available for absorption.
Mangoes are a different story. Reinhold Carle and colleagues at Hohenheim University recently studied mango cells and found that they store their carotene pigments not in solid crystals, but in microscopic oil droplets, where they are predissolved and so presumably much more available for our bodies to absorb them, even when we eat the fruit raw.
In a 2003 paper, Carle and colleagues reported that dried mangos are a concentrated source of beta carotene, even though the drying process does destroy some of the pigment. Sun-dried fruit suffer the greatest losses.

Vasquez-Caicedo, A.L. et al., J. Agric. Food Chem. 2006, 54 (16) 5769.