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You Asked: Can coffee explode in the microwave oven?

coffeeA sensational sounding e-mail about “exploding coffee” has been making the rounds. It describes the misadventures of an unfortunate soul who heated up water for coffee in a microwave oven. When he picked up the mug, it “exploded!”

Explode is probably too strong a term, but spurting and frothing is a real possibility. This is due to a phenomenon known as superheating. First, we have to understand what boiling is all about. At the surface of a liquid molecules are always evaporating. If we leave a glass of water out, it will eventually disappear.  If we heat the liquid, its molecules move faster, become more energetic and more molecules go into the vapour phase. As a consequence, the liquid disappears more quickly. At the boiling point, molecules all over the liquid, not only at the surface are energetic enough to go into the vapour phase. They do this most readily by evaporating into airspaces that exist in the container. All containers have imperfections where air gets entrapped when a liquid is introduced. As these air pockets fill with vapour, they expand and begin to rise. That is why we see streams of bubbles which originate at the sides or the bottom of the container.

In a microwave oven, the container is not heated, only the water.  So the container actually cools the liquid in contact with it, meaning that the liquid in the center is always hotter, sometimes by as much as 10 degrees C. But the liquid in the center cannot boil, because there are no air bubbles for it to evaporate into.  By the time the liquid near the edge of the container reaches the boiling point, the liquid in the middle is considerably hotter; it is superheated.

The addition of sugar or a tea bag now can spur vigorous boiling. This is because the surface imperfections introduce trapped air bubbles into which the superheated liquid vaporizes. Sometimes just picking up the container can have an explosive effect as the superheated liquid comes into contact with air bubbles on the periphery. Accidents can be prevented by putting a plastic spoon into the mug or glass while it is heating in the microwave. In this case the scare-mongering note about “exploding coffee” may actually has some basis in fact.

Joe Schwarcz PhD

You Asked: What is natamycin?

natamycin“The customer is always right,” is a time-honoured adage in marketing. It holds true even if the customer is wrong. If the customer does not want “artificial” preservatives” in food, industry will comply, whether that move is supported by science or not. Of course no company wants to poison its customers, so eliminating preservatives is a risky business. What’s the answer? Look for a “natural” preservative. That will satisfy the consumer who has a disdain for anything artificial, and at the same time will reduce the worry for the producer about marketing an unsafe product.

Kraft, for example, has announced that, at least in the U.S., it will be replacing artificial preservatives with natural ones in its cheese products. This boils down to not much more than a question of semantics. Sorbic acid and its salts, the “artificial” preservatives that have been used, are to be replaced by natamycin, an antifungal compound produced by soil bacteria. Although many cheeses are actually mould ripened, with blue cheese being the classic example, cheese is also prone to infection by a variety of rogue moulds that can cause spoilage. Sorbic acid and its salts can prevent the growth of moulds, yeast and fungi, even when used at concentrations of less than 0.1%. It was back in 1859 that Professor August Wilhelm Hofmann first isolated sorbic acid by distilling the oil obtained from the berries of the rowan tree. This is the same Professor Hofmann who was enticed to England by Prince Albert to head up the newly created Royal College of Chemistry and who essentially founded the synthetic dye industry.

So, doesn’t the fact that sorbic acid can be isolated from berries make it a “natural” substance? Yes. And I suppose there would be no clamoring to remove it from food if this is how it were produced. But distilling sorbic acid from rowan berries is not an economical process and would not do for the estimated 30,000 tons needed every year by the food industry. But sorbic acid can also be readily produced by a number of synthetic methods, including the reaction of crotonaldehyde with ketene, both of which can be made from compounds isolated from petroleum. This synthesis is economically viable and is the way that sorbic acid is produced. Any chemical is defined by its molecular structure which does not depend on the route by which it was produced. The sorbic acid produced by the rowan berry is identical to the sorbic acid produced by chemical synthesis, but because the latter was not extracted from a natural source, it is termed “artificial,” and therefore in the eyes of some people, suspect. The fact is that sorbic acid, irrelevant of the source, is a food additive that has passed all the regulatory hurdles just like its replacement, natamycin.

Natamycin is an antifungal agent produced by a soil bacterium that was first found in South Africa’s Natal province, hence the name. Since bacteria occur in nature, any of the chemicals they crank out can be classified as “natural.” But curiously a substance that occurs in nature, like sorbic acid, is termed an artificial preservative when it is synthesized in the lab. Natamycin may be natural, but it would not be so appealing to people if they knew they were eating the waste product of dirt bacteria. Not that there is anything wrong with that.

Joe Schwarcz PhD

You Asked: Why does a cooked onion taste sweet and how come cutting a cooked onion does not make the eyes water?

onionOnion chemistry is extremely fascinating and extremely complex! We’ve been intrigued by this vegetable ever since our prehistoric ancestors gathered and cooked wild onions. By the time of the First Egyptian Dynasty 5000 years ago, onions were widely consumed for flavor and for their supposed medicinal properties. At various times they have been associated with the prevention of colds, loosening of phlegm, correction of indigestion, inducement of sleep, stimulation of appetite, disinfection of wounds and the elimination of parasites from the digestive tract. In ancient times people believed that onions were a symbol of eternity because of the concentric circles that make up their structure. For this reason, onion shaped towers became popular in Russia and Eastern Europe; the idea was that these buildings would stand forever.

Onions may not make us live forever but some of their components may indeed have medical benefits in reducing cholesterol, blood pressure and perhaps even the risk of cancer. This is why their chemistry has received a great deal of attention. The smell produced by a cut onion is actually a form of chemical warfare the plant has evolved to ward off pests. When an insect attacks the bulb, tissue damage unleashes a sequence of chemical reactions resulting in the release of propanethial oxide, an irritating substance designed to repel the attacker. This reacts with moisture in the eyes to form sulphuric acid which is the stuff that makes our eyes water. Unfortunately, to the onion, attack by an insect or a sharp knife appears to be the same.

Frying the onion causes yet another reaction, resulting in the formation of bispropenyl disulfide which has a sweet smell and a sweet taste. Some of the harsher tasting compounds are also destroyed by the heat, explaining the change in flavor. Furthermore, we do not cry over cooked onions because heat destroys the enzymes that are needed for the formation of propanethial oxide. Also the cooking process drives off any volatile irritants.

 

Joe Schwarcz PhD

You Asked: Is it true that they add cyanide to salt?

saltYes, sort of. Some commercial varieties of salt have small amounts of sodium ferrocyanide added to prevent caking. When humidity is high, a thin layer of moisture forms on the surface of the salt crystals, and some of the salt dissolves in this layer to form brine. If the relative humidity then drops, the water evaporates and the brine solution recrystallizes between the salt crystals, causing them to aggregate into clumps. Ferrocyanide decreases the solubility of salt in water so the salt is less likely to dissolve in the moisture that coats the crystals and that in turn reduces the amount of recrystallization.

Any mention of cyanide conjures up images of poison so the presence of ferrocyanide in salt sounds scary. That’s why producers would rather list it on a label as “yellow prussiate of soda,” an old-fashioned term first coined in reference to Prussia, the country where it was originally synthesized. There is, however, no need to be terrified of ferrocyanide because the cyanide in this compound is tightly bound to an iron atom and is not released in the body. Even if it were, it would be irrelevant because the amount would be way too little to cause any harm. And ferrocyanide itself is remarkably non-toxic.

 

Joe Schwarcz

You Asked: Why does a barber’s pole has a red stripe?

barber poleIt represents the colour of blood. During the Middle Ages monks were required to shave the crown of their head, a function commonly performed by itinerant barbers. Also, under ecclesiastic law, monks had to be periodically bled. This was supposedly a symbol of piousness, of devotion to God.
Barbers began to attend to this duty as well. They would travel with a “flag” of a white cloth dipped in blood to indicate that they would attend to anyone who needed to be bled. This early mode of advertisement eventually was transformed into the barber’s pole. And the pole began to symbolize more than haircuts and bleeding. Barbers began to expand their role and became quasi surgeons, specializing in sewing up wounds and extracting teeth. They also dabbled in the whitening of teeth by dabbing them with nitric acid. This did produce an immediate whitening, but destroyed the teeth in the long run by wearing away the protective enamel.
But at least one 16th-century barber surgeon, Ambroise Pare, made an important contribution to medicine. Barbers in those days worked under the guidance of physicians, who thought themselves above menial jobs like cutting and scalding. Why scalding? Because physicians thought that gunpowder was poisonous and therefore gunshot wounds had to be treated with boiling oil to destroy the poison. Unfortunately, if the bullet didn’t kill the victim, the scalding often did.
During the siege of Turin in 1537 Pare ran out of oil and for some reason substituted a cold mixture of egg yolks, oil of roses, and turpentine. To his surprise, the soldiers treated with this mixture fared better than those who had been scalded. And thus ended the brutal practice of pouring hot oil into bullet wounds. The French-trained Pare was a religious sort, and thought he had had help in making his observation. That’s why he introduced the oft-repeated phrase, “I dressed the wound, but God healed him.”

Joe Schwarcz

You Asked: Should we be concerned about parabens in cosmetics?

parabensNot if you look at the numbers. Many cosmetics now advertise “no parabens,” as they cater to chemical paranoia. Parabens are very effective preservatives and prevent bacterial growth in creams and lotions. The reason that they have made news is that they have estrogenic activity. But the fact is that this activity by comparison to the body’s natural estrogen is essentially insignificant, some 10,000 times less. Based on studies carried out with animals, the no observed adverse effect level (NOAEL) has been determined to be about 800 mgs per kg of body mass. The NOAEL is the maximum amount that can be given on a regular basis without causing any effect. This means that a 70 kg person would have to apply 55 grams of parabens regularly to have an adverse effect, assuming that it is all absorbed when applied to the skin, which of course is not the case. And how much cream does this translate to? Given that the most parabens used as a preservative makes up about 0.8% of the weight of a lotion, a quick calculation shows that about 70 bottles each containing 100 mL each would have to be applied to the skin every day to approach the NOAEL. Basically, parabens “toxicity” is a non-issue. And not that this is of any relevance, but parabens occur in nature. They are found in blueberries as well as in the secretions female dogs use to attract males.

Joe Schwarcz

You Asked: Is it True That People Who Drink Tea Live Longer Longer ?

teaDrink tea to live longer? Newspaper headlines may have said that, but, that is not exactly what the study they were referring to said. Nevertheless it is an interesting study, published in the American Journal of Clinical Nutrition, a highly respected peer-reviewed publication. The study evaluated intake of flavonoids in an elderly Australian female population through food frequency questionnaires. Flavonoids constitute a huge class of compounds found in plants, members of which are linked through a basic molecular structure they share. The reason for interest in these compounds is that laboratory experiments have shown possible anti-allergenic, anti-inflammatory, anti-cancer,-anti-heart disease and antioxidant effects. Although, there is a dearth of studies in people using isolated flavonoids, it is generally assumed that the benefits ascribed to eating fruits and vegetables may be due to their flavonoid content.

One way to get a handle on possible flavonoid benefits is to see if there is any connection between estimated flavonoid intake and health status. The best measure of health status is longevity. Two data bases of flavonoid content of foods were used to estimate intake of these compounds in the diets of over a thousand women with an average age of 80 who were followed for five years. Indeed, subjects who consumed the most flavonoids, 800 mgs or so a day, lived longer than women whose intake was less than 500 mgs whether the eventual cause of death was cancer or heart disease. In this population the major source of flavonoids was tea, about 350 mg for two cups, but there is no reason to believe that flavonoids in tea are in any way different from those found in berries, onions, bananas, cocoa, wine, citrus fruits, parsley or peanut skins. What all these have in common is that they are plant products, so this study reinforces the notion that our diet should be mostly plant based.

There are the usual caveats with such a study, the classic one being that an association cannot prove cause and effect. Although attempts were made to correct for confounders such as body weight and physical activity level, it is still possible that other components of the diet that parallel flavonoid intake are responsible for the noted difference in longevity. Then there is the usual problem that food frequency questionnaires may not accurately reflect food intake because of memory and honesty issues. But if flavonoids are really players in the good health game, which is likely, it is interesting to note that the average North American intake is only about 300 mgs which is considerably less than that of the longest lived subjects in this study. For a ballpark idea, an apple, a cup of blueberries or a cup of tea are all in the 150 mg flavonoid content range. So while tea may not be the elixir of life, a couple of cups a day are an easy way to increase flavonoid intake. There is no downside. Unless you load it up with sugar as is the case with many canned and bottled teas. Make your tea at home, add a dose of lemon juice if you like, but leave out the sugar. It may not make you live longer but it will make life a little more pleasant.

 

Joe Schwarcz

You Asked: Is it true that dogs are being poisoned by propylene glycol in some dogfoods?

dog foodNumerous Internet posts attempt to scare dog owners with questions like “Is It a Dog Food Aide or Automotive Antifreeze?” The reference is to propylene glycol, a chemical added to some dog foods to help retain moisture. Of course being an antifreeze component and serving as a food additive are not mutually exclusive. After all nobody worries about eating salt because it is also used in enemas. The potential risk of a substance is determined by studying it, not by making specious associations.

So what do the studies say? Unfortunately when it comes to dogs, not a whole lot. In humans, propylene glycol when ingested is pretty innocuous. Toxicity occurs when blood concentration reach 4 grams per liter, which is unachievable by consuming foods or beverages that contain the chemical. And yes, it is used in human food, mostly to retain moisture, although it also serves as a solvent for flavours. The pharmaceutical industry uses propylene glycol as a solvent in formulations of drugs that are insoluble in water. In beer it can stabilize head foam, in soft drinks and flavoured coffees it carries flavour, it stabilizes whipped cream and prevents the formation of crystals in ice cream.

Canada attaches no numerical value to the maximum amount of propylene glycol that can be used as long as it conforms to “good manufacturing practices.” In the U.S., it can be used up to 50 grams per kilogram of food or beverage. Europe allows maximum of 3 grams per kilogram. The reason for the discrepancy is not clear since there is no evidence that amounts greater than the European limit cause any problem. But this difference between amounts allowed in Europe and the U.S. did cause quite a kerfuffle when Fireball Whisky was recalled in Norway, Sweden and Finland. It seems the American version of the product found its way across the ocean with levels of propylene glycol above those acceptable in Europe.

This precipitated a public outcry in Europe where people recalled with horror the 1985 episode when some Austrian wines were adulterated with diethylene glycol, another chemical that can be used in antifreeze, to make the wines sweeter and more full-bodied in the style of late harvest wines. Nobody was hurt except the Austrian wine industry which suffered an almost complete collapse.

The publicity about the Fireball recall in Europe bounced back to the U.S. where this whisky is a popular choice among the college set due to its low cost and relatively high alcohol content. Rumors that a Fireball recall was underway sent ripples of upset across social sites.There was no recall, but as expected the chemophobes rallied around the “they’re putting antifreeze into our food” battle cry. The fact is that someone would perish from alcohol poisoning long before enough alcohol were consumed to cause a problem with propylene glycol.

Exactly why propylene glycol is found in Fireball whisky isn’t clear. The company goes no further than to say that “the secret to Fireball is buried in the depths of our souls and it’s so damn special that we just can’t share it. Although we’d love to talk Fireball, we have a strict policy that we let our whisky speak for itself.” In all likelihood propylene glycol is used as a solvent for some flavour that is added to the whisky.

While there is no issue with propylene glycol in human food, dogs may be a different case. They often eat the same food for all their meals and the continued ingestion of propylene glycol even in small doses may conceivably be a problem. That is just what a class action lawsuit launched by a California pet owner contends. He claims that two of his dogs got sick and one died after he began to feed his pets with “Beneful” produced by Nestle Purina Dog Care. The lawsuit describes over 3000 complaints on line about dogs developing liver problems, kidney failure, seizures and diarrhea due either to propylene glycol or ochratoxin, a fungal metabolite found in the food.

The manufacturer dismisses the notion that Beneful is the cause of the ailments. Dogs get sick, and owners then look for a cause, with food being a prime suspect, they say. And Beneful is not associated with symptoms any more than any other dog food, whether it contains propylene glycol or not. However, whether that is indeed the case is hard to know. Nobody it seems has actually done a study. Given that propylene glycol is known to be toxic to cats, causing “Heinz body anemia,” and since questions have been raised about its effects on dogs, it may be prudent to choose varieties of dog food that do not contain the chemical.

Joe Schwarcz PhD
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