Tag Archive for: food science

The International Year of Pulses


Photo credits: (flickr/Jessica Spengler)

The 68th United Nations General Assembly has declared 2016 the International Year of Pulses. [1] Pulses – that throbbing sensation of your carotid artery after a workout or during a first date, right? Nope. The UN suggests we celebrate the pulses that are leguminous crops harvested solely for their dry seeds. All lentils, and all varieties of dried beans, such as kidney beans, lima beans, butter beans and broad beans are pulses, as are chick peas, cowpeas, black-eyed peas and pigeon peas. Seeds that are harvested green, like green peas or green beans are classified as vegetable crops, not pulses. Legumes used primarily for oil extraction, like soybeans, are also not pulses. [2]

Why are pulses getting a year-long, world-wide campaign?

A global push for pulse production would address many problems of our global food system. The Food and Agriculture Organization of the United Nations’s campaign highlights these key benefits to pulse cultivation [1]:

  • Pulses are highly nutritious – they are excellent plant source of protein, and contain the B vitamins that our bodies require to convert food to energy
  • Pulses are economically accessible and contribute to food security at all levels – from farmers to consumers
  • Pulses foster sustainable agriculture, thus addressing agriculture’s role in climate change
  • Pulses promote biodiversity in agriculture


Now that we know the basics of pulses and why they’re important, let’s get scientific.


Photo credits: (flickr/Kelly Garbato)

Pulses in the nitrogen cycle

Pulses are legumes, or plants in the family Leguminosae. Thanks to their symbiosis with many members of the diazotrophic, or nitrogen-fixing bacterial genus Rhizobium that live in their roots and feed them with nitrogen from the air, pulses have a particularly high protein content compared to non-legumes. [3] Within the bacterium, atmospheric nitrogen (N2), which is typically unusable to plants, is converted to ammonium (NH4+) via the activity of the enzyme nitrogenase. The nitrogen of ammonium is converted to other more complex compounds that are beneficial to humans, like amino acids – the building blocks of protein. In exchange for fixing nitrogen, the bacterium receives food from the plant — carbon in the form of glucose (C6H12O6).


This remarkable bacterial symbiosis also enriches the soil in which pulses grow with nitrogen compounds like nitrite (NO2) and nitrate (NO3), which is the preferred nitrogen source for other green plants. For this reason, farmers who crop-rotate with legumes don’t need to apply nearly as much fertilizer as farmers who don’t. [3]

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Pulses in a changing climate

Many pulses are also hardy and drought tolerant crops – lentils, broad beans, peas, and chick peas are all native to the Fertile Crescent of the Near East, and have adapted to sprout quickly and reproduce in the rainy season before the hot, dry summer [3].

Anatomy of the pulse

All food seeds consist of three basic parts: an outer protective coat, the small embryonic portion that develops into the mature plant, and the storage tissue that feeds the plant embryo. [3]The bulk of the seed consists of storage cells are filled with particles of concentrated protein and granules of starch, or organized masses of starch chains.

Cooking and starch retrogradation

When we cook pulses, hot water permeates the starch granules. As the water molecules work themselves between the starch chains, the granules swell and soften. When the pulses later cool down, the starch chains bond to each other again in tighter, more organized associations, resulting in firmer granules. (This process is called retrogradation.) [3] Consider leftover lentils or beans: they’re always harder and drier the next day, and they never get quite as soft as when they were first cooked. This is because during the process of retrogradation, some starch molecules form granules that are even more tightly associated than the bonds in the original starch granule. They form small crystalline regions that resist breaking even at boiling temperatures. [3]

Retrogradation of starch might foil your plans for leftover lentils, but it does do our bodies good: Our digestive enzymes cannot easily digest retrograded starch, so eating it results in a more gradual rise in blood sugar compared to the effects of non-retrograded starch. [3] Our intestines need help breaking down this tough starch, and the beneficial bacteria in our large intestines are happy to be of assistance. Just as the diazotrophic bacteria in soil work in harmony with leguminous plants, our intestinal bacteria digests what we cannot. Thus the retrograded starch functions as a prebiotics, or food for the probiotic bacteria in our guts. Well-fed gut bacteria make for healthy digestive tracks and happy bowels.

Will this pulse promotion save the world and fix the global food economy? Perhaps. We can all do our part by making a hearty spinach dal for dinner tonight, and sweet red bean paste for dessert.


Works Cited

  1. “”Save and Grow in Practice” Highlights Importance of Pulses in Crop Rotations and Intercropping.” Pulses – 2016 | 2016 International Year of Pulses. Food and Agriculture Organization of the United Nations, n.d. Web. 05 Feb. 2016.
  2. “What Are Pulses? | FAO.” What Are Pulses? | FAO. Food and Agriculture Organization of the United Nations, 15 Oct. 2015. Web. 05 Feb. 2016.
  3. McGee, Harold. “Seeds.” On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner, 2004. N. pag. Print.

Elsbeth SitesAbout the author: Elsbeth Sites received her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

Read more by Elsbeth Sites

Maple Syrup

Photo credits: flickr/Doug

Photo credits: flickr/Doug

Nothing sets the tone for a drowsy Sunday afternoon like a breakfast that features maple syrup. This sticky and wonderful syrup fills the nooks and crannies of our nation’s waffles with the taste of autumn and the smell of Canada. Let’s take a moment to appreciate the science that makes maple syrup and its confectionery relatives the crown jewel of breakfast condiments.

Generally, syrups are made by extracting sap from plants and boiling them down so they become a more concentrated and viscous liquid. The sugar maple tree, Acer saccharum produces the sap that can eventually become maple syrup, as it produces sap in greater quantities than other maple varieties.


Optimal conditions for sap harvesting involve extreme temperature fluctuations from day to night. The northeastern United States and eastern Canada, of course, have just the night-day temperature shifts to produce quality maple sap. The traditional sap-seeker drills a small hole into the cambium, or woody tissue, of a maple tree, and inserts a spout. On warm days when temperatures are above freezing, the liquid sap expands and creates positive pressure in the xylem – the plant version of veins; this pressure pushes sap out of the tap hole and into the collection vessel. When night falls and temperatures drop below freezing, sap contracts as all liquids do when chilled. As the sap contracts, this creates negative pressure, which sucks water from the soil into the roots and the tree; this replenishes the sap that has bled out of the tap hole.

Photo Credits: flickr/Chiot's Run

Photo Credits: flickr/Chiot’s Run

After harvesting, the harvested sap is boiled down until it has a viscosity of about 150-200 centipoises – a viscosity very similar to that of motor oil. When the liquid has reached this consistency, it has undergone a 40x reduction in volume. The resulting syrup is approximately 62% sucrose, 34% water, 3% glucose and fructose, and 0.5% malic acid, other acids, and traces amounts of amino acids. The distinct and lovely aromatic notes of maple come from wood byproducts like vanillin, other products of sucrose caramelization, and products of Maillard reactions between the plant sugars and the amino acids.

Photo Credits: flickr/LadyDragonflyCC

Photo Credits: flickr/LadyDragonflyCC

Another delectable treat from Northern climates is maple sugar. Maple sugar is made by boiling maple syrup (which has a boiling temperature 25-40°F above the boiling point of water, but varies with altitude) to increase sucrose concentration, then letting the syrup cool. Left alone, the sucrose accumulates into coarse crystals that are thinly coated with the remainder of the syrup. Simply put, maple sugar is plain table sugar with a natural coating of maple flavor.

Photo Credits: flickr/cdn-pix

Photo Credits: flickr/cdn-pix

A luxury to smear on your toast or pancake, maple cream is surprisingly simple to make, and despite its name, doesn’t contain any dairy. This delicious creamy spread is a malleable mixture of very fine crystals that are dispersed in a small amount of syrup. Maple cream is made by cooling maple syrup rapidly to 70°F by immersing its container in ice water, then beating it continuously until it becomes very stiff; thereafter it is warmed until it becomes smooth and has the texture and viscosity of a runny buttercream frosting.

Photo credits: flickr/ Anne White

Photo credits: flickr/ Anne White

One last note on maple syrup – beware of imposters! If the bottle doesn’t say maple syrup, it is not maple syrup. Breakfast or pancake syrup disappointingly consists of corn syrup and artificial flavors.

Works Cited

  1. “Learn about the Science of Maple Syrup.” Cary Institute of Ecosystem Studies. N.p., 24 Mar. 2013. Web. 25 Nov. 2015.
  2. McGee, Harold. “Sugars and Syrups.” On Food and Cooking: The Science and Lore of the Kitchen. 1st ed. New York: Scribner, 2004. N. pag. Print.
  3. “Viscosity Comparison Chart.” Viscosity Comparison Chart. The Composites Store, n.d. Web. 25 Nov. 2015.

Elsbeth SitesAbout the author: Elsbeth Sites received her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

Read more by Elsbeth Sites


Photo Credit: flickr/Jazz Guy

Photo Credit: flickr/Jazz Guy

Around autumn, students, teachers, and parents may have some big decisions to make. Private school or public? AP calculus or Art History? What to pack for lunch? Often, the answer to that last question is a bologna sandwich. Bologna is the archetypal American sandwich meat – salty, moist, and a bit mysterious.

Bologna is a semisolid meat product made from one or more livestock sources, most commonly beef or pork, and may contain poultry meat. According to the Food and Drug Administration, “[Bologna] may not contain more than 30% fat or no more than 10% water, or a combination of 40% fat and added water. Up to 3.5% non-meat binders and extenders (such as nonfat dry milk, cereal, or dried whole milk) or 2% isolated soy protein may be used, but must be shown in the ingredients statement on the product’s label by its common name.”[1] In all, you can be sure that at least 45.5% of a given bologna is meat.

Photo Credit: flickr/Anne Mair Valentine

Photo Credit: flickr/Anne Mair Valentine

In most other deli meats, the source animal is somewhat apparent through the texture and flavor of the meat (think roast turkey or ham). This is not so for bologna, because the FDA requires that all bologna ingredients be comminuted, or reduced to minute particles so that no lard, collagen, or spices are detectable on the tongue. [1] Essentially, the result of comminution is a “meat batter” [1] Most bologna producers don’t reveal the particular spice blend they use, but typical pickling spices like black pepper, coriander, and celery seed will most likely be included, as well as myrtle berries.

A package labeled “Bologna with Variety Meats” can consist of no less than 15% of raw skeletal muscle meat with raw meat byproducts. [1] Byproducts in this case refer to non-skeletal muscle organs, like heart, kidney, or liver. Bologna of this nature must name the animal species said byproducts were sourced from, and be individually named in the ingredients list.

“Mechanically Separated” means that the meat product contains more than 150 milligrams of calcium per 100 grams of product, whereas a product that falls below this threshold can list the ingredient as “pork trimmings” or “ground pork”, for example. [1] Some calcium inevitably joins the meat via machinery that separates meat from bone, with incredible efficiency, called Advanced Meat Recovery (AMR). Bones contain both calcium carbonate and calcium phosphate, so the 150mg calcium maximum is intended to ensure bone particulate and dust are not present in the bologna. Through AMR, the bone is to remain intact while meat is scraped, shaved, or forced off through a sieve at high pressure. Pork and poultry may be processed in this way, but regulations do not permit human food to include mechanically separated beef — a precaution against Bovine Spongiform Encephalopathy, or Mad Cow disease.

Principles of Meat Science. 4th ed. Dubuque, IA: Kendall/Hunt

Principles of Meat Science. 4th ed. Dubuque, IA: Kendall/Hunt

The resulting pulverized/ground up, comminuted meat product is encased in a thin cellulose tube, ranging from about 0.025 mm to about 0.076 mm in thickness[3], which is manufactured from wood pulp. [2] They are engineered to have elastic properties similar to natural intestinal casings used for more traditional sausages. The inner surfaces can be coated with dye and smoke flavor that diffuses into the meat product, and antibiotics may incorporated into the casing to stifle bacterial growth. [2]

We can sing songs of our bologna’s names, we can contemplate the silliness of its pronunciation, but without some research it is difficult to discuss exactly what bologna is. Despite its enigmatic status, I hear it’s quite good when fried.



Works Cited

  1. United States. United States Department of Agriculture. Food Safety and Inspection Service. Hot Dogs and Food Safety. Web. 20 Oct. 2015.
  1. Aberle, Elton David. “Principles of Meat Processing.” Principles of Meat Science. 4th ed. Dubuque, IA: Kendall/Hunt, 2001.
  1. Nicholson, Myron D. Method of Making a Cellulose Food Casing. Viskase Corporation, Courtaulds Fibres Limited, assignee. Patent US 5277857 A. 11 Jan. 1994. Print.

Elsbeth SitesAbout the author: Elsbeth Sites received her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

Read more by Elsbeth Sites

Chocolate’s Future & Mysteries


In the town of Reading, located in Berkshire, England, exists the International Cocoa Quarantine Centre, where tropical cacao plants are kept to prevent the spread of pests and diseases which threaten the world’s chocolate supply. Over at Technische Universität München, physicists have shown that molecular simulations can solve how the chocolate-making process turns bitter cacao to sweet, silky chocolate on a molecular level.
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Structural Changes in Chocolate Blooming

Is there anything more disappointing than finding a chocolate bar in the back of the desk drawer, anticipating a tasty treat, then unwrapping the bar only to find a dull, grey haze has overtaken your dear candy? Seeing as bloomed chocolate is still edible, yes, there are many things more disappointing than that. But surely you’re curious about how chocolate that was once shiny and perfect came to be filmy and rough. Chocolate blooming, the process that produces the white-grey film that appears on the surface of an old chocolate, is due to molecular migration. More specifically, this imperfection is caused by the movement of fats to the surface of the chocolate followed by a subsequent recrystallization. In a paper published by Applied Materials & Interfaces, a team of researchers dedicated to keeping our chocolates blemish-free has clarified the precise mechanisms that cause chocolate blooming.

The main fat in chocolate is cocoa butter, which is solid at room temperature and melts at 37 degrees Celsius. The proportion of solid to liquid cocoa butter depends on the lipid composition, which depends on which specific triglycerides are present. The solid to liquid proportion also varies with the storage conditions of the chocolate.

As proposed by Aguilera et al, scientists who study this chocolate blooming, consider chocolate as a particulate medium of fat-coated particles such as cocoa solids, sucrose, and milk powder, all suspended in a fat phase with the aid of an emulsifier, which helps to mix fats and oils with water, which usually repel each other. There are six crystallographic polymorphs of cocoa butter molecules, that is, there are six ways the molecules can organize themselves. The structural stability of these polymorphs increases from 1- 6; form 1 is the best at forming solid butter at room temperature, while form 6 tends to arrange in the loose bonds of a liquid. Form 5 is the main form in chocolate, as it possesses the most aesthetically desirable properties. While the phenomenon of blooming is well known to result from melting and recrystallization of chocolate into a less desirable polymorph, it has been unclear how fat moves through the chocolate particle network: Does it move along the fat-particle interface? Does it diffuse through the fat phase (cocoa butter), or through the matrix of assorted particles?

Possible lipid migration pathways in chocolate - Reinke et al

Possible lipid migration pathways in chocolate – Reinke et al

In this experiment, researchers used synchrotron microfocus small-angle X-ray scattering to determine the preferential migration pathway of the cocoa butter molecules surrounded by three different soild components (cocoa solids, skim milk, and sucrose). This technique allows researchers to record the scattering of x-rays through a sample with defects in the nanometer range. They can then extrapolate information about the material’s macromolecules, their shapes and sizes up to 125 nanometers, and distances between partially ordered materials, such as pore sizes. For this experiment, this method is better than more traditional macroscopic techniques as the sample does not need to be dissected in order to examine it, therefore the same sample can be continually analyzed.

Sketch of the experimental setup - Reink et al

Sketch of the experimental setup – Reink et al

The researchers prepared and tempered four different chocolate samples. An initial scattering of x-rays and data collection was performed before the addition of sunflower oil, then 10 uL of oil was pipetted onto the chocolate surface, and a second scan was performed. Images of the droplet were captured through a high-speed camera. These scans were repeated at 5, 10, and 30 minutes after oil addition, and again after 1, 2, 5, and 24 hours.

The results obtained suggest that oil is migrating through pores and cracks in the solid structure driven by capillarity within seconds. This means that the oil can flow in narrow spaces in opposition to gravity. Then chemical migration through the fat phase occurs. The oil doesn’t traverse the fat-particle interface, nor does it move through the matrix of solid particles. This migration disrupts the crystalline cocoa butter, which induces softening.

Because the most immediate migration of oils occurs through the material porous structure, the formation of chocolate bloom could be prevented by minimizing pores and defects in the chocolate matrix. To prevent the longer-term effects of chemical migration of lipids, one must minimize the content of non-crystallized liquid cocoa butter. Tempering chocolate lends to crystalline structures that resist migration, as will reducing the liquid fat content. However, to ensure that you never encounter a sad hazy chocolate again, we recommend eating all chocolate goods expeditiously.

Works Cited

  1. Tracking Structural Changes in Lipid-based Multicomponent Food Materials due to Oil Migration by Microfocus Small-Angle X-ray Scattering. Svenja K. Reinke, Stephan V. Roth, Gonzalo Santoro, Josélio Vieira, Stefan Heinrich, and Stefan Palzer. ACS Applied Materials & Interfaces 2015 7 (18), 9929-9936. DOI:10.1021/acsami.5b02092
  2. Aguilera, J. M.; Michel, M.; Mayor, G.Fat Migration in Chocolate: Diffusion or Capillary Flow in a Particulate Solid?—A Hypothesis PaperJ. Food Sci. 2004, 69, 167–174


Elsbeth SitesAbout the author: Elsbeth Sites received her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

Read more by Elsbeth Sites

Freezer Burnt Meat

Photo credit: flickr/Steven Depolo

Photo credit: flickr/Steven Depolo

Freezing is an indispensable tool in modern cooking and eating. The biochemical processes that typically occur in meats cause decay, fat oxidation, and rancidity; the higher the temperature, the faster these reactions occur. Thus, we can largely thwart off these undesirable processes by keeping meat chilled. But tossing meat into the freezer rarely results in rainbows, sunshine, or perfect burger patties, because strangely enough we can also accelerate meat decay with cold. Freezer burn can take a beautiful filet mignon and turn its surface into a leathered, unappetizing slab.

Freezer burn is caused by water sublimation from ice crystals at the meat’s surface into the dry freezer air. Sublimation occurs when a solid substance undergoes a phase change and becomes a vapor without first passing through the liquid phase. The ice crystals on the meat surface sublimate, and leave behind tiny cavities. These tiny yet numerous cavities increase the surface area of the meat and expose more tissue to the air. This accelerates oxidation of fats, which causes the rancid flavors of old spoiled meat. We usually describe oxidized fats as simply tasting “off,” which is a vague term but seems apt if you’ve ever tasted lipids past their prime, perhaps by using shortening that has been in the pantry since you were a toddler.

Photo Credit: flickr/Marcus Ward

Here, solid ice crystals directly vaporize without first passing through the liquid phase. Photo Credit: flickr/Marcus Ward

In addition to the surface area increase caused by sublimation, the freezing process itself lends itself to fat oxidation. When the liquid water in meats crystallize in the cold, the concentrations of oxidizing salts and trace metals in the tissues increases. Unfortunately, oxidation can occur over time even in wrapped and frozen meats. Some oxygen will inevitably remain in contact with the meat, unless we create a vacuum seal.

Once meat has been damaged by the cold, there’s no undoing the oxidation. So either we plan our meals so that meats are cooked immediately after purchase, or we learn to prevent the sublimation that ruins both our pork chops and our days. We simply need to keep water crystals inside the meat and keep oxygen out. Using a vacuum sealer is our best bet for avoiding freezer burn, but for cheapskates like me who won’t shell out the $30 for the sealing device, a water-impermeable plastic wrapped tightly around the meat works well enough for most home chefs.

Thus meat is sealed away happily in plastic, free from villainous oxygen. Photo credits: flickr/Mike

Thus meat is sealed away happily in plastic, free from villainous oxygen. Photo credits: flickr/Mike

References cited

  1. McGee, Harold. “Meats.” McGee on Food & Cooking: An Encyclopedia of Kitchen Science, History and Culture. London: Hodder & Stoughton, 2004. N. pag. Print.
  2. “Sublimation.” The Columbia Electronic Encyclopedia. Columbia University Press, 2012. Web. 20 July 2015.


Elsbeth SitesAbout the author: Elsbeth Sites received her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

Read more by Elsbeth Sites

Alton Brown’s Jet Cream Ice Cream

Because you are currently reading a blog about science and food, there is a high probability that you have seen or at least heard of Alton Brown: host of Good Eats and about five other Food Network television shows. There is also a significant probability that you’re a mega-fan of Alton Brown, and if so, that’s something you and I have in common. I have been watching the bespectacled nerd-chef (I say that admiringly) since I was thirteen, and he has largely inspired my food science endeavors. On March 19th I had the absolute pleasure of attending Alton Brown Live! The Incredible Inevitable Tour in Napa, California.


Alton describes the show content as all the things he can’t do on TV, including stand-up comedy, live music, and most excitingly, showing off his insane kitchen inventions. Because even the thought of burning myself on MegaBake terrifies me, we’re going to work through the science behind his colder contraption: Jet Cream.

Making ice cream is usually a simple process. Once you have your cream mixture, it simply needs to be repeatedly cooled and agitated. If we simply froze ice cream base, we’d get huge ice crystals, which aren’t necessarily bad. Dessert shops like Blockheads and Chilly Ribbons sell “Snow Cream,” that results from shaving fine sheets from a block of frozen milk or cream. But if we want ice cream, as Alton clearly does, we must continually add air to the cream and disrupt the crystallization process to make tiny crystals that are barely perceivable on the tongue. That’s why ice cream is smooth and unctuous, while frozen milk is crisp and icy. Whether you’re shaking a container of cream surrounded by ice by hand or using an industrial ice cream machine, the goal is to keep ice crystals small.

Alton’s goal is no different. To make ice cream, all he needs to do is simultaneously freeze and agitate his chocolate cream. His Jet Cream machine is an extravagant way to do a huge batch all at once, and in less than ten seconds. Rather than use ice and salt in a bason like pioneers did, or use liquid nitrogen like the modern gastronome, he uses compressed carbon dioxide via fire extinguisher.

When the fast-flying molecules of carbon dioxide gas are compressed into the extinguisher, they are stored at a very high pressure, typically 825 pounds per square inch. [1] A fire erupts on the stove, or you have a sudden urge for ice cream, so you pull the lever. The pressure is released; the gas flies out, and the nozzle and surrounding air become extremely cold, as tends to happen when a  gas suddenly expands from a high pressure to a low pressure. The change in temperature divided by the change in pressure makes a ratio (∆T/∆P) known as the Joule-Thomson coefficient.[2] The nozzle and surrounding air are chilled because the gas’ pressure change occurs too quickly for significant heat transfer to occur. For many gases at room temperature, as the CO2 in the extinguisher is, the ∆T/∆P ratio is positive, so a pressure drop is accompanied by a temperature drop. The molecules that were once speeding around inside the canister are now so low-energy that they form solid CO2, or dry ice. Dry ice is much, much colder than regular H2O ice because carbon dioxide freezes at -109 degrees Fahrenheit, while water freezes at 32 degrees. [3] Colder temperature = faster crystallization = quicker ice cream.

Photo Credit: David Allen, The Eater

Photo Credit: David Allen, The Eater

Now for the agitation: At the other end of Alton’s Jet Cream contraption is a typical water fire-extinguisher filled with chocolate cream. When this lever is pulled, a high-pressure spray of chocolate ensues. Between the two extinguishers are office water cooler jugs that act as the reaction chamber for the CO2 and cream. If the two levers are pulled exactly at the same time (synchronicity is very important in avoiding a catastrophic mess, stresses Alton), the blasts of cold and cream will collide in the coolers, providing the continual disturbance of the freezing process, as well as the incorporation of air, necessary to make tiny tasty ice crystals.

After plunking a scoop into a sugar cone and applying a generous coat of rainbow sprinkles, Alton hands off his creation to his volunteer assistant and asks if it is not the best ice cream he has ever had. Volunteer assistant replies that it is “So good.”

So there you have it. If you want ice cream that is “so good,” and you want a gallon of it fast, Jet Cream is the contraption for you.


Photo credits: instagram.com/altonbrown/

Photo credit: instagram.com/altonbrown/

References cited:

  1. “CO2 Fire Extinguishers.” Fire Extinguisher Guide. N.p., n.d. Web. 06 Apr. 2015.
  2. Joule Thomson Effect.” Wright State University – Department of Chemistry.  N.p., n.d. Web. 06 Apr. 2015
  3. “UCSB Science Line.” UCSB Science Line. N.p., n.d. Web. 06 Apr. 2015.

Elsbeth SitesAbout the author: Elsbeth Sites is pursuing her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food. Read more by Elsbeth Sites

Physiology of Foie Gras

Photo Credits: (flickr/Ulterior Epiculture)

Photo Credits: (flickr/Ulterior Epicure)

Decadent, diseased, silky, sinful. The adjectives that follow foie gras range from the disgusting to the luxurious. The fattened liver of a duck or goose polarizes people, and there seems to be no middle ground wherein a person can both enjoy foie gras and ethically question it. Because it is such a controversial food, the discourse surrounding it is often steeped in emotion, but the best way to make an informed, fact-based decision is through science. Here we will examine physiology, pathology, and a bit of genetics regarding waterfowl and foie gras in an attempt to promote overall awareness of what we eat (or don’t eat).

Foie gras is French for fatty liver, and that is exactly what it is. The liver of a bird, usually a duck or sometimes a goose, that has been force-fed to the point of having a fat, enlarged liver. The liver must weigh more than 300g for ducks, and 400g for geese to legally bear the name foie gras in France. [1] Force-feeding is typically done through a practice called gavage, wherein a long tube is inserted into the bird’s mouth and throat up to three times a day for 3-10 days. French rural code L654-27-1 states that “Foie gras belongs to the protected cultural and gastronomical heritage of France.”[2] Currently, the farming of animals to produce foie gras is banned in 22 EU nations, but not its sale or import. In California, the sale of foie gras was banned in 2004, the ban was lifted in early 2015 by a federal court, and the lifting of that ban is currently being appealed. [3] Needless to say, it’s a very complicated issue.

Photo Credits: (flickr/Pickled newt)

Photo Credits: (flickr/Pickled newt)

Foie Gras Physiology

Many bird species, including ducks and geese, eat prey much wider than the diameter of their esophagus. Consequently, the inner diameter of the upper part of the esophagus is comparatively larger than in mammals. [4] Also unlike mammals, the upper esophagus is not circled by cartilaginous rings, which explains how birds swallow whole, live fish with ease. In humans, the upper esophageal sphincter is a high-pressure zone situated between the pharynx and the cervical esophagus. The sphincter is composed of muscle, cartilage, and bone, [5] and thus is much more rigid than the upper esophagus of a waterfowl. Most birds species posses an “outpouching” of the esophagus, known as the crop. It also allows the birds to store large amounts of food before sending it along to the stomach for digestion. [4]

Another important difference in human and duck anatomy is the trachea. In humans, food and air start along the same path in the mouth, then the trachea (or windpipe) branches off at the back of the throat where the epiglottis prevents food from entering the trachea and channels swallowed food along its proper route, the esophagus. Try to force something past the epiglottis, and you trigger the unpleasant pharyngeal reflex, or gag reflex. Certainly a gavage would trigger this in a human, which is one reason why images of force fed birds make us so uncomfortable. Foie producers say if the procedure is carried under proper conditions, the gavage does not block the upper respiratory tract as the birds’ tracheas and esophaguses are completely separate, [6] and thus they do not gag or feel discomfort as a human would. However, foie gras critics rebuke that this is a ridiculous excuse, and that the birds are clearly harmed by the gavage.

Ducks and geese are sometimes reported to be panting when observed in a foie-farm. But before we assume they do so because they’re in distress, we should keep in mind that like a dog, panting in birds is a thermo-regulatory reflex. [4] Humans have sudoriferous glands (sweat glands) that discharge sweat to take care of latent heat, but birds do not. They regulate body temperature by opening their beaks and panting to cool down. Researchers have examined whether other avian behaviors are indicators of distress, like avoidance behavior, elevated heart rate, or elevated cortisol (stress hormone) levels. They report that force-feeding does not stress the birds more than typical capture and handling does. [1] [Side note: Most of this research was conducted by the same group of scientists from the French National Institute for Agricultural Research, so it would be helpful to have experiments performed by more organizations.]

Photo Credits: (flickr/Jeremy Couture)

Photo Credits: (flickr/Jeremy Couture)


In mammals, hepatic steatosis (fatty liver) is a pathological condition. Human fatty liver occurs when there is an imbalance of fat uptake and export in the liver, most often caused by alcoholism, malnutrition, obesity, or diabetes. On its own, hepatic steatosis is not harmful and can be reversed, but if not addressed with dietary and lifestyle change it can develop into cirrhosis, wherein the healthy liver tissue is replaced by scar tissue, or necrosis (tissue death). Indeed, foie gras in a human is a disease. [7]

Certain metabolic adaptations in migratory birds and fish cause a natural hepatic steatosis, and proponents of foie gras use this observation to argue that the condition is not pathological in those species. These animals must compile large energy stores for their migrations, and they do so by ingesting carbohydrates and storing the energy as fat, a process called lipogenesis. [8] Foie producers posit that they are simply exploiting the incredible lipogenetic abilities of the fowl liver. The human liver does no more than 30% of our entire bodies’ lipogenesis, as our adipose tissue carries most of the workload. [9] By contrast, the avian liver performs the vast majority of their lipogenesis, up to 96% of it in some species. [10] To further their argument that their birds are not diseased, foie farmers assert that it is in their best interest to avoid producing diseased livers, as they are of no commercial value.

Photo Credits: (flickr/Jay Tong)

Photo Credits: (flickr/Jay Tong)

Genetics of the Muscovy Duck

In addition to the anatomical and physiological aspects of waterfowl that may make the production of foie gras seem less cruel, a look into the breed may provide further insight. Foie gras is made from the liver of the Moulard duck, which is the product of a female Pekin artificially inseminated with the sperm of a male Muscovy duck. [1]The Moulard, or “mule duck” genotype is not present in the wild, and like other hybrid species, it is sterile. Therefore, the animals themselves cannot breed more baby Moulards.

Muscovies are non-migratory, [11] so unlike migratory species, in natural settings they do not gorge themselves to put on extra fat to carry them through long periods of physical exertion with no breaks to replenish energy. It might seem like they would be a poor choice for duck farming, but they are prized for their well-flavored, lean meat.

Pekin ducks on the other hand have many of the characteristics of migratory species. They are naturally gregarious and clump themselves together whether or not they have space to roam. [11] Years of breeding have made them very plump and small-winged, and thus they no longer migrate. However, their inner organs and basic metabolism still maintain characteristics of migratory waterfowl. The moulard thus exhibits the more desirable behavioral features of the two species. Like muscovies, they have no migratory instincts, so they are easy to farm-raise. But they retain all of the anatomy and metabolism of Pekins that naturally make them want to gorge and store energy as fat.

Photo Credits: (flickr/Taylor149)

Photo Credits: (flickr/Taylor149)

In this physiological context, gavage and foie gras might not be as tortuous as some imagine it to be. Even with this information, some people may still feel uncomfortable with the idea of force-feeding, and that is perfectly reasonable. If we want to eat foie gras entirely guilt-free, perhaps we should support the production of “humane” foie gras, where the animal is left to gorge on its own as if it were preparing for migration. Examining foie gras through a scientific lens teaches us to evaluate the animal body for its natural capabilities, but science does not always give us clear answers as to what is morally right. Regarding foie gras, the jury is literally still out.

References Cited

  1. Guémené, Daniel, Gérard Guy, Jérôme Noirault, Nicolas Destombes, and Jean-Michel Faure. “Rearing Conditions during the Force-feeding Period in Male Mule Ducks and Their Impact upon Stress and Welfare.” Animal Research 55.5 (2006): 443-58. Web.
  2. “Legifrance – Le Service Public De L’accès Au Droit.” Code Rural Et De La Pêche Maritime. N.p., n.d. Web. 19 Feb. 2015
  3. McClurg, Lesley. “The Legal Battle Over Foie Gras Continues.” – Capradio.org. Capital Public Radio, 9 Feb. 2015. Web. 19 Feb. 2015.
  4. Guémené, Daniel, Gérard Guy, Jacques Servière, and Jean-Michel Faure. “Force Feeding: An Examination of Available Scientific Evidence.” Artisan Farmers Alliance (n.d.): n. pag. Artisanfarmers.org. Web.
  5. Kuo, Braden, and Daniela Urma. “Esophagus – Anatomy and Development.” GI Motility Online (2006): n. pag. Web.
  6. http://onlinelibrary.wiley.com/store/10.1111/j.1740-8261.1991.tb00087.x/asset/j.1740-8261.1991.tb00087.x.pdf?v=1&t=i5inm4hl&s=a129cb6b04b350dfd5778a83eaaea1f2f0fb02a0
  7. Jaeschke, Hartmut, Jaspreet S. Gujral, and Mary Lynn Bajt. “Apoptosis and Necrosis in Liver Disease.” Liver International 24.2 (2004): 85-89. Web.
  8. Pilo, B., and J.c. George. “Diurnal and Seasonal Variation in Liver Glycogen and Fat in Relation to Metabolic Status of Liver and M. Pectoralis in the Migratory Starling, Sturnus Roseus, Wintering in India.” Comparative Biochemistry and Physiology Part A: Physiology 74.3 (1983): 601-04. Web.
  9. Timlin, Maureen T., and Elizabeth J. Parks. “Temporal Patterns of De Novo Lipogenesis in the Postprandial State in Healthy Men.” The American Journal of Clinical Nutrition 18.1 (2005): 35-42. Web.
  10. Desmeth, M., M. Messeyne, G. Schuermans, J. Vandeputte-Poma, and F. Vandergeynst. “Effect of Age and Diet on the Fatty Acid Composition of Triglycéridesand Phospholipids from Liver, Adipose Tissue and Crop of the Pigeon.” The Journal of Nutrition 111 (1980): n. pag. Web.
  11. Lopez, Kenji. “The Physiology of Foie: Why Foie Gras Is Not Unethical.” Serious Eats. N.p., 16 Dec. 2007. Web. 18 Feb. 2015.

Elsbeth SitesAbout the author: Elsbeth Sites is pursuing her B.S. in Biology at UCLA. Her addiction to the Food Network has developed into a love of learning about the science behind food.

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How We Taste

How We Taste

Featuring Dr. Dana Small, Chef Wylie Dufresne, & Peter Meehan

May 14, 2014 

As part of our 2014 public lecture series, we explored the concept of taste from the perspectives of a scientist, a chef, and a food writer. Dr. Dana Small described how our brains respond to flavors. Chef Wylie Dufresne of Wd~50 presented his creative approach to generating surprising food flavors and textures.  Peter Meehan shared his experiences with food and taste and how they have shaped his writing, both as a cookbook author and former writer for The New York Times.

Check out the highlights or watch the full lecture below

Wylie Dufresne on Science in the Kitchen and It’s Impact on WD~50

“Cooking is a lot of things and one of the things we discovered was that cooking is a science. There’s certainly some biology. There’s certainly some physics. There’s an awful lot of chemistry at play all the time when you’re cooking… One of the main reasons I opened up WD~50 … was to create a space where I could continue my culinary education, where my staff could continue their culinary education, and where you as a diner, if you so choose, could continue your culinary education.”

Wylie Dufresne on his Aerated Foie Gras 

“How could we, using some very modern technology, walk the idea of a mousse down the road? … Part of the problem with a mousse is that it usually has a lot of stuff in it besides the main ingredient… So what we wanted to do was to figure out if we could create a mousse of foie gras, or if we could aerate foie gras without adding or taking too much away from the flavor.”

Peter Meehan on Developing Taste and Eating Everything

“The first step in developing the taste to become a restaurant critic: Eat … I tried to just each everything… the more I ate the more I understood about food and the more I could draw connections about one thing and another… You start to make these mental points on a map of where flavors are in relation to each other.”

Dr. Dana Small Defines Taste

“There’s molecules and ions in the foods that we eat and they bind to cells on these elongated taste receptors [tastebuds]. When enough binds, the cells get excited. They send a signal to the brain that the brain then interprets as a taste … Taste evolved to detect the presence of nutrients and toxics … You’re born knowing that you like sweet and dislike bitter … because you don’t want to have to learn that sweet is energy and bitter is toxin.”

Dr. Dana Small Defines Flavor and How It’s Different from Taste

“Flavor, on the other hand, preferences and liking for flavors is entirely learned. This has the advantage of allowing us to learn to like available energy sources and learn to avoid particular food items … The flavor allows us to identify a particular item that was associated with a particular consequence that we need to remember… whereas the taste provides just a signal about whether an energy source as in the case of sweet is present.”

Watch the Entire Lecture

Deconstructing Twinkies & Sonicating Gummi Bears

Dodo twinkies

The Twinkies ingredients list is analyzed to figure out how these snacks have such a long shelf life (45 days!), while in lab, gummi bears are subjected to sonication, liquid nitrogen, and trypsin.
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