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.

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Space Candy & 3D-printed Candy

candy corn in space

In space, NASA astronaut Don Pettit uses candy corn for a zero-gravity candy corn demonstration that illustrates how surfactant molecules behave. In Germany, Café Gruen Ohr offers customers the chance to customize their own candy using a 3D printer.
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Nutmeg is a key note in October comfort favorites such as pumpkin spice lattes and spiced bread. The spice is warm, sweet, and spicy, perfect for the gradually colder days of autumn. Take a closer look at nutmeg, however, and you might find a disquieting surprise. Are you prepared to take a whiff of nutmeg science? Read more

The Keys to Cheese: Does This Cheese Melt?

Melted Cheese [Photo Credit: Pittaya Sroilong]

Melted Cheese Frize [Photo Credit: Pittaya Sroilong]

Whether you are making cheese fries, grilled cheese sandwiches, quesadillas, baked cheese bites, or homemade mac and cheese, choosing the right type of cheese can make or break these comfort foods. The key to all of these dishes is cheese that produces an even and homogenous melt. Cheeses like Cheddar, Mozzarella, and Gruyere are used often. If you aren’t feeling adventurous, you could just memorize the names of these greatest hits. However, if you want to experiment and change the melty cheese game, you’re going to have to understand why these cheeses work.

Let’s first examine what happens to cheese as it melts. The interactions of casein (milk proteins) and calcium help define its solid structure. When solid, caseins are bound together in large branching porous protein networks that entrap milkfat and water. Calcium (as calcium phosphate) acts as a bridge to stabilize these networks. When you apply heat to a cheese, melting occurs in two stages. First, at around 90 ˚F, milkfat is released1. This is because hydrophobic (water-repulsive) interactions between casein molecules increase under heat2. These interactions force out water molecules and the space between casein molecules increases allowing milkfat, which melts at this temperature, to escape. If you’ve put cheese on a burger that’s being grilled, you may see little sweat beads of liquid form on the cheese in the early stages of melting. The second stage happens at about 40 to 90 degrees higher, at around 130 – 180˚F3. At this point, the casein proteins do not break down, but rather, the increased movement of the proteins, resulting from the heat, allows for the proteins to act more fluid-like and the cheese melts.

There are many factors that control melting and explain why melting temperatures vary by as much as 50 degrees. No one factor defines a cheese’s melting properties as these factors can interact.

Moisture and Fat

Cheese with higher moisture and fat content tends to have lower melting points. For example, high moisture cheeses like Mozzarella melt around 130 ˚F and low moisture cheeses like Swiss melt at 150 ˚F 2. First, as previously highlighted, the milkfat and water portion of the cheese react to heat at lower temperatures than the proteins. Accordingly, with more moisture and fat present in a cheese, greater proportions of the cheese are susceptible to melting at lower temperatures. When the fat becomes liquid, it can no long provide support for the protein networks. Secondly, increased moisture and fat means that the casein proteins are more spread out and the mesh size (gap between proteins) is larger. This means there are fewer connections (bound calcium bridges) between proteins networks making melting more likely to occur at lower temperatures.

You may not know the exact moisture and fat content of every cheese variety without looking at a label, but intuitively, softer cheeses have more moisture and fat. Additionally, younger cheeses generally have more moisture so they also tend to melt more uniformly and evenly.

Acid Content

Chesses typically melt homogenously and evenly around a pH of 5.0 – 5.44. This is related to the calcium bridges. At too high a pH (pH > 6), too much calcium is present as bound calcium phosphate and the protein is too tightly bound to melt. With lowered pH, the calcium phosphate bound to the casein is replaced by hydrogen (H+), allowing for more movement among proteins.2 At around a pH of 5.0 – 5.4, there is a sufficient number of calcium present as bridges to allow for melting. At too low a pH (pH < 4.6), too many calcium bridges are lost and proteins aggregate and are unable to flow and melt evenly.

Lastly as a caveat, the factors being highlighted are specific to rennet-set cheeses, and not acid-set cheeses. Acid-set cheeses like queso fresco, paneer, and ricotta are not generally used, as they don’t produce even melts4. This results from the way they were made. In cheese making, you have two options for separating the solid curds (primarily casein proteins) and the liquid whey; Use rennet (an enzyme derived from the intestines or baby goats and cows) or use an acid (like vinegar or lemon juice).

When they are free floating in liquid milk, casein proteins have a slightly different molecular structure than when they are in cheese. In milk, caseins stick together in small clusters (micelles) that have negative charges on their surface. Since negative charges repel each other, these micelles won’t combine. Adding acid to heated milk lowers the pH, which neutralizes the negative charges on the micelles; therefore the casein micelles can aggregate. In contrast, using rennet to set cheese is a more targeted approach. In this process, an enzyme contained in rennet called chymosin, selectively removes negatively charged portions of the casein micelles and allows the micelles to clump.

In an acid-set cheese, calcium bridges are never formed as a result of the acidic environment used to generate the cheese5. These cheeses are only held together in protein aggregates rather than protein networks with calcium bridges and don’t produce the even melt desired.

Bottom Line:

Rennet-set cheeses with high moisture and fat are the best cheeses for melting as they melt evenly and consistently.

But don’t fret if you still want to harness the flavor of other cheeses (especially older or drier cheeses)! You have options: Try using a cheese blend with a higher proportion of the better melting cheeses and a small proportion of the other cheeses. For example, this recipe uses a 1:4 ratio. Experiment! You now know the keys for melty cheese!

References cited

  1. Schloss, Andrew and David Joachim. “The Science of Melting Cheese”
  2. Johnson, Mark. “The Melt and Stretch of Cheese”
  3. Mcgee, Harold. On Food and Cooking. 2004 “Cheese” (57 – 67).
  4. Tunick, Michael. The Science of Cheese. 2013 “Stretched Curd Cheeses, Alcohols, and Melting” (82 – 91).
  5. Sargento Food Service. “Cheese Melt Meter”
  6. Achitoff-Grey, Niki. “The Science of Melting Cheese”

Vince ReyesAbout the author: Vince Reyes earned his Ph.D. in Environmental Engineering at UCLA. Vince loves to explore the deliciousness of all things edible.

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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