When cooking an egg, you often notice that the egg white (albumen) changes from a clear, runny liquid, to a firm, opaque, solid. Why does this happen? Similarly, why does yellow, unbaked bread dough, turn brown when put in the oven? These questions are answered in a branch of food science called molecular gastronomy. While this two-word phrase may seem intimidating, it simply refers to the study of the physical and chemical changes that happen to ingredients during cooking. The term was created by Hervé This and Nicholas Kurti in 1988 as the title of a series of workshops aimed at exploring the science behind the cooking of ingredients. The pivotal moment in molecular gastronomy came in 1969, when Kurti held a presentation called “The Physicist in the Kitchen” for the Royal Society of London, in which he performed food-based science experiments, including making meringue in a vacuum chamber (previously unheard of since meringue involves beating air into egg whites) and using pineapple juice to digest protein. In this blog post, we will explore three major applications of molecular gastronomy: spherification using alginate, transglutaminase meat glue, and sous-vide cooking. As will be seen, understanding the chemistry behind food allows for exotic and unique culinary creations to be realized.
Spherification with Alginate
One of the great wonders of molecular gastronomy is the process of reverse spherification, which allows one to create balls of liquid encapsulated in long-lasting, gelatinous shells, similar to caviar. How exactly does spherification work? The secret lies in the chemicals involved.
The first of two main components is alginate, which can be extracted from brown seaweed. Alginate is an anionic polysaccharide, and is often obtained as a sodium salt. It is important to know that alginate is not the only compound capable of performing the same role, as chemist and food enthusiast Martin Lerschasserts – a whole list can be found here. The large carbohydrate chains of alginate allow it to act as a thickening agent, but the real magic happens when the second of the main components is present – calcium ions. In contrast to alginate, it is preferred that the calcium ions already be present in the liquid being spherified. In the case that calcium is not already present, calcium lactate or calcium lactate gluconate can be added. What exactly happens between the alginate and the calcium ions that allows for the formation of liquid-filled spheres? The calcium ions fit between the strands of alginate, allowing them to interlock, creating a net of tangled polymers and form ing a gel. After knowing the chemistry behind spherification, the process is quite simple – the flavored liquid, containing calcium ions, is simply “dropped” using an eyedropper into a solution of sodium alginate.
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| Left: Alginate, Right: Calcium lactate gluconate |
However, before spherification can be guaranteed to happen, there is one parameter left to tweak – density of the flavored liquid. This physical property is extremely important due to surface tension, the net effect of the intermolecular forces between liquid particles at the surface. An underly dense liquid will not be able to penetrate the surface of the sodium alginate solution, while an overly dense one will not bead up into a sphere.
Spherification has had many creative applications to molecular gastronomy over the years. A popular experiment is to encapsulate tiny drops of fruit juice, creating “fruit caviar.” However, using larger drops allows one to also simulate many foods, like green olives and cheese.
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| Various examples of spherification to create exotic foods |
Provided here is a video demonstrating the spherification of foods
Transglutaminase Meat Glue
One of the topics in the field of molecular gastronomy that has generated heated discussion is a material colloquially called, “Meat Glue”. Chemically, meat glues are referred to as transglutaminase. Transglutaminase is an enzyme naturally found in blood which catalyzes the formation of a covalent bond between a free amine group and an acyl group which are found on the ends of proteins. These enzymes aid in the formation of strong protein bonds which do not degrade easily. These enzymes are frequently used to connect different pieces of protein-rich food stuff, mostly meats, together.
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| Schematic of bonding involved in use of transglutaminase |
No US law requires chefs to disclose whether they use meat glues. However, many customers look down upon the practice, worried whether the meat they eat is actually one piece or a mixture of scrap meats. Another concern of critics is that by “gluing” pieces of meat together, the pathogen-covered surfaces of the meat, which are usually seared to kill these pathogens, are left unfettered and pose a health hazard to the consumer. In 2001, the USDA stated that any meat products produced through the use of meat glue must have it clearly marked on the label.
However, chefs defend the use of meat glue, stating that meat glues help reduce waste and allow them to create creative culinary masterpieces, making it possible to design foods with patterns and combine different types of foods together to create never before seen
Transglutaminase, aka meat glue, is sold under its brand name Activa. It is sold as a powder which can directly be applied to the surfaces of the foodstuffs that are being combined. After adding a little water, placing the conglomerate in a vacuum bag, and letting it set in a freezer overnight, the transglutaminase will form bonds. It is sold by the Ajinomoto company, the same company which produces other products such as the commonly utilized neurotoxin food additives, aspartame and MSG (monosodium glutamate). The U.S. Food and Drug Administration lists transglutaminase as “generally recognized as safe.” However, many people are hesitant of eating meat glue because they fear transglutaminase may also possess toxic properties. Transglutaminase is produced by cultivating bacteria using vegetable and plant extracts in the blood plasmas of pigs or cows. However, manufacturers are not required to share the exact method of synthesis, adding to the uncertainty and fear consumers hold regarding this product.
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| Left: Meat-glued chicken and beef. Center: Meat-glued salmon and tuna. Right: Meat-glued lamb and scallops. |
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| Production process of food using transglutaminase meat glue |
Sous-vide Cooking
The last molecular gastronomy technique that will be discussed is sous-vide cooking. So what exactly is sous-vide cooking? This is a technique where food is vacuum packed in a plastic pouch and cooked a closely controlled temperature in a water bath. This allows for a great deal of control and the ability to cook food with extreme consistency. Many recipes can make use of this technique. So why spend the money on such expensive equipment in the first place?
Firstly, sous-vide involves vacuum packing the food product. This allows the carefully controlled temperature, usually around 122 to 149 degrees Fahrenheit to evenly cook the food in polyethylene bags.Polyethylene is a common plastic polymer that is generally regarded as safe for use with food.
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| Polyethylene |
Another benefit of using the bag is that it allows, for example, meat to retain its juices while cooking. Volatile flavors are also saved. Sous-vide also prevents the development of odd flavors from oxidation. Since it is vacuum packed, the amount of oxygen in contact with the food greatly decreases, as does the chance of oxidizing the cooking oil when the oil nears its boiling point. Meat begins to turn to a red color and then to a grayer color when in contact with oxygen as myoglobin is oxidized to oxymyoglobin and then metmyoglobin. Bacteria may also begin to grow. These effects are greatly reduced by vacuum pack-cooking the food, since aerobic bacteria will not proliferate. This can also help reduce the need for adding nitrites, an anti-oxidizing agent
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| Left: Fresh meat which has not been oxidized. Right: Meat that has turned grayer after coming into contact with oxygen. |
Conclusion
By implementing molecular gastronomy in cooking, exciting new kinds of food can be created. Shapes, textures, and even flavors can be generated using a variety of techniques such as spherification, sous-vide cooking, and meat-glue. Although some may stick to more traditional methods, the new wave of approaches to cooking give a contemporary spin on food. Many restaurants and chefs around the country have adopted molecular gastronomy such as Grant Achatz and Wylie Dufresne. Molecular gastronomy truly gives a glimpse into the kitchen of the future.
BCA Chemistry 