Combat-Ready Kitchen, Marcus Karel, and the Military History of Food

It’s little secret that the United States of America has the largest defense budget in the world, outspending the next seven largest national budgets combined.  It’s also well known that few other places on Earth have such prevalent access to the variety and quantity of processed foods as on American soil. What’s less widely known is that these two seemingly disparate facts are actually closely intertwined.

An army marches on its stomach, as the saying goes, and well before we were making strides to land on the moon, or competing for nuclear supremacy, our military was devoting resources to better, faster ways of making, storing, and transporting edible food. We’ve come a long way since the freeze-dried ice cream given out to children’s field trips to planetariums nationwide, and author Anastacia Marx de Salcedo has made an intricate study of how the military has shaped the history of food in America.

In the excerpt below, de Salcedo profiles one scientist whose devotion to studying the intersection of food, water, and deterioration changed the face of food as we know it.

Excerpted from Combat-Ready Kitchen by Anastacia Marx de Salcedo.

Marcus Karel is cut from a fine twentieth-​century cloth that has all but gone the way of the gramophone. Humble, hardworking, and deeply humanitarian, as a teenage member of a semiclandestine Zionist group, he helped Jews escape his home country of Poland after World War II. He then emigrated himself, eventually getting a job as an assistant in the MIT packaging lab and entering their food technology doctoral program. By the late 1950s, he had graduated to studying the permeability of different kinds of plastic films to water and flavor and also discovered his life’s work: understanding how water and oxygen affect chemical reactions in food. Karel successfully defended his thesis in 1960 and was offered a faculty position in the Department of Nutrition, Food Science, and Technology.

Vital to Karel’s work — and food science in general — was the concept of water activity, a new way to understand how its molecules behave in a substance. Water is the major component of almost all food. We living things are full of it — animals, about 70 percent; plants, 80–90 percent — and so, naturally, are edibles. The high proportion of water facilitates a dizzying number of chemical reactions and biological processes. After death, this tissue continues to be highly chemically reactive, although functioning, absent cellular respiration, trickles to a halt (except for enzymatic reactions, which depend only on the presence of their substrates to work). The lack of defenses, both barrier and immunological, turns the nutrient-​rich organic matter into a virtual bacteria and fungi magnet. But although moisture is definitely associated with spoilage, the amount of water in a food doesn’t always predict whether it will go bad.

The conundrum was solved by William James Scott, an Australian bacteriologist at the Council for Scientific and Industrial Research, who, before World War II, had studied spoilage in chilled ox muscle for that country’s beef exporters, and during the war worked to ensure the safety of the food Australia supplied to the Allies. Starting in 1953, he did a series of experiments, adding different amounts of solutes to a nutritious substrate and then, after a set time period, recording the number of organisms for two of mankind’s bacterial baddies, Staphylococcus aureus and Salmonella. The solutes lowered the substrate’s vapor pressure ratio, a standard chemistry measurement. (The vapor pressure of pure water shows how much force water molecules exert on the surrounding air at a given temperature. The vapor pressure of a food at that same temperature is lower, because some of the water molecules are bound to the food material. The vapor pressure ratio, called the water activity, or aw, by food scientists, is the vapor pressure of the food material at a given temperature divided by the vapor pressure of pure water at that same temperature. The more strongly the water molecules are bound to the food material, the lower the water activity.) What Scott found was that there was a vapor pressure ratio below which the population growth of bacteria was virtually zero — 0.85 for S. aureus and 0.90 for Salmonella and most others. (Yeasts and molds can survive down to 0.60.) In early 1957 Scott proposed a new theory, one in which microbial spoilage was related not to absolute water content but to the amount of water available — that is to say, not chemically bound to the food material — for microorganisms to perform vital life functions (ingestion, respiration, reproduction, excretion).

Karel became one of the earliest proponents of Scott’s water activity theory. His Ph.D. student Ted Labuza recalls his final year as an undergraduate in MIT’s Department of Nutrition, Food Science, and Technology: “I had taken a course . . . with him where he introduced the concept of water activity and the application of kinetics to food storage stability. At that time there were no textbooks with this concept. . . . He had just then gotten a grant from the U.S. Army Natick Labs and the air force to work on stability of military and space foods.” Karel’s first space program work enumerated the things that could go awry with deeply dessicated foodstuffs. As it turns out, there were a lot.

First, enzymes, which are present in all animals, most plants, many microorganisms, and fresh products made of the same, weren’t inactivated by freeze-​drying. Unless they were denatured by heat or acidity, these specialized proteins kept on catalyzing chemical reactions, in some cases creating a dark pigment that resulted in unappetizing-​looking edibles. On the other hand, discoloration due to the breakdown and recombination of sugars and amino acids, known as nonenzymatic, or Maillard, browning, was minimal in freeze-​drying. The surprise was lipids, which, when left high and dry, reacted with oxygen, creating a rancid taste.

“The Karel lab was a primary group combining kinetics, water activity, and packaging engineering, and Marcus was the orchestra master,” explains Labuza, who worked on several of Karel’s projects on deteriorative reactions in dehydrated food, “and the players, his ‘science children’ went on in food engineering as faculty somewhere compounding the impact of what Karel taught them.” In 1965 teacher and pupil attended the first-​ever international conference on water activity in food, a life-​changing event for Labuza. “The Natick Center was there; their representative was a guy named Harold Salwin. He’d done a study with cookies that stored them at different relative humidities and what he found was that at lower relative humidities, the shelf life was reduced because of the oxidation of lipids. I was quite interested in that and it became the basis of my Ph.D. thesis.”

The two MIT academics also scored a major funding coup, snagging NASA contracts to continue Karel’s work on flavor degradation in freeze-​dried foods, as well as one “to design foods for the space program under contract to the U.S. Air Force, in a classified research program called Skylab. The idea was to come up with a bar of some sort and study the shelf life of it,” explains Labuza. After that, there was no stopping them. In the course of a few years, in addition to other technical reports for Natick, the air force, and NASA, the duo published articles together on related topics in the Journal of Food Science (1966), Cryobiology (1967), Journal of Agricultural and Food Chemistry (1968), Journal of the American Oil Chemists’ Society (1969, 1971), Food Technology (1970), and Modern Packaging (1971). In 1969 Labuza; Steven Tannenbaum, a colleague; and Karel made the crucial breakthrough that enabled food technologists to put Scott’s 1957 theory to use: a mathematical model that mapped water activity, temperature, and different deteriorative reactions. Water sorption isotherms, which are based on observational data of water activity for each food item under the varying conditions, finally allowed companies to accurately predict shelf life for their products. Says Labuza, “The importance of Natick was that they had the money. The work that they funded really set the basic principles.”

Excerpted from Combat-Ready Kitchen by Anastacia Marx de SalcedoCopyright © 2015. Reproduced by permission of Current, a member of Penguin Publishing Group, a division of Penguin Random House LLC. .