Ketchup

Ketchup, also spelled catsup, is a popular table condiment known for its sweet and sour flavor profile.

While most people today associate the term with tomato-based sauce, its history includes many different varieties. Early recipes utilized ingredients like mushrooms, oysters, mussels, egg whites, grapes, or walnuts. Today, tomato ketchup is the dominant form, made primarily from tomatoes, sugar, and vinegar. It is often seasoned with spices such as onion, allspice, coriander, cloves, cumin, garlic, or mustard. Some recipes also incorporate celery, cinnamon, or ginger to add complexity. This versatile condiment is frequently served with hot, fried, or greasy foods. It also serves as a base for other dressings, like Thousand Island or Marie Rose sauce.

The production of modern tomato ketchup relies on a specific balance of ingredients and chemistry.

Manufacturers combine tomato solids with sugar and vinegar to achieve a stable, flavorful product. Spices are added to create distinct flavor profiles. The thickness of the sauce is influenced by pectin, a polysaccharide found naturally in tomatoes. Pectin helps create a gel-like matrix that holds the ingredients together. In the United States, the USDA even grades ketchup based on its density, known as specific gravity. "Fancy" ketchup has a higher concentration of tomato solids at 33% and a specific gravity of 1.15. Other grades, like "Standard," have lower concentrations of 25% solids and a specific gravity of 1.11.

Ketchup is scientifically classified as a non-Newtonian fluid, specifically a shear-thinning or pseudoplastic fluid.

This means its viscosity, or thickness, changes when it is subjected to stress. When you shake a bottle or squeeze it, the molecules within the suspension respond to the shear stress. The small polysaccharides, sugars, and acids align themselves to move more easily through the matrix. This alignment causes the viscosity to decrease, allowing the sauce to flow quickly. Once the stress is removed, the molecules return to a disorganized state and the sauce thickens again.

This unique property is why ketchup often requires a shake to get it moving out of a bottle.

The history of ketchup is a journey of changing ingredients and global influences. The term first appeared in English in 1682, appearing in print as ketchup or catchup. Some researchers believe the word has roots in the Amoy region of China, possibly meaning "tomato sauce" or referring to the brine of pickled seafood. Another theory suggests it comes from the Malay word for soy sauce. There is also a European-Arabic theory linking it to the French term "food in sauce" or the Arabic word for pickling with vinegar. In the United Kingdom, mushroom ketchup was a primary variety during the 1600s. In the United States, mushroom ketchup was prepared by British colonists as early as 1770.

Tomato ketchup specifically began to emerge in the 19th century through various recipes and innovations. James Mease published the first known tomato ketchup recipe in 1812. In 1824, Mary Randolph included a tomato ketchup recipe in her influential cookbook, "The Virginia Housewife." Jonas Yerkes is credited as the first American to sell the condiment in a bottle, eventually distributing it nationally by 1837. As industrial production grew, manufacturers increased sugar content to improve preservation. This shift helped create the sweet and sour profile common today. In Australia, tomato sauce remained more sour and runny compared to the sweeter, thicker American version.

Modern ketchup was shaped significantly by early 20th-century food safety regulations.

In 1906, the Pure Food and Drug Act was passed in the United States. This led to a debate over using sodium benzoate as a preservative. Harvey W. Wiley, the "father" of the FDA, challenged the safety of benzoate. In response, entrepreneurs like Henry J. Heinz sought alternative recipes. In 1909, bacteriologist Katherine Bitting proved that increasing sugar and vinegar could prevent spoilage without artificial preservatives. By using ripe tomatoes, which contain more pectin, companies could also create a thicker product without needing benzoate. These scientific advancements helped establish tomato ketchup as a dominant condiment.

Beyond its role as a simple dip, ketchup is integrated into various culinary systems and modern technologies. It is used as a flavoring additive in snacks like potato chips. In fast-food settings, it is often served in small sachets, tubs, or even dispensed from hand-operated pumps.

Researchers continue to study the physics of ketchup to improve the dining experience. In 2017, MIT researchers developed a bottle coating to help the product slip out without residue. In 2022, researchers at the University of Oxford found that squeezing more slowly and using a wider nozzle can prevent splatter. Even the tendency for water to separate and form a layer on top, known as leaching, is a subject of molecular study. This occurs because of the instability between hydrophobic and charged molecules in the suspension.