Sylvia asked: “What is the difference between stock and broth?”
It’s fine if you use the terms interchangeably. Many professionals do. And even cooks who insist on a distinction might have a hard time deciding, in practice, which is the appropriate term for any given cupful.
Both liquids are produced via the same basic process: simmering meat and/or vegetables in water. Typically you start with aromatic vegetables such as onions, celery, and carrots. Sautéing them first gives the cell walls a high-heat head start at breaking down, and the oil added at that stage allows fat-soluble flavor compounds to come out of the produce and into the fat..
Then, during a lengthy simmer in water, the plant cells break down more fully, giving up their sweet, salty, savory contents. Droplets of oil containing the dissolved fat-soluble aromatic compounds are distributed throughout the liquid.
If there’s meat and/or bones in the pot, they also release their savory amino acids, salts, and other flavorful components—but also collagen, the firm three-stranded structural protein that abounds in animal tissue. With long cooking, the collagen’s triple strands unravel into single strands of gelatin, which dissolves into the water and gives it that luscious delicate viscosity that makes it satisfying to sip, and also work as a sturdy building block for soups and sauces.
Right there we have begun to sneak up on the answer to the question. The difference between stock and broth is not in their components or how they’re made, or even in what they are. The difference is in how they’re used.
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Stock is an ingredient. The flavorful, full-bodied fluid provides the backbone for innumerable recipes, whether used by the quart as a cooking liquid or reduced to a potent concentrate and added to dishes by the spoonful.
Broth is a food rather than an ingredient: You can enjoy a cup or bowl of it as is, or with add-ins like matzo balls. Stock can be turned into broth with just a bit of seasoning, or you can just drink it and call it broth.
Very confusingly, the products in the supermarket that are used as stock—used to cook with—are most commonly labeled “broth,” although they’re sometimes labeled “stock”.
Products labeled “bone broth” are generally significantly higher in gelatin than ones without the word “bone,”but otherwise not very different: They can be used as stock or eaten as broth.