Lemon

Lemon is a citrus fruit used as juice, zest, and peel. Its serious kitchen jobs are acid and, in marmalade, peel.

Ohio State groups lemons with fruits that, if not overripe, have enough natural pectin and acid to gel with added sugar only ¹. That is a jelly-and-jam chart, not a license to invent a canned lemon product. When a spread recipe calls for added acid, it specifies lemon juice or Citric acid because acid is required for gel formation, not as perfume ¹. Commercial pectins themselves are made from apples or citrus fruit.

Jam and jelly. Pectin, Sugar, and Acidity are the contract. Lemon juice is the acid bottle most kitchens already own. See Jam.

Marmalade. Ohio State: marmalades are soft fruit jellies with small pieces of fruit or peel; they often contain citrus ¹. The peel is structure and bitterness, not garnish. Details: Marmalade.

What to notice. Juice should taste sharply sour, not flat or dish-soapy. Peel oil is the aroma; pith is bitterness and pectin. Lime is a sibling citrus, not an automatic swap in a tested canning acidification.

Tomato-canning lemon-juice amounts belong to the tested process for the tomatoes and jar.