Tomato Broth
2 cups canned tomato 1 cup water 1/2 tablespoon Karo, Blue Label 1 teaspoon salt 1/8 teaspoon pepper Few drops onion juice 1/8 teaspoon baking soda 1/4 teaspoon celery salt 1 pint milk 1½ tablespoons Argo or Kingsford's Cornstarch 1/2 tablespoon Mazola Stew the tomatoes, seasonings and Karo ten minutes. Strain, but do not rub all the pulp through. Add the baking soda do not rub all the pulp through. Add the baking soda and thicken with the cornstarch creamed with the Mazola.
A cream of tomato soup from a corn-products promotional booklet, which is why every third ingredient is a brand name. The printed method has a typesetting stutter and never tells you what to do with the milk, so the sequence needs reconstructing.
- The missing stepThe milk appears in the ingredient list but not the method. Scald the pint of milk separately, then combine it with the thickened tomato base off the heat — pouring the tomato into the milk rather than the reverse reduces curdling further.
- Why the sodaThe 1/8 teaspoon of baking soda neutralises enough tomato acid to keep the milk proteins from clotting. Add it to the strained tomato, expect it to foam, and do not increase the amount: excess soda flattens the tomato flavour and leaves a soapy edge.
- Brand names decodedKaro Blue Label was the light corn syrup of the day; half a tablespoon is there to round off acidity and any mild honey or sugar does the same. Argo and Kingsford's are plain cornstarch, and Mazola is corn oil — butter works and tastes better here.
- Onion juiceGrate a peeled onion on the fine side of a box grater and use the liquid that collects, a few drops only. Grated onion pulp or powder will cloud a broth meant to stay smooth.
- Canned tomato then and nowTwo cups of 1910s canned tomato meant whole packed tomatoes in their own thin juice, not concentrated purée. Use canned whole or crushed tomatoes with their liquid; if you substitute passata, thin it, or the soup comes out heavy.
- StrainingThe instruction not to rub all the pulp through is deliberate — it leaves the seeds and coarse fibre behind while keeping enough body that the cornstarch has something to cling to. A food mill or a coarse sieve and a light hand does it.
- ThickeningCream the 1 1/2 tablespoons cornstarch with the oil, slacken with a little of the hot tomato, then stir it back in and cook two to three minutes at a bare simmer so the starch loses its raw taste. Cornstarch thins if held at a hard boil or reheated repeatedly, so serve it promptly.
- YieldAbout 4 1/2 cups after simmering and straining, or four first-course servings.
This reads like an advertisement because it is one: Karo, Argo, Kingsford's and Mazola were all products of the Corn Products Refining Company, and booklets of this kind were issued in the early twentieth century to show home cooks that corn syrup, corn starch and corn oil belonged in everyday cooking rather than only in candy and laundry. Cream of tomato soup was the ideal vehicle, since it needed a starch thickener, a touch of sweetening against the acid, and a fat to cream the starch into — three company products in one bowl. The baking-soda trick for keeping milk from curdling in tomato soup was in circulation in American cookbooks by the 1890s and appears in Fannie Farmer and her contemporaries; the corn oil in place of butter is the newer note, since Mazola was introduced only in the 1910s.