Ketchup, also known as catsup, is a type of sauce containing spices and a large amount of acid (vinegar or lactic acid), typically tomato-based. Some recipes, particularly those from Australia, may use the ambiguous term tomato sauce to mean tomato ketchup.
Ketchup is commonly used on deep fat fried foods, meat, and eggs. Ketchup is normally applied at the table as a condiment, but it is also commonly used as an ingredient for meatloaf and barbecue sauce.
Interestingly, the original ketchup did not include tomatoes. It was probably a Chinese sauce called "ke-tsiap", based on fermented brined fish or shellfish. The sauce was brought back to Europe by sailors, and appropriated into local recipes. Later, tomatoes were added.
Select good, ripe tomatoes. Scald and strain through a coarse sieve to remove seed and skin. Measure 1 gallon (3.8 litres). When the tomatoes become cold add the remaining ingredients. Let simmer slowly for 3 hours. Pour into hot sterilized 1-pint jars and seal. Process for 15 minutes in boiling water bath. Add 5 minutes processing time for altitudes from 1,001 to 6,000 feet (300 - 1800 metres), and another 5 minutes if over 6,000 feet (1800 metres).