Gotta wiegh in here. First, as Michael hinted at, there are so many types of ketchup, or catsup out there. In the phillipines, the condiment is made from bananas, there are other fruit ketchups around as well. I've easily made my own ketchup in a pinch by combining canned tomato sauce with corn syrup, cloves, a bit of mace, and allspice. The main flavor componants of comercially made ketchup are tomato, corn syrup, and cloves, with a hint of garlic and onion. After that, you can add what you want. Other good spices inclued ginger, nutmeg, chili powder, powdered mustard. You could add wasabi or horse radish, or cayenne pepper if you so desire.
And to be sure, if you are going to be making home made ketchup from scratch, it will be time intensive and laborious. But then again, so is making your own pickles, your own spaghetti sauce, your own bouliabase, your own demi-glace, your own maple syrup (you try boiling down 40 gallons of maple sap into one gallon. Now that's time and labor intensive work!) etc. You don't make these on a whim. And you don't make them because you just want a quick sauce to put on food. If that's all you want, then go get the pre-made stuff. It's relatively cheap, tastes ok, and is a whole bunch easier.
Making your own sauces from scratch is done for the love of the process, for the love of the challenge, and for the artisan in those who love to cook from scratch. It's not really cheaper to make your own, as you can't get the ingredients in bulk. It certainly eats time like a teenage boy with a hamburger. But the results produce a sense of satisfaction, and often, the results are incomparable with what you can get commercially, or even at a restaurant.
So, if you want to make your own ketchup, by all means, do so. Just know what you're getting into when you start. And if using canned tomato sauce is something you're comfortable with, then by all means, take the shortcut. If not, then I say, use a juicer for those tomatoes. It will still be a lot of work, but less than if using a chinois (that cone-shaped thingy with a wooden pusher).
Seeeeeya; Goodweed of the North
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