Ketchup is easy to create, but you can’t just leave it to simmer without supervision. Fruity bits will stick to the bottom and begin to burn quickly without regular stirring, particularly after you’ve pureed the mixture and returned it to heat to reduce it to the proper consistency. And as the mixture reaches said proper ketchup consistency the simmering bubbles can send hot, sticky missiles of ketchup popping across the stovetop. You don’t want any of this to land on your skin. Furthermore, if you try to hurry this process with high heat you are likely to burn yourself and your ketchup.
For the best ketchup crafting experience use a deep and thick bottomed pot to allow for plenty of room between the top of the ketchup and the top of the pot. Use an oven mitt while stirring and a mesh splatter guard when you’re not. A plate near the stovetop for quick access to your implements—a whisk and a metal spatula—is also handy.
If you’re inexperienced in tending this kind of process, you can also keep a cool water bath near the stove top. If things get too hot, stick the hot pot directly in the water bath. If you sense material stuck to the bottom, do NOT immediately scrape it up. If it’s burned, you’ll mix it into the ketchup and ruin your batch. But often times you can turn the heat off and use your cooling bath. The ketchup in the pot will soften and reabsorb any caramelization stuck to the bottom. Over time you’ll learn to tell the difference between burned and caramelized, but when in doubt pour the contents to another pot to continue the cooking. With careful scraping you can salvage what’s good and what’s not, and be able to continue cooking down the final product.