For all types of pasta, protein is the most important factor in determining texture. More protein is generally better than less, but all of our spaghetti contained between 4 and 6 grams per serving, and those numbers didn't correlate with our rankings. However, gluten-free pastas don't behave in exactly the same ways as pastas made with white or whole-wheat flour. Most get their strength from rice flour—in fact, it's a primary ingredient in every brand we tasted—and it's much lower in protein than either white or whole-wheat flour. Although particles of fiber can interfere with the protein bonds in wheat pasta and cause it to weaken during cooking, rice fiber plays a helpful role in gluten-free pasta—to a point. The ideal combination turns out to be a relatively high amount of protein (at least 4 grams) and a fiber content that's less than half that amount. Our two favorite brands have a relatively high amount of protein that is at least double their amount of fiber; both remained intact but tender after cooking, earning praise for their ability to pass as “regular” pasta. The rest of the samples, all of which had been soft and mushy or gritty and grainy, had a near-equal ratio of protein and fiber.