Diet Coke
Diet Coke does not use a modified form of the Coca-Cola recipe, but instead an entirely different formula. The controversial New Coke, introduced in 1985, used a version of the Diet Coke recipe that contained high fructose corn syrup and had a slightly different balance of ingredients. In 2004, Coca-Cola introduced Coca-Cola C2, which it claims tastes much closer to Coca-Cola but contains half the carbohydrates. In 2005, the company introduced Coca-Cola Zero (replaced by "Coca-Cola Zero Sugar" in 2017), a sugar-free variation of regular Coca-Cola.
New Coke
In his book "" (2005), Malcolm Gladwell relates his conversations with market researchers in the food industry who put most of the blame for the failure of New Coke on the flawed nature of taste tests. They claim most are subject to systematic biases. Tests such as the Pepsi Challenge were "sip tests", meaning that drinkers were given small samples (less than a can or bottle's worth) to try. Gladwell contends that what people say they like in these tests may not reflect what they actually buy to drink at home over several days. Carol Dollard, who once worked in product development for Pepsi, told Gladwell: "I've seen many times where the sip test will give you one result and the home-use test will give you the exact opposite." For example, although many consumers react positively to the sweeter taste of Pepsi in small volumes, it may become unattractively sweet when drunk in quantity. Coke, on the other hand, may be more attractive for drinking in volume, because it is less sweet. A more comprehensive testing regimen could possibly have revealed this, Gladwell's sources believe.