With 1 being the best and 4 being the worst, their average score for the new soda was 2.0. The aspartame contained in diet soda stored over time can break down into formaldehyde and DKP, two very dangerous poisons. Taste tests revealed a noticeable difference among tasters. The higher the heat of storage, the worse the taste. Diet soda stored for ten weeks loses flavor.
Temperature creates two effects.
First, the higher the temperature of storage, the higher the level of DKP in the soda. Second, room temperature seems to create the highest levels of formaldehyde in soda. At very high temperatures, the formaldehyde breaks down. However, even stored in a refrigerator at cold temperature, the aspartame breaks down into formaldehyde. After diet soda containing aspartame is purchased it should not be stored in the heat or under any condition for a long period of time.