Why does the sun tea method present a food safety risk regarding bacteria multiplication?
The water temperature can easily hover in the $40^ ext{o} ext{F}$ to $140^ ext{o} ext{F}$ zone for extended periods, allowing pathogens to multiply without being killed by boiling.
The primary food safety concern stems from the interaction between the slow warming process of sun tea and the bacterial temperature danger zone defined by the USDA ($40^ ext{o} ext{F}$ to $140^ ext{o} ext{F}$). If bacteria are introduced via ingredients or containers, the initial phase of sun steeping involves the water temperature sitting in this zone for a prolonged time while it gradually heats up. Furthermore, since the water is never brought to a boil ($212^ ext{o} ext{F}$), the lethal temperature required to kill existing pathogens is never reached. This combination—the multiplication of bacteria within the danger zone combined with the lack of a kill step—creates a significant risk that food safety experts cite when cautioning against this method.
