What element, aside from visible sunlight, does the text identify as the primary engine doing the heavy lifting in sun tea infusion?
The *heat* generated by the sun
While the practice is called sun tea, the physical mechanism driving the extraction of desirable flavor compounds is fundamentally thermal. Direct, powerful solar radiation is the engine that generates this necessary heat when the sky is clear. However, when clouds block this radiation, the extraction process stalls because the primary functional component—the heat—is missing. The text explicitly states that the heat, rather than the visual presence of the sun itself, is what coaxes the flavor components out of the tea leaves. Therefore, on a cloudy day, success depends entirely on whether the ambient environment can provide enough sustained heat to mimic the effect that direct solar radiation usually provides.
