A dryer operating under vacuum will require what temperatures?

When a dryer operates under vacuum conditions, it significantly lowers the boiling point of liquids. This is particularly important in the context of food processing and preservation, as it allows moisture to evaporate at lower temperatures. The reduction in pressure leads to a decrease in the temperature needed to achieve the same evaporation rate as would occur at atmospheric pressure.

Using lower temperatures in a vacuum dryer is beneficial for a few reasons. It helps to preserve sensitive nutrients and flavors that might be degraded at higher temperatures. Additionally, it reduces the risk of damaging delicate food structures, which can occur with high-temperature drying processes. This method is especially valuable for heat-sensitive substances, such as certain fruits and vegetables, where maintaining quality is key.

The other options do not accurately portray the required conditions. For instance, "higher temperatures" would be counterproductive since the essence of a vacuum dryer is to minimize thermal degradation. "Consistent" and "variable" temperatures do not align with the specific operational needs of vacuum dryers, which focus on maintaining lower temperatures to facilitate effective drying at reduced pressure.