What characteristic is associated with middle notes in essential oils?

Middle notes, often referred to as heart notes, are known for their moderate evaporation rate. This characteristic allows them to emerge once the top notes of an essential oil blend have dissipated. Middle notes typically set the foundation for the blend and tend to have a balanced aroma profile that harmonizes with both the top and base notes. They play a crucial role in a blend's overall scent and are often responsible for the core fragrance.

In terms of their function within aromatherapy, middle notes usually provide emotional balance and help to smooth the transition from the lightness of the top notes to the deeper, more persistent base notes. This makes them essential for creating well-rounded and cohesive blends.

The other characteristics listed in the options do not accurately describe middle notes. For instance, while heavier aromas may be associated with base notes, middle notes usually possess a lighter, yet rich scent. Their duration in the body typically exceeds the shorter time frames suggested for other types of notes, as they are designed to linger longer than the fleeting top notes.