Caramel, maple, cotton candy, strawberry. These compounds smell sweet without being sugars. They trick your brain through your nose. And ethyl maltol is your primary tool here.
Furanones are oxygen-containing ring compounds that smell sweet. Not taste sweet. Smell sweet. Your tongue doesn't have receptors for furanones. Your sweet taste receptors (T1R2/T1R3) respond to sugars, artificial sweeteners like sucralose, and certain amino acids. They do not respond to ethyl maltol or furaneol. But your nose detects these compounds and sends the signal "sweet" to your brain, which integrates it with whatever your tongue is reporting.
This is one of the most powerful tools in flavor formulation: the ability to increase perceived sweetness without adding sugar, calories, or actual sweetener. When you add ethyl maltol to a formula that already has some sucralose, the ethyl maltol amplifies the perception of sweetness through a completely different pathway. The tongue says "a little sweet." The nose says "this smells very sweet." The brain averages them and you perceive "sweet." That's the retronasal trick.
Furanones tend to be moderately volatile. They're mid-note to base-note compounds. They don't fire fast like terpenes. They build over the sip and linger in the finish, which is why their sweetness feels "warm" and "lingering" rather than "bright" and "immediate" like actual sugar.
What you need: Ethyl maltol, PG, two tasting cups, plain water, sucralose solution (or simple syrup).
Cup A alone demonstrates olfactory sweetness with zero gustatory sweetness. The tongue says "water." The nose says "sweet." Cup B is pure tongue sweetness. The combination is what great formulation sounds like: layered sweetness from two different sensory systems, creating a perception that's more than the sum of its parts.