Flavor is a mixture of taste and smell. Your mouth recognizes five tastes: sweet, salty, sour, bitter, and umami (savory). You are probably familiar with the first four: sweet (the taste of sugar), salty (the taste of table salt), sour (the taste of white distilled vinegar), and bitter (the taste of quinine or tonic). Umami tastes like roasted meat, aged cheese, or sautéed mushrooms.
To isolate taste from flavor, hold your nostrils closed when you eat. By eliminating aroma, all you will perceive are the five mouth tastes. In reality, taste and aroma don’t live in isolation, but if you hold your nose when you take a bite of an apple, your mouth will taste sweet sugars, tart acids, and not much else. In fact, without smelling, it’s difficult to tell the difference between fruits with similar textures, like apple and pear, because almost everything that “tastes” distinctive about food isn’t taste at all — it’s aroma.
This is largely because our noses are more sensitive than our tongues. We have about 40 million olfactory neurons picking up odors from the air and from food vapors traveling up to the nose from the back of the mouth. In comparison to the five tastes perceived on the tongue, our perception of aromas is nearly infinite and accounts for the bulk of the sensations we call “flavor.”
Many ingredients, like fruits, herbs, and spices, are loaded with aromatic molecules and have strong aromas even when raw. When these flavorful ingredients are dehydrated, the aromatic molecules concentrate, making them much more powerful for tincturing alcohol.
Aroma chemicals are volatile, which means they are small enough and light enough to float through the air. Taste chemicals are larger and typically water soluble. Aroma chemicals are more similar to oils than to water, and are therefore usually fat soluble. Because of the chemical nature of alcohol, both aroma and taste molecules are partially soluble in alcohol. So when we take a sip of flavored liqueur, we are getting a concentration of flavor, with both taste and aroma molecules roiling across the palate and wafting up the back of the throat to the olfactory receptors in the nose.
Depending on the concentration of flavor molecules in an ingredient and the percentage of alcohol in the liquor being tinctured, developing a full-flavored liqueur can take anywhere from a few hours (using crushed peppercorns or grated horseradish) to several weeks (with chopped celery or pear).