How Colloids Affect Strength Perception
Solid particles that are smaller than approximately one micron are so small, gravity won’t act upon them while they’re in a solution. As a result, they won’t sink to the bottom of the cup and the beverage will be cloudy in appearance. These undissolved particles in the solution are known as suspended solids or colloids. The amount of colloids, in americanos and long blacks, does a lot to alter taste perceptions. Usually, a high level of colloids in a brew will inhibit the ability to taste, but this can be a positive thing — very small coffee particles coat the palate allowing a higher tolerance to bitterness.
Some instant coffee manufacturers have recently started adding a small portion of extremely finely ground coffee to their products. The ‘microgrinds’ provide this important textural sensation, reduce bitterness, and provide the drinker with an ‘authentic’ texture of traditionally brewed coffee: all of which are sorely missed in most instant coffees.
Air bubbles in espresso crema (also in milk foam) perform a similar role to colloids in coffee. A tiny air bubble, a fat globule, or undissolved coffee particle, will act as a physical barrier between the liquid and your taste buds. This will reduce how intensely the flavour is perceived; the main reason for “milk” destined blends usually being roasted to a darker degree than those intended for black-only consumption, and vice versa. The bitterness of a dark roast is tempered by the fat globules in milk, which inhibit your tongue’s ability to taste it.
Air bubbles inhibiting taste perception