Bitterness, Pt. II

Phew! Where’s the time gone?

Anyway, let’s get on with it. I’ve already discussed the primary source of bitterness in beer, so now I’ll revisit the topic of bitterness from a different view: the physiology of bitterness.

The sensation of bitterness is not well understood at all. Nearly every aspect of bitterness is shrouded in complexity, and although new research is continually expanding our level of understanding there is still a great deal to be learned. The reasons bitterness is a tricky subject to elucidate are numerous and varied. There are a wide variety of chemical compounds which are bitter, such as polyphenols, organic acids, peptides, salts, sulfimides, and acyl sugars. This variety in molecular size and shape in turn implies a variety of mechanisms of operation. There is also a huge variation in how bitterness is perceived by individuals, and these variations are largely genetic in origin. Further confounding our understanding of these mechanisms are the difficulties that arise when attempting to communicate the qualities of bitter sensations. There are no agreed upon vocabularies for describing bitterness and its qualities, so while one person may describe caffeine as having a harsh and unpleasant bitterness another person may call it medicinal and lingering. Are they perceiving the same sensation, and is there even a way to tell for sure? Yet another factor in the complexity of bitter taste is the interactions that bitter sensations have with other sensations, most notably sweetness. Certain mixtures of bitter and sweet compounds can have interesting and unexpected effects on each other, with some sensations being suppressed by the presence of other compounds. In some cases there can be a synergistic effect where the total sensation is greater than what would be expected from a merely additive effect. In this article I will explain some of the mechanisms and characteristics of bitterness as we understand it so far.

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Beer and our 5 senses

So, now that I’ve briefly introduced bitterness, I suppose I should step back and start with a more basic subject: how you use your 5 senses and the 5 basic tastes to enjoy beer.

The 5 Senses:

We all remember from grade school that the human body’s five senses are sight, sound, touch, smell, and taste. It’s fairly obvious that smell and taste play a part in experiencing beer, but what about the others?

Our eyesight comes from light in the visible range of the spectrum striking our retinas and exciting molecules which transmit a signal for our brain to interpret.  In beer, we notice the color, the clarity, the foam thickness, and the lacing in the glass.  All of these things are very important in building our impression of the beer.  It’s amazing how the color of the beer can bias the drinker before they’ve even tasted it.  I’ve seen taste panels ascribe caramel-like flavor descriptors to pale American lagers with caramel food coloring added to mask the true color.

Bitterness

It’s understandable why bitterness is an acquired taste. Despite what surely must pain “iso-philes” (bitter beer lovers), the old “bitter beer face” commercials have some truth to them. It’s generally agreed that bitterness has been an evolutionary signal for a possible poison, so it’s no surprise if we are initially put off the taste of bitterness.

What’s not quite so understandable is how the sensation of bitterness differs for each of us. Much of the research I’ve been involved with has shown that various bitter compounds elicit different responses from each person, with few correlations able to be drawn. Each compound has different intensities and often different qualities as well, including harsh, medicinal, vegetative, lingering, etc.

The predominant source of bitterness in beer are the iso-alpha acids. These are derived from the alpha acids which are present in the flowers of the female hop plant, Humulus lupulus. These alpha acids are found in the lupulin glands of the flower, which look like tiny yellow pollen-like balls clustered together. Much of the other material in the hops which brewers value (such as aroma compounds) are also contained in the lupulin glands, but today we discuss the alpha acids.