"Flavor" by Bob Holmes

"We are the only species that seasons its food,
deliberately altering it with the highly flavored
plant parts we call herbs and spices." (p. 4)

"The notion that you can somehow “taste the soil” in a wine is completely false. Grape vines take up only water and simple nutrients like nitrogen, potassium, and calcium from the soil. They make all their more complex biomolecules— including the flavor volatiles— in-house. To put it more bluntly, none of the volatile molecules that determine a wine’s flavor come directly from the soil. ... Instead, a vineyard’s soil affects flavor indirectly, by altering how the vine grows and, especially, how quickly the grapes ripen." -- Bob Holmes. Flavor: The Science of Our Most Neglected Sense (p. 216- 217). 

Flavor and how it's perceived: two fascinating concepts. Recently, neuroscientists and other researchers have been making remarkable progress in understanding our sensory perception of the volatile molecules in food and drink -- the elements that make flavors vary. Tomatoes, ripe strawberries, fake strawberry flavor, wine grapes, bitter vegetables, seared steaks, artificial chicken stock, and other foods are the subjects of Canadian journalist Bob Holmes' reporting.

As illustrated in the quote above, Holmes explores some of the myths about what we taste and how these tastes get into our food. I choose his discussion of wine -- only a small part of his book -- to illustrate how many revealing details he presents. His explanation of the actual role that soil quality plays in creating wine-grape flavor is something I've been hoping to learn for a long time. The same clone of a particular type of grapes does indeed yield wines of varied flavors -- the vines experience different degrees of stress which affect their sugar content and their flavor elements (mainly volatile chemicals).

The way the grapes are handled during and after the harvest is another surprising source of variation. Here's another quote that shows how this works:

"If you pluck a grape off the vine and chew it, you won’t notice much passion fruit flavor, because the thiol molecules haven’t formed yet— only their odorless precursors are present. The thiols themselves form during fermentation, as the yeast attack the precursors and split off thiol molecules. Rough handling of the grapes causes them to accumulate more of the precursors, so machine-harvested grapes yield wines with about ten times as much thiol as handpicked ones. This, incidentally, may be part of the reason that New Zealand sauvignon blanc, which is generally mechanically harvested, tends to have a much more pronounced passion fruit flavor than French sauvignon blanc, which is usually hand harvested. Even trucking the grapes from vineyard to winery leads to more thiols in the finished wine." (pp. 217-218). 

And finally, he writes about fermentation: "different yeasts can yield very different wines from the same juice. Winemakers are very aware of this, and put a great deal of thought into their choice of yeast." (p. 218).

Through most of the book, Holmes explains how human sensory apparatus enables people's widely varying response to foods. He shows not only the role of our taste buds and our olfactory system, but also other perceptions of food like how we hear it crunch and how it appears on a plate, and how the stinging and burning of chilies is perceived with our heat-and-touch sensors. He reports on a variety of studies that highlight the role of the context where we eat in how we respond to tastes -- even ambient lighting and noise.

The role of genes that control perception of volatile chemicals (the natural or artificial substances that account for varied flavors) seems to be a critical part of how human variation occurs. Genetics of taste is a study that's in its early stages and in some ways offers more confusion than clarity about how individual responses differ, according to Holmes' account of current research. "Clearly," writes Holmes, "the link among genes, taste perceptions, and actual food choices is not a simple one." (p. 41).

The difficulty neuroscientists encounter in analyzing the genetic component of taste arises for at least two reasons. One is that each person's experience with foods, especially in childhood, creates individual reactions to the various chemicals, so two individuals, despite having the same genes, can react differently anyway. Even so-called super-tasters don't all have the same response to the tastes they perceive. Further, the working of the taste buds and olfactory receptors differ for various taste elements in foods. For example, receptors for the so-called fifth taste, umami, are different from those for salt or bitter taste: "Our umami receptors max out at low intensity, so we’re physically unable to experience very umami in the same way we can taste very salty or very bitter simply by piling on the salt or brewing a cup of extra-strong espresso." (p. 25).

Holmes interviewed a very wide variety of experts including neuroscientists, agronomists, flavor scientists in commercial labs, and wine growers, among others. I have read several other books on the general topic of how humans perceive flavor and taste, including several books that were written by his interview subjects, or books that interviewed the same sources. As a result, I found some of the chapters a bit boring as I had read the same material before, often in much the same form. But on the whole it's a really great book, and its updates on the current state of science and technology of food, challenges to chefs who want to apply this science, and overall understanding of flavor and taste are wonderful!