Spit and image: How saliva customizes your wine tasting experience

Wine has the potential to be much more flavorful than it ever is coming out of the bottle. How much of that flavor blossoms on your palate is up to you. We all have differences in our taste buds, smelling sensitivity, allergies or smoking habits, memories and vocabularies related to how we turn molecules in our mouths into sensations and thoughts and words. But the differences begin earlier than that. We are, in fact, working with personalized sets of molecules from the moment wine hits mouth. I know: this sounds like the half-baked promise of some convincingly Rag and Bone-clad entrepreneur trying to sell you some new wine app. It’s not. It’s chemistry, with some help from the highly personalized cavalcade of bacteria inhabiting your oral cavity.

Wine contains far more potentially aroma-inducing molecules than you ever actually perceive. Don’t take it personally; it’s the wine, not you. To be smelled, molecules must be able to leave the “liquid phase” in your wine glass or your mouth to enter the potentially sniffable air. Molecules can’t enter the air when they’re bound to large, heavy, decidedly un-aerodynamic sugar molecules (present even in dry wines, in small but significant amounts). Conveniently, enzymes in your saliva are designed expressly for the purpose of breaking bonds with sugar molecules. This isn’t a special ability developed by wine-drinking peoples adapting for maximum enjoyment. Digestion begins in the mouth – those sugar-active enzymes are only one of several kinds of salivary enzymes – and if you chew a bite of bread or potato long enough, it will begin to taste sweet as your saliva breaks the starch down into simple sugars. On contact, your saliva begins liberating wine aromas into the air inside your mouth and the back of your throat (the pharynx) where they can travel up to your nose (the “retropharyngeal” path) and be smelled.

Malolactic bacteria produce enzymes called glycosidases that free up aroma compounds bound to sugars in wine.  Left, bound aroma compounds without glycosidase treatment are not volatile, so they can't be smelled.  Right, glycosidases liberate aroma compounds into the headspace.
Enzymes called glycosidases free up aroma compounds bound to sugars in wine.

Saliva wreaks other changes on wine molecules, too, thanks to other enzymes and proteins. The quick shift from wine’s strongly acidic pH – usually pH 3-4, somewhere between cola and orange juice – to your saliva’s fairly neutral one also changes the chemical form of some molecules, sometimes changing them from aromatic to un-aromatic versions or vice-versa. All of this explains why a wine’s flavor seems different in the afterglow of swallowing compared with when you take that initial exploratory sniff. It isn’t just the addition of the basic information your tongue can contribute about sweet, salty, sour, bitter, and umami. You’re actually creating new aromas as you sip, swish, and swallow.

Everyone has saliva (unless you have Sjogren’s syndrome but, statistically, less than 3% of you do, and even then you’ll usually just have less saliva). But not everyone has the same saliva. First, those enzymes aren’t identical for all of us. A recent study measured the effect of saliva from normal-weight versus clinically obese folk on white wine aroma. The “obese” saliva liberated fewer aroma molecules compared with its “normal” counterpart. Several categories of compounds that contribute to fruity aromas (esters and acetates) were released in quantities reduced by 40 to 60%. That’s a lot. The story goes that we want to eat more of something when it’s less satisfying (cue the argument in favor of a little really good cheese over a mound of the processed stuff). It may be that overweight people tend to want to consume more because they’re enjoying less. It’s worth noting that wine isn’t a major contributor to people being overweight, and this theory applies a lot more to food portions than to drinking too much. The real moral of the story is that not seeing eye to eye on a wine’s flavor isn’t just about different taste buds and neural connections and memory triggers. It’s partially a matter of body chemistry.

Now, a major problem with these sorts of studies is that they rely on made-up categories. People don’t come in “normal” or “obese;” weight and health are a continuum. By lumping together all of the small people and all of the big people, we’re seeing one great big average instead of depicting what’s actually going on in anyone’s mouth. Also, the “obese” saliva samples used for research tend to come from severely obese people, as in folks waiting for their number to come up for bariatric surgery for weight reduction; precisely what, if anything, those samples say about your average pudgy fellow is up for grabs. We can say that different people have different saliva, maybe with some differences associated with weight, or associated with some other factor associated with weight, and that’s about it. I’ll put away my soapbox now.

Besides, these differences aren’t just about how much you weigh, thanks in part to microbiology. Salivary enzymes have help from your oral microbes, which are in fact so unique to you that individual humans can be fingerprinted by the combination of bacteria they host. Those bacteria make enzymes – different ones, depending on the bacteria – and so they, too, contribute to a change in what goes into our mouths versus what goes down our throats or up that retropharyngeal path to our noses. Studies are beginning to ask: what difference does all of that oral microbiology make to the way we taste? And again, one of those studies asked: what difference do they make to the way we taste white wine?

Tongue-sourApplying bacteria from three different (all “normal-weight” this time) human mouths to “odorless grape glycosides” – those scentless sugar-bound molecules I mentioned earlier – some liberated dramatically more aromatic molecules than others. The wine should give one of the three tasters an extra hit of linalool, a pleasantly floral and spicy compound, for example, because his or her bacteria were able to enzymatically release more of it. Explanation for why your partner calls the pinot gris rose-scented and proclaims it lovely while you think it’s a little blah and one-note? That’s more than we can say at this point. Still, there are things going on in your mouth that change the way your wine tastes, and they’re not the same for everyone.

Your oral microbiota are influenced by a lot of factors: hygiene, sure, but also the microbiota your parents had, whether you smoke, your eating habits, where you’re from, drugs you take, maybe your weight, and your genes, among other things. The good news is that, weight-related differences aside, no one’s trying to tell you that your mouth bacteria are good, bad, or in need of an upgrade if you want to be a good wine taster. It’s true that playing host to some batches of bacteria can be better than others in some settings. Maybe you’ve heard about fecal transplants, where fecal bacteria from a healthy person are introduced into someone with a disorder like irritable bowel syndrome or whose normal bacteria have been wiped out by antibiotics? Well, we’re not doing that for mouths yet.

I’m glad; the wine world gives us too many reasons to feel inferior already, and we don’t need another excuse for judging each other. Think of this as one more way to help explain why you and your tasting buddy can sometimes come to such different conclusions about the same wine. For casual tasters, it’s a curiosity. For researchers studying the science of wine flavor, it’s one more way to help explain why humans are so inconsistent about describing what they put into their mouths. And, eventually, for wine competitions, maybe it will mean screening potential judges on the basis of a saliva sample. But first we’d have to agree on what a “normal” mouth looked like, and if history tells us anything about getting wine tasters to agree, I’d say no one has to worry about that new flavor of discrimination any time soon.