16 November 2011

Why Do Some People Hate Drinking?

This post was prepared in collaboration with Kevin Liu and Naveen Sinha, who describe themselves as - "Two geeks from Harvard and MIT who explore great food from a scientific perspective and blog about it" - Personally I'd describe them as two of the coolest people I've come into contact with, but that might say more about me than about them!

Being scientists they can take a much more detailed look at many of the things we talk about on the blog. Check out there site Why Cook for weekly updates on the latest news from all over the culinary and cocktailian world. Enough chit chat lets get into some knowledge.

I take great pride in asking people what they like to drink and finding something in my home bar that will make them happy. I enjoy alcohol as a lubricant for social experiences and am convinced that in moderation, it has at least some moderate benefits to health. The vast majority of friends I've tested have enjoyed the drinks I've made them. People who swear they can't stand hard liquor or only drink vodka have refilled on swizzles made from anejo tequila.

Except for Tom.

Tom (his real name isn't Tom) cannot stand the taste of alcohol. At all. And I know it's not his fault. He's always a good sport, tasting every single drink I've made for him. Each time, he smiles, as if confident this time, this drink, he'll find something he'll genuinely enjoy and know exactly what to order at bars forever. For me, it's like watching a car wreck in slow motion. I carefully study his face, looking for a sign, the slightest hint of a smile that indicates he's pleased, satisfied, or at least indifferent. But, every time, this venture ends the same. Tom's face tightens with disgust, his eyes squint, his tongue hangs limp from his defeated mouth.

Tom drinks Bud Lime and Coronas. I drink Tom's cocktail leftovers. Once in a while, I'll mix up something exceptionally light and he'll happily accept a glass, knowing he'll never be able to bring himself to ask for an amaretto sour or a dark and stormy (hold the stormy) in a bar. Poor Tom.

I decided to start doing some research. I had to understand why Tom didn't enjoy the same drinks I found so delicious.

Does Alcohol Actually Taste Good? (or are we all just addicts?)

Humans have been drinking alcohol for thousands of years. The earliest evidence we have dates back to the production of alcohol in China around 8000 B.C. And for as long as we've made it, we've treasured it. Pottery fragments left by Neolithic settlements living in modern-day Georgia around 6000 B.C. reveal images of celebration associated with alcoholic beverages.

Of course, early fermented wines and beers were relatively low alcohol. Some societies may have used alcohol production more as a means of preservation than for alcohol's inhibition-reducing effects. In fact, we didn't know how to distill alcohol to stronger strengths until 1200 A.D.

For more on the history of booze, see Drink: a Cultural History

A few thousand years is far too little time to evolve any sort of biological preference for alcohol, but we humans are very good at passing along our taste aversions and preferences through cultural and other unconscious cues. So what if the only reason I think alcohol tastes good is because people enjoy getting drunk and somehow that drug reliance has translated into a taste preference for ethanol? Would cocktails taste better if they were all virgin?

Some of the most telling research I found on the taste of alcohol came from the Department of Otolaryngology (the study of the ear, nose, and throat) at Warsaw Medical University in Poland. In 2000, Dr. Anna Scinska and five of her colleagues performed an experiment that, so far as I can tell, is the most definitive exploration of how people experience the flavor of alcohol available.

Dr. Scinska recruited 20 volunteers to taste small squirts of various concentrations of ethanol, sugar sucrose syrup, citric acid, saline, and quinine, a bittering agent. Perception of ethanol's taste was in question. The other solutions were meant to represent the tastes of sweet, sour, salty, and bitter - the four basic tastes the tongue can experience (MSG is a fifth, but is less explored). The results were intriguing. Every single test subject said that ethanol is bitter, even when it was present only as a 0.3% solution. The second most common taste descriptor, however, was that ethanol tasted sweet.

In the second part of Dr. Scinska's experiment, the test subjects were invited back to compare ethanol to tastes, but this time they were asked to rate the taste similarity of ethanol to a combination of both quinine and sucrose. The results confirmed what had been observed during the first test. When subjects tasted a 10% ethanol solution, they found it tasted most similar to a 3% sucrose solution with just a little quinine (0.005%) mixed in.

From this research, it seemed clear that people find alcohol both bitter and sweet. Everyone appears to find alcohol bitter, but apparently not extremely bitter, regardless of concentration. People also thought alcohol was sweet, but once again, only slightly, regardless of concentration.

These revelations were fortifying for me. The research showed that alcohol delivers a complex mix of bitter and sweet. Even at cocktail concentrations, the flavors were described as "pleasant". In fact, as I did more reading on the subject, I found that other animals (rats, elephants, birds included) seem to seek out naturally occurring alcohol for its sweet taste.

So why did Tom still hate cocktails? Going off the Scinska research, I thought maybe it might have something to do with the way he perceives bitterness. More research was needed.

It's Not Tom's Fault

In 2004, Sarah Lanier, a graduate of the dietetics program at the University of Connecticut, recruited 49 undergraduate students from the UConn population for an experiment. Lanier was working with Dr. Valerie B. Duffy, a professor at UConn who earlier that year had published a paper linking ethanol (the stuff that makes alcohol alcoholic) to a compound called 6-n-propylthiouracil, commonly known as PROP.

Here's how Lanier's experiment played out. Each of the 49 recruits sampled four different drinks: pilsner beer, blended scotch whiskey, instant espresso, and unsweetened grapefruit juice. They rated how bitter or sweet each drink tasted on two scales - intensity and whether they liked the taste. And that was it. The session must have been pretty easy for the college kids. They got free booze, a little coffee, and a few dollars for an hour of work.

But Lanier found some interesting results with this simple experiment. She collected two more important pieces of data about the students: (1) how much alcohol they consumed and (2) whether they were sensitive to PROP bitterness. People who are sensitive to PROP are known as "supertasters" because they find certain foods unbearably bitter. Most people are middle tasters, while some are "nontasters" - people who barely experience PROP bitterness at all. Lanier discovered that nontasters not only found bitter foods to taste less bitter, they also experienced sweet foods as sweeter. On the other end of the spectrum, supertasters found all bitter drinks to taste more bitter.

When Lanier linked people's perception of sweet and bitter to their consumption of alcohol, she discovered something really unexpected. People who thought scotch tasted sweeter and less bitter drank more alcohol on average. In addition, this effect appeared regardless of whether people said they actually liked scotch or not. How the students experienced beer, however, did not seem to have any predictive value on total alcohol consumption. Instead, Lanier found simply that more men tended to say they "liked beer" and those that showed this preference tended to drink more.

The UConn experiment seems to show two things. First, some people experience hard alcohol as extremely bitter and they drink less alcohol of any type as a result, even if they say they like the taste of hard alcohol. Second, although people experience beer very differently as well, they seem much more able to overcome their taste aversion, probably as a result of social pressure.

Aha! Now I understood why Tom could stomach some light beers, but struggled with sweet cocktails. He had probably overcome the bitterness of beer through social pressure and acquired tolerance to aversion, but the whole point of a craft cocktail is to use different strong liquors in harmony. You want to taste the alcohol. But that taste was torture for Tom.

But What About the Burning Taste of Alcohol?

There was one more thing I had to look into before closing the book on the "why do some people hate the taste of alcohol" case. Many of the participants in Dr. Scinska's 2000 study ascribed a sour taste to ethanol, but upon interview, described more of a "burning sensation". The characteristic burn of alcohol is well-documented, but, I wondered, what impact did it have on taste perception?

I posed the question to the question and answer site Quora and after a few months got a well-researched, thorough response from a medical student named Jae Won Joh:

The answer is not simple, unfortunately, and it's actually a bit difficult to pinpoint. Let's go through some of the research I've been able to dig up. Skip the bulletpoints and just go for the intermittent summaries if you're impatient.

· In 1965, Hellekant discovered that cat gustatory fibers respond to ethanol by increasing their firing pattern[1]. These fibers were also responsive to water, acetic acid, quinine, and salt. In cat non-gustatory fibers, ethanol caused a direct increase in firing up to a certain concentration before causing paralysis[2]. This was one of the first studies looking into how ethanol affected taste nerves.

· In 1999, Sako and Yamamoto showed in rats that you could induce aversion to alcohols, suggesting a possible burning/unpleasant sensation[3].

· In 2002, Danilova and Hellekant duplicated Hellekant's 1965 work in rhesus monkeys, showing that ethanol induces increases in firing in about half of lingual non-gustatory receptors. The taste fibers which respond to ethanol are also sensitive light touch and cooling. This suggested some sort of neuronal manipulation by ethanol, possibly with mechanoreceptors.

· In 2002, Trevisani published a brilliant paper showing that ethanol actually potentiates TRPV-1, a heat-gated ion channel that is responsible for the burning sensation elicited by capsaicin. Ethanol potentiated the response of TRPV-1 to capsaicin, protons, and heat; lowering the threshold for heat activation from 42°C to 34°C. This provides a likely mechanistic explanation for the ethanol-induced sensory responses that occur at body temperature.

Layman's summary up till 2002: we thought ethanol was just messing with nerves, but apparently there's this special receptor that it wreaks hell on, and it just so happens to be the receptor for capsaicin, which causes the burning associated with spicy food. Innnnnteresting. Veeeeery interesting...

· In 2004, it was found that ethanol actually activates a neural pathway reactive to sucrose[5]. That's right: ethanol is, at least to a rat brain, not all that far off from sugar. Which, in an evolutionary sense, is not all too surprising, given that they're both energy sources.

· In 2004 and 2005, Lyall showed in a nice series of papers that TRPV-1 is in taste receptors[5], proving that they were definitely in the right location for stimulation. This is basically further confirmation of Trevisani's work, I think.

· In 2005, Simon and Araujo published a nice review of the data thus far[7]. Just thought I'd recognize their paper, it's good.

· In 2009, Blednov and Harris demonstrated that if you knocked out the TRPV-1 receptor in mice, they would show significantly greater consumption of ethanol than their normal counterparts. However, you could still induce aversion in both groups, and withdrawal symptoms weren't different between the two[8].

Layman's summary up till 2009: we know now about alcohol and capsaicin, but it's apparent that alcohol has other taste pathways as well, possibly involving sweetness. It may even involve something else as well, given that you can still get a mouse to hate alcohol even if it doesn't have the capsaicin receptor.

Basically, what Joh summarized was that ethanol seems to trigger a pathway that is also responsible for the burning sensation you get from eating spicy foods and, importantly, that ethanol reduces the temperature at which the pain gets triggered.

I knew from previous research that there is only one way to build up a tolerance to spicy food: eat more spicy food. Perhaps sensitivity to alcohol works in a similar fashion?

How to Deal with Different Types of Drinkers

Everyone knows that flavor preferences vary greatly between people, but I had no idea ethanol could deliver such a complex range of pleasurable and unpleasurable flavors to different tasters. How one experiences alcohol depends on their genetics, social/cultural influences, and tolerance built up over time. Rather than go into all the takeaways, I've organized some advice for dealing with different types of drinkers.

For the beginning drinker

You have to be careful with the beginning drinkers because you have no idea whether they are a supertaster or not. Beginning drinkers are also the most prone to developing preferences for or aversions toward alcohol, so you want to make sure they don't drink too much or have a negative experience - it could deal irreparable damage.

Test the waters - mix something they're familiar with, like lemonade, and add half the alcohol you might add to a full drink. See if they appreciate how the alcohol adds complexity to the drink, or if they immediately pull away, cringing. Then you might have some idea what type of drinker they are and proceed from there.

For the Supertasting Social Drinker

For those individuals who are sensitive to PROP, the only way to make sure they enjoy their drink is to keep the abv relatively low. Highballs, swizzles, shrubs, and the like are classy and can be just as strong as an up drink, but are more diluted. Steps should also be taken to reduce the perceived bitterness of the drink. Avoid bitters and quinine if possible. Instead, emphasize sour and sweet flavors. Consider adding some salt, as salt can reduce the perception of bitterness (see here for an example). Experiment with complex flavors that are not alcohol-based, such as herbs and infused syrups.

For the Connoisseur

For a guest who's a fan of fine scotches or whiskys, you're probably safe to assume either they're not a supertaster or they have acquired a powerful enough preference for alcohol that the bitterness doesn't bother them anymore. Mixing drinks for people like this can be especially difficult because it can be hard to gauge how much tolerance they've developed in their TPRV-1 receptors. If ethanol works anything like capsaicin, what one person sees as a spicy, pleasant sip might appear to another as bland and pale. If at all possible, it might help to have the guest taste a simple blended scotch and describe it. If they find it bland and are looking for a complex drink, it may help to add bitters, quinine, or aperitifs to up the complexity.

For Nontasters

I somewhat suspect I am a nontaster. I love spicy, bitter cocktails and eat kale on a weekly basis (supertasters find many bitter vegetables overwhelming). It's not a bad life, though sometimes I wonder whether I've missed out on taste experiences others with more sensitive taste receptors enjoy. This may be one reason I enjoy smoky cocktails (have you seen our DIY cold smoker?), carbonation, and cocktails with capsaicin mixed or infused in. Nontasters are easy to please, but tough to impress. I've found that simply using higher proof spirits doesn't cut it; the harmony of other ingredients is thrown off. Challenge nontasters with new flavors. I remember once taking a shot of angostura bitters with John Gertsen of Drink. It was one of the strangest things I could imagine doing, but it was delicious. A shot of fernet, anyone?

What type of drinker are you?

1 comment:

Tony Harion said...

Absolutely amazing post.

Thanks for gathering all this info.
Think about how many of your hard drinking friends like spicy food?

Btw, there are a couple of missing links on the “see here for an example” under “For the Supertasting Social Drinker” and “DIY cold smoker”.

I´ve been finding some pretty cool stuff over at why cook lately.
Great work!