How on earth are we supposed to use “glasses” to control alcohol intake?

I have written recently about wine intake and the effect of the alcohol on us (eg. last week’s post: The effect of red wine is different from white). One aspect of this topic has been recommendations for the maximum alcohol intake per day or week, for any given adult person. This intake is often expressed in “standard glasses” (eg. one glass per day on average). This is meant solely to be an approximation to actual intake, of course. As a guide, 1 Standard Drink is usually taken as being roughly equal to 12 ounces (350 ml) of beer, 5 ounces (150 ml) of table wine, and 1.5 ounces (45 ml) of 80-proof liquor.

There are three possible issues with using this approximation, in practice, for wine drinkers. The first is the variation in alcohol content of the wines of the world, which can vary from c.8% to c.16% (ABV). * Clearly, the latter wines involve the consumption of twice as much as alcohol as do the first ones, if we go by number of glasses. It is assumed, I guess, that in practice a standard glass has a standard percent alcohol, say 11—13% (Here's how much alcohol is in wine, from lowest to highest).

This issue has been discussed by the general media (Alcohol levels can make a big difference). In particular, it has been noted that we all differ in the rate at which our liver breaks down the alcohol we have consumed, and that this is also more problematic for females, on average — this means that the actual amount of alcohol does, indeed, matter.

The second possible issue is the size of the glasses that you are using. For example, it is easy to mis-judge the amount of fluid in larger glasses compared to smaller ones. The third possible issue is the shape of the glasses. That is, it is easy to mis-judge the amount of fluid in glasses of some shapes compared to others.

I have written about wine glasses a couple of times before:

• What do wine glasses and hamburgers have in common?
• How do so-called alternative wine packagings compare?

However, this is worth re-visiting, given the current state of discussions about health and wine.

So, let’s take a look at some wine glasses. Here is a selection for you. As suggested by the figure legend, these glasses are different in both size and shape, but they all contain the same amount of red wine. Does it look like it to you?

Clearly, half-filling most of these glasses would drastically mis-estimate the amount of wine contained. In particular, glasses often hold more fluid than we think. It is commonly reported that drinkers under-estimate the amount of alcohol they consume, thinking that a standard drink is of greater volume than it actually is, which is called the “over-sizing effect”.

We do, of course, need personally to take into account the shape and size of the serving vessel, when we try to judge the amount of wine being consumed (as shown above). This is not a trivial suggestion. For example, an experiment in 21 pubs, bars and restaurants in England (Impact on wine sales of removing the largest serving size by the glass. PLOS Medicine 21(1): e1004313) has reported that:

Removing the largest serving size of wine by the glass from those available reduced the volume of wine sold. This promising intervention for decreasing alcohol consumption across populations merits consideration as part of alcohol licensing regulations.

In other words, we really do mis-judge our own wine consumption when we try to base it on the number of glasses that we have consumed. In particular, it is reported that: Risky drinkers underestimate their own alcohol consumption. (Note that, in the extreme, the Riedel “Sommelier” Burgundy glass is famous for holding a full 750 ml bottle!)

This topic has also been discussed in the general media (The accidental binge drinker: how much we really pour). It has been suggested that drinkers should actually count each glass as being two servings, not one, when drinking out. At home, you can keep track of the bottle contents, not the number of glasses (although, in contradiction, see: Extra-large wine bottles are having their big moment). Just to confuse things, U.S. restaurants can vary a lot in how much they give you (You're not crazy, wine pours at restaurants are shrinking).

Other online reports are listed at The Stealth Syndromes Project: Sources, under-reporting of alcohol consumption.

We also need to behave responsibly, of course, since alcohol does not mix well with many human activities, driving being the most obvious one. In my lifetime, I have been subject to the following restrictions on my blood alcohol content (BAC) while (allegedly) in control of a motorized vehicle:

• 0.08 (back when I was a teenager in Australia)
• 0.05 (currently in Australia — government slogan: “Under oh-5 or under arrest”)
• 0.02 (currently in Sweden).

For a person of my weight, these roughly correspond to 3, 2 and 1 Standard Drinks, respectively. Now all I have to do is get my estimation technique right!

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* Less than this is Low Alcohol Wine, and greater than this is Fortified Wine.