How many drinks are there in a bottle of wine?

How much wine you drink on any given occasion is a serious issue, not just for your own health, but for the happiness of those around you. Even more seriously, the most dangerous place you can be after a drink or two is behind the wheel of a car — there is a borderline between fun and danger.

For this decision to be practical, you need to be able to estimate how much you have consumed, at least roughly. We have been told that drinkers commonly under-estimate the amount of alcohol they imbibe, thinking that a “standard drink” is of greater volume than it is (ie. people often pour more than 1 standard drink as their usual glass of alcoholic beverages). This is the topic that I will address here.

One issue that we need to get out of the way first is: How much alcohol is too much for a driver? It has been suggested, for example, that the U.S. drunk-driving BAC (blood alcohol concentration) limit is too high. Utah is apparently the only state with a 0.05% BAC limit when driving, and everywhere else in the U.S.A. it is 0.08%.

When I was young, Australia brought in that same 0.08 limit, but later lowered it to 0.05, which is therefore what I find “normal” — one serious drink is all you can safely have. I now live in Sweden, where the limit is 0.02 — you can’t safely drink at all, if you are the designated driver for your outing group. Apparently, there are more than 30 other countries with similar low limits (Drunk driving law by country).

There are a number of web pages that provide data for blood alcohol percentage, for both males and females, based on body weight and the number of standard drinks consumed; for example: BAC facts: impairment starts at the first drink; and Blood alcohol level chart.

So, what is this “standard drink”? Sadly, there is no accepted international definition for how a standard drink is defined in terms of the amount of pure alcohol (ie. ethanol), and so it can potentially vary from country to country. However, according to the U.S. National Institute on Alcohol Abuse and Alcoholism, a standard drink is defined as containing 14 grams (0.6 ounces) of pure alcohol, which is a widely accepted version.

Using this definition yields the above graph, showing how the number of standard drinks relates to the alcohol content of the wine, which can vary greatly (wine typically ranges from 9% to 16% alcohol by volume, ABV). That is, the higher the alcohol content then the greater is the number of standard drinks that the bottle contains, and the smaller volume is the size of the standard drink that can be taken from it.

For example, as shown in the graph, there are roughly 5 standard drinks in a bottle of 12% ABV wine, or a standard drink of wine taken from that bottle is 5 fl.oz (150 ml). Alternatively, there are 5.5 glasses in a bottle of 13% wine, and 6 glasses in a 14% wine bottle, and the glass volumes are correspondingly smaller.

Obviously, then, for each bottle of wine we are getting ready to consume (either alone of with others!) we need to check the ABV (always on the label), and then we will know how many “glasses of wine” it contains. This will give us an idea of what situation we are now in.

When we are judging this in real life, however, the shape of the wine glass and its volume can affect our judgement. This is illustrated in the next picture, which shows what a 5 fl.oz pour looks like in five different glasses. Note that wider glasses typically receive inordinately larger pours. It has even been reported that the amount of wine poured can be affected by whether the glass is held in the hand or stands on a table, and whether the wine is white versus red (whites typically get bigger pours); and, of course, it is reported that: Risky drinkers underestimate their own alcohol consumption.

Returning to the initial topic, we also need to consider: How quickly does the alcohol disappear from the body and can you sober up faster? Apparently, the liver breaks down alcohol into other substances at a rate of about one drink per hour, although there are big differences between individuals. Sadly, alcohol and its byproducts can continue to be detected in your system, so that you could fail a breath test several hours later.

The current dietary guidelines for healthy alcohol consumption by adults in the United States differ between sexes:
 — women should consume no more than 1 standard drink per day and a maximum of 7 drinks per week
 — men should consume no more than 2 standard drinks per day and a maximum of 14 drinks per week.

In comparison, in Australia and New Zealand the guidelines are that:
 — a woman should have no more than 2 standard drinks daily, no more than 10 per week, and no more than 4 at once
 — a man should have no more than 3 standard drinks daily, no more than 15 per week, and no more than 5 at once.

It is for these reasons, as well as simply general health concerns, that sales of low- and no-alcohol wines have been growing briskly in recent years, as wine drinkers now pay more attention to what goes into their bodies (Why major players are investing big in wine with little, no alcohol).

The latter is a tricky business. There are two main ways to produce lower-alcohol wines — harvest grapes at lower sugar levels, and remove the alcohol after fermentation. This is a topic for another post.