Which glass do you use for what?

ISO 3591 from June 1977 describes the glass used for sensory examination of wine: a bowl in the shape of an elongated egg, on a stem with a foot.

The standard requires colourless, transparent glass without grooves and air bubbles, and a regular, smooth and rounded rim without unnecessary thickening. For crystal glass the standard sets hard limits: more than 10 percent metal oxides, a relative density of at least 2.45 and a refractive index above 1.520.

On use, the standard is equally concrete: you pour 50 millilitres, enough for two sips of 25 millilitres. Measurements in scientific work give the glass a capacity of 215 millilitres, an opening of 44 millimetres, a bowl height of 92 millimetres and a greatest bowl diameter of 65 millimetres.

A bowl that narrows towards the top keeps the volatile aroma compounds together above the wine instead of letting them blow away.

ISO itself names this as the reason for the shape: the opening is narrower than the bulbous part, to concentrate the bouquet while letting the full body of the wine come out.

Researchers at the Tokyo Medical and Dental University made this visible in 2015 with a camera that images ethanol vapour. At 13 degrees the alcohol concentration in the middle of a wine glass was lower than along the rim, which created a ring. In a martini glass and in a straight glass that ring did not appear, nor at a higher temperature. The shape of a wine glass therefore keeps the alcohol vapour out of your nose while you assess the aroma.

Yes, in controlled trials both the composition of the vapour above the wine and the judgement of tasters differ per glass shape.

In a 2001 study in the Journal of Wine Research, three glasses were set side by side: the ISO glass of 215 millilitres with an opening of 44 millimetres, a Burgundy glass of 730 millilitres with an opening of 69 millimetres and a Chardonnay glass of 350 millilitres with an opening of 62 millimetres. Each glass was filled with 40 millilitres of wine.

The ratio between the largest bowl diameter and the opening correlated strongly with perceived aroma intensity: a correlation of 0.99 for red wine and 0.89 for white wine. For color intensity it worked exactly the other way around, with 6.1 in the small ISO glass against 3.2 in the large Burgundy glass for red wine.

In a study in the American Journal of Enology and Viticulture from 2012, the glass shape made hardly any difference at zero minutes, but after five and ten minutes it did. The Bordeaux glass and the ISO glass brought out fruity notes, while another red wine glass emphasised the warm, alcoholic side.

For each type of wine, choose a glass whose bowl is clearly wider than the rim, and let the size move with how much air the wine needs.

• Red wine with firm tannin: a roomy goblet. In the 2001 study, the 730-millilitre glass with an opening of 69 millimetres received the highest aroma intensity.
• White wine: a medium size, in that study 350 millilitres with an opening of 62 millimetres. Smaller stays cold longer.
• Tasting and comparing: the ISO glass of 215 millilitres, because then everyone measures the same.
• Sparkling: a narrow, tall glass, so the wine stays cold and the bubbles have a long path.

Never fill a glass to the rim. ISO 3591 assumes 50 millilitres in a glass of 215 millilitres, roughly a quarter. If you keep to that ratio, there is room in which the aroma collects and you can swirl without spilling.

A stem keeps your hand off the bowl, and that is no detail: the temperature of the wine determines how much alcohol vapour hangs above the glass.

In the 2015 camera study, the ring of lower alcohol concentration in the middle of the glass disappeared as soon as the wine became warmer than 13 degrees. The vapour then spread more evenly and the ethanol came more strongly to the fore, which makes the smell of the wine itself harder to read.

ISO 3591 also prescribes colourless glass, so that you can judge the colour, plus a smooth and rounded rim without thickening. Coloured glass or a thick rim both rule that out. A simple, clear glass on a stem therefore meets everything the standard asks of you.