There are some things we accept as fact without ever really questioning them. Chips taste better at the seaside, tea tastes better from your favourite mug (and with biscuits), and Coke tastes better from a glass bottle.
Taken cold from a fridge with beads of condensation running down the outside. The metallic crack of the cap coming off, the hiss of escaping gas and then that first mouthful which somehow seems colder, sharper and fizzier than the same drink poured from a two-litre plastic bottle.
But Coke isn’t the only drink that seems to do this, water does it too.
Given the choice between an icy glass bottle of mineral water and its plastic equivalent, many of us would instinctively reach for the glass because somehow, even water seems to taste better.
So why does Coke taste better in a glass bottle?
The sensible answer, and probably the first one you’d come to, is that glass must preserve it better. And you would be correct, as there is some science behind that – but it turns out that’s only half the story.
Because when we drink something, we aren’t just tasting the liquid, we’re tasting the bottle too.
Does glass actually change the taste of Coke?
Glass is an excellent barrier. Whereas the very easy to remember polyethylene terephthalate, better known as PET and the plastic used for most soft-drink bottles, isn’t completely impermeable to gases.
Over time, carbon dioxide can pass through PET, meaning the drink can gradually lose some of the gas that gives Coke its bubbles. Glass itself is, for practical purposes, impermeable to CO₂, although gas can still potentially escape through its closure.
How quickly any of this happens depends on the bottle, its thickness, storage temperature and how long it has been sitting around – but going flat isn’t the only concern.
Dissolved carbon dioxide contributes to acidity and to the physical bite and prickle we experience when drinking something fizzy. Take enough of that away, and if you’ve ever had flat Coke, you’ll know, you’re left with very sweet brown liquid that just isn’t refreshing. Although, anecdotally at least, flat Coke has long had its defenders as a hangover cure, so perhaps it still has its uses.
There are other, much smaller interactions too, including something known as “flavour scalping“.
Essentially, the bottle can steal tiny amounts of your drink’s flavour. Certain aroma molecules can be absorbed by polymers, the long chains of molecules that plastics are made from, in the packaging itself.
How much gets taken up depends on the particular plastic, temperature, length of storage and the flavour compound itself. One aroma particularly susceptible to this is limonene, the compound responsible for much of the familiar citrus smell of oranges, lemons and other citrus fruits. It’s worth nothing, though, that PET is actually much better at resisting this than some other plastics.
The opposite journey is possible too. Tiny amounts of compounds associated with packaging can migrate into its contents. None of this means plastic-bottled drinks routinely taste of plastic. In commercial conditions these effects can be very small, and packaging is specifically designed to protect what is inside it. But it does mean packaging can alter the liquid inside, whether by allowing things out, taking flavour compounds up or, in tiny amounts, putting things in.
So far, then: 1–0 to glass.
But physical changes to the liquid aren’t the whole story – and water gives us a particularly interesting way of seeing why.
Why does cold water taste better?
Water isn’t actually tasteless, as our editor continues to insist while berating anyone in the vicinity who says otherwise.
Different waters contain different combinations and concentrations of minerals, picked up from the rocks and soils they have passed through. These can make one water seem softer, another saltier, another slightly bitter or metallic. Put a few water obsessives around a table and things can become surprisingly heated for a discussion about H₂O.
But take exactly the same water and change its temperature, and our experience of it changes too.
If you’ve ever wondered why cold water tastes better, the interesting thing is that the science isn’t really about cold water having a fundamentally different flavour – it’s about what coldness does to the experience of drinking it.
Researchers have found that cold water can reduce thirst more effectively than the same amount of warmer water. In one experiment, thirsty participants drank 400ml of water under different sensory conditions. Cold water reduced how much they subsequently wanted to drink compared with room-temperature water.
Perhaps stranger still, coldness seems to affect our judgement of how much we’ve drunk.
When participants couldn’t see how much liquid they were consuming, making the drink feel cold in the mouth increased their estimate of how much they had swallowed. So did carbonation. Across those sensory manipulations, perceived volume could increase by around 22 per cent.
In other words, your brain can apparently be convinced you’ve drunk more simply by making the experience colder or fizzier. Not great news for our editor, who drinks exclusively sparkling water and is notoriously bad at remembering to hydrate.
Researchers think sensations such as oral cooling and the physical irritation or “bite” of CO₂ may be among the signals our brains use to judge drinking and the satisfaction of thirst.
But what has any of this got to do with glass bottles? Well, quite a lot.
How quickly a drink itself warms depends on the whole container and its surroundings, including its thickness, shape and conditions, rather than simply whether the bottle is glass or PET. But what chilled glass does particularly well is feel cold.
Glass transfers heat more readily than plastic, so two bottles kept at exactly the same temperature can feel quite different in our hands. Pick up the glass one and that hard, cold surface is giving your brain another signal associated with refreshment before you’ve even taken a sip.
Then the glass touches your lips and the cold water cools your mouth. Suddenly, the experience we casually describe as water “tasting better” involves rather more than taste.
So, 2–0 to glass for refreshment although hydration may wish to appeal the decision.
So does Coke actually taste better from a glass bottle?
Unlike bottled water, where the liquid itself can vary considerably depending on its source and mineral composition, Coke allows us to look at the question under rather more controlled conditions.
Take the same cola and change the vessel it is drunk from, and we can start to separate what the liquid tastes like from what the container might be making us think it tastes like.
And conveniently, someone has done exactly that.
In 2017, researchers gave 100 people cola and sparkling water in three different vessels: a familiar curved cola glass, an ordinary water glass and a plastic bottle.
The tasting wasn’t blind – participants could see the vessel, hold it and drink directly from it, but that was the point.
The cola’s aroma was perceived as more pleasant and more intense when it was served in the familiar cola glass, and its sweetness was also rated differently depending on the vessel.
But one result that rather inconveniently ruins any neat argument for the superiority of glass is that both the cola and sparkling water were actually rated as more carbonated when drunk from the plastic bottle.
Whether more carbonation makes for a better drinking experience is another question. At higher levels, that carbonic bite can start to feel sharp or even aggressive, but who are we to judge. As with most things involving taste, “more” and “better” aren’t quite the same thing.
That brings us up to 3–0.5 to glass, with the half point depending on how fizzy you like your Coke.
This isn’t the only research to find that the container we drink from can influence our perception of what’s inside it. Shape, material, weight and what we expect from a particular vessel can all become part of the experience.
Which brings us to the rest of our senses.
We taste with more than our mouths
Opening Coke in a glass bottle is physically a different experience from opening its PET counterpart. One involves levering a metal crown cap from a rigid glass bottle, the other twisting a plastic screw cap.
Both release pressure with a hiss, but the little performance surrounding it is different.
There isn’t evidence showing that the particular crack-pssscht of a glass Coke bottle makes the Coke taste better, but what research does show is that the sounds drinks make when they’re opened and poured can give us information about what we’re about to drink. As such, sounds shapes our expectations before we’ve taken a sip, which can ultimately shape our perception of the drink itself.
Then there is the visual aspect.
Glass comes with baggage – it’s heavy, rigid and breakable. We encounter it around wine, spirits, restaurants and expensive things. Plastic, meanwhile, has spent decades becoming the practical material in which we buy drinks cheaply and in enormous quantities.
A two-litre plastic bottle of Coke says children’s birthday party or family barbecue. A little glass bottle of Coke says this one’s just for you to savour. One is a supply of Coke, the other is a serving.
We’ll call that one a draw, and split the point as they both have their place. Final score: 3.5–1 to glass.
By the time a Coke reaches our tastebuds, then, the rest of us has been remarkably busy. We’ve seen the bottle, felt its weight and temperature, heard it open, smelled what’s inside and already formed an idea of what drinking it is going to be like.
Suddenly, separating the taste of Coke from the experience of drinking Coke becomes rather difficult.
So, is it all in our heads?
There are physical differences and there are psychological ones, but trying to decide which counts as the “real” taste rather misses the point.
Taste doesn’t happen in a tiny laboratory inside our heads, objectively analysing a liquid while politely ignoring the cold bottle in our hand, the hiss when we open it, the smell reaching our nose and the glass against our lips – those things are part of drinking it.
But if you’re going by our scoring system then yes, categorically, Coke tastes better from a glass bottle. The numbers don’t lie.
Next up in things we all accepted without asking why: why do we drink orange juice for breakfast?
And if all this has got you thinking about what liquids actually taste like, may we suggest another rabbit hole: what does wine taste like? a beginners guide.