A Lot of Bottle

Caroline Gilby MW on why UK wine drinkers are yet to be weaned off the bottle

Have you ever stopped and wondered why most wine still comes in glass bottles at least in the UK? In some countries, particularly in Scandinavia, bag-in-box has taken well over 50% market share but in the UK, we are still firmly wedded to glass.

Glass is heavy, breakable and an awkward shape so there must be more than simply tradition in our resolute adherence to bottles. Here, we don't have the option of nipping to the local wine co-operative and filling up a plastic jug from a petrol pump-style nozzle. And anyone who has tried this when on holiday will know that wine sold this way only lasts about 48 hours before it starts to turn into vinegar. So wine has to be packaged and sealed in a way that gets it to the end consumer as the winemaker intended, which may be weeks, months or years in the future.

Different wine bottle shapes

The short of it

Most wine in the UK is still sold in glass bottles and it's not simply about tradition and image. Glass is strong, inert, doesn't let oxygen in and doesn't react with strongly acidic wine. It can also be coloured to protect wine from damage called light strike due to exposure to ultra violet light. Clear glass is particularly bad for this, though rosé producers like to show off their pretty pink colours. The next decision for the producer is what sort of closure to use – varying from traditional but potentially inconsistent natural cork to modern technical and synthetic options, plus screw-cap and glass. And then controlling the bottling process itself requires care – all to make sure the hard work from the vineyards and cellars are not lost before it reaches your glass. Glass has disadvantages too as it is heavy, breakable and awkwardly shaped, and alternatives like bag-in-box, cartons and cans all exist but don't threaten the rule of glass – at least in the UK.

The Long of It

Keeping it fresh

Wine is inherently unstable and only an interim stop on the way from grape juice to vinegar and the trick is to keep it there. Winemakers need to keep microbes like yeast and bacteria out as well a oxygen which can damage colour and flavour. It is harder to do this than you might imagine, so usually a judicious dose of preservative gets added into the mix too.

Here sulphur dioxide (sometimes in sulphite form) comes into its own, with its multifunctional roles of mopping up and binding oxygen before it can damage the wine and stopping microbes from growing. It's very hard indeed to make stable wine with no added sulphites, so you will almost always see a legally required declaration of 'contains sulphites' on just about every bottle you can buy.

The other problem with wine is that it's really quite strongly acidic (pH ranges are around 2.9 to 4.0) which makes it quite reactive, so it needs to be packaged in something it won't react with. Glass works well for this (think back to school when strong acids like hydrochloric or sulphuric acid always came in thick glass flasks for the same reason). Occasionally, you can find wine in alternatives like aluminium cans, but these must be coated to protect the metal from acidic wine.

Another useful feature of glass is that it's quite strong (think how hard it is to smash a bottle when you hurl it into the bottle bank) unless you catch it on a corner. This property is particularly useful for sparkling wine where it has to resist up to six atmospheres of gas pressure. (Indeed it was strong glass from English coal-fired furnaces that first enabled bottle-fermented sparkling wine to be produced regularly in the 17th century – you can read more on that here).

It's also useful to be able to colour glass – brown and that olive-green tone known as 'feuille morte' or dead leaf are particularly good at protecting wine from a condition called light strike. This is caused by ultraviolet light degrading certain amino acids in wine and producing unpleasantly smelly compounds (smelling like cheap lager, rotting cabbage or skunk, if you've ever had that particular pleasure!) This can happen within just an hour or two of exposing wine to light and that includes artificial light in shops (a great reason for buying your wine direct from the warehouse).

Clear glass is awful for wine. At best, it only blocks about 10% of damaging wavelengths of light (compared to brown or amber glass blocking 90% and green glass over 60%). But clear glass is incredibly trendy, particularly with the growth of rosé consumption where producers want to show off its pretty colour and there seems to be a strong trend for more entry-level whites to appear in clear glass too. Marketing is clearly winning over wine quality.

How best to seal your bottle

Different corks and closures

Having chosen to go with glass, the next issue is what to seal the bottle with. The arguments for and against natural cork versus screw-cap have been discussed widely so I won't go into lots of detail here. (You can read more on closures in this article).

Natural cork is a historic and traditional choice and still in demand in many markets. It is elastic enough to seal even if bottle necks vary (inconsistently manufactured bottlenecks were more of a problem in the past than now) and forms a seal along the whole length of the cork, which may be as long as 49mm.

Cork – natural but inconsistent

One issue is the inconsistency of natural product, so its sealing ability may vary, and if allowed to dry out, its elasticity can fail and the result is random oxidation.

The other issue is contamination by cork taint, that mouldy damp cellar smell caused by Trichloroanisole or TCA. Not only does it smell bad at high levels but even below detection threshold it can flatten fruit and make wines seem dull.

Technical corks (such as Diam) have been developed to guarantee no TCA by using ground up particles of natural cork material, cleaned with super critical carbon dioxide to remove all TCA taints, then bonded together to offer consistent elasticity and guaranteed sealing properties. There are also various synthetic closures from extruded plastics and recently a version derived from sugarcane waste to overcome the issues of natural cork.

It is also worth noting that the space between the top of the wine and the cork is quite small with these closures so even if bottled with air, it's not a huge amount of oxygen, and anyway most producers would use an inert gas like nitrogen to fill this headspace.

Diam Corks © RK Le Studio
Diam cork showing what it is made of

The Diam process chops cork into pieces and sorts the superior, highly elastic, suberin component from the less elastic lignin, which is discarded.

Screwcaps are surely the solution?

Screwcaps Screwcaps, no longer such a contentious a choice of closure, at least in the UK

Switching to screwcap is not as simple as it may seem. It requires a different bottle mould and more precise bottle manufacture as the seal is just the very rim of the bottle, and usually an expensive new machine to fit them.

Then the winemaker may have to adapt his or her winemaking to allow for the very hermetic nature of many modern screwcaps and also the much bigger headspace between the liquid and closure. Issues with a fault called reduction can occur – giving unpleasant smells of hydrogen sulphide, struck match and wet hair. Leading screwcap manufacturers have now developed liners with varied permeability to oxygen to also give winemakers more choice.

The old-fashioned screwcaps that were used on the likes of Lambrusco and Liebfraumilch years ago provide very little oxygen barrier and are only suitable for wines with the very quickest turnover s it has taken time for this poor reputation to be overcome.

What other choices are there?

The other closure option is glass – which looks nice and is inert in itself, but I have started to hear producers raise concerns about longevity. The actual seal here is a resin polymer O-ring on the rim of the bottle and there are worries that this can harden and let in oxygen. So even choosing how to close your bottle is a complex technical decision, never mind the marketing issues.

And what of the alternative packaging?

Soave Bag-in-Box Producers of premium Soave, Coffele have been selling their wine in a bag-in-box format for a while now and we are looking at trialling it later this summer.

Certainly in the UK, Tetra Pak, plastic pouches and bag-in-box are available, but haven't caught on strongly, and are mostly associated with cheaper wine. These packs depend on a thin metallic layer sandwiched between layers of plastic for their oxygen barrier and this can be prone to flex cracking.

These microscopic tears in the metal allow oxygen in and damage the wine, and with bag-in-box, taps can also be a weak point for allowing oxygen into the wine. There is also a risk of expansion and leakage if temperature varies, or if microbes get in and start a second fermentation, or if crystals form in the tap. It is important with these packages to ensure quick turnover and to be very careful about handling and filtering the wine to a sterile level. It's also important to have good levels of preservatives, particularly sulphites, to limit oxygen damage. And a final point is that most local authorities in the UK will provide limited recycling for these alternative packages, but glass recycling is easy to find.

The final part of the process is getting the wine from a barrel or bulk tank into bottle via the bottling machine. Until the cork is inserted or cap fitted, the wine is vulnerable to contamination or air exposure, so it is very important to monitor the running of the bottling machine to avoid risks. Breakages, contamination by insects or stray microbes, or oxygen ingress are potential failures. It's not a glamorous phase of wine production but is vitally important to ensure that all the hard work from the vineyard and through the winemaking and ageing process is not lost before the wine makes it to the consumer's glass.

The wine industry is often accused of failing to innovate, but given the technical difficulties of handling wine, combined with consumers (and producers) who seem to be largely happy with a bit of tradition, it’s not hard to see why glass still rules in the world of wine.

Caroline Gilby MW

June 2017

Caroline Gilby MW

Caroline Gilby is a Master of Wine and a scientist by training. She is a wine writer with a passion for the wines of Central and Eastern Europe and contributes to several wine books, magazines and websites.

Read more articles by Caroline Gilby MW >

Read more about Diam corks here >

Read more on bottling wine here >

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