Different qualities of natural cork


There is a large range of different qualities of natural cork available – here we will discuss only natural cork (so not agglomerated or natural cork) and will focus on cork stoppers rather than other items made from cork.

Cork stopper quality starts with the quality of the bark – to make high quality cork stoppers you need bark that is generally smooth, with few holes or cracks and no disease or animal damage. Natural corks are made by cutting the bark into thin strips and punching the corks out, so if the bark itself is poor quality then there is no hope for the corks themselves (please note that when the cork bark is removed from a tree, the tree itself is unharmed and the bark will regenerate in around 9 years, making cork one of the most sustainable and environmentally industries in the world).

Cork bark when it is fresh off the trees from a harvest

Very high quality corks are made by highly skilled specialists that cradle the strips of cork in their hands to inspect the small imperfections and then choose the exact point where the punch will meet the cork to get the very best possible quality out of that particular piece of cork bark. Lower quality corks can be made with punching machines that just punch the corks from the centre of the strip.

Cork being punched from a strip of cork bark – note the minor imperfections in the cork surface that will detract from the quality rating of the cork stopper

Once they have been punched, the corks are fed through a laser sorting machine that analyses the surface the the individual cork and will separate them generally from super quality, down through first, second, third, through to 7th and rejects. The super quality corks can then be sorted by hand to split them into flor, extra and super and then the flor and extra corks can be additionally separated into “mirror” corks which have a perfectly smooth end to be presented to the cork screw when a wine bottle is opened.

Corks being hand selected

It is worth noting that even the very best flor corks will not be perfectly smooth – they will have tiny imperfections. As you go down through the qualities, the corks will of course have more of these imperfections, but down through to second quality there will be no major flaws in the corks. Third grade corks and lower will have more significant imperfections and often they are given surface treatments to improve the smoothness of the surface (including colmating where cork dust is effectively glued into the cracks and holes).

A decent bottle of wine should generally have a second quality cork or better, but going for extra or flor quality is really an exercise in aesthetics (to have an attractive looking cork that a wine connoisseur might appreciate) rather than having better mechanical qualities to seal the bottle better. With regard to spirits, the quality of the cork can be very important also – particularly with gins and other white spirits, where there is a risk that bad quality corks could colour the liquid, with the strong alcohol reacting with darker parts of the cork that can be revealed by cracks and holes. So for bottling white spirits you should use minimum first quality. For dark spirits, second quality and better should be fine. (It is worth noting that we also give our corks destined for bottling white spirits a special surface treatment to stop any transfer of colour).

A ‘flor’ quality cork, with an almost perfectly smooth surface

If you are buying a specific size of cork (commonly this would be for spirits bottles as wine bottles are very standard sizes) then it can be a good idea to buy a dual quality cork – so for example it could be super/first or first/second. Imagine that you are buying 10,000 first quality corks of a specific size – this would mean that the producer would take some quality of cork bark selected to be of more or less the right standard to make first quality corks and would produce say 15,000, knowing that say 2,000 would be super or better, and 3,000 would be second or worse. So these 5,000 corks would have to be repurposed for another order (or recycled in some other way). If you were to order a super/first, it would be a little more expensive, but the efficiencies that the producer would gain (in not having to exclude the 2,000 higher quality corks in this case) could be passed on to you the customer.

The final thing worth mentioning is that whilst in Portugal there is general consensus among the respect cork producers about what constitutes the various different qualities of cork, in some international markets there are wide variations. This has tended to happen because local distributors have attempted to pass off say second quality corks as first quality and this habit has become so ingrained that the bottlers in that country have ended in recognising a cork that should be classified as second as a first. This has only happened in some locations (south American countries tend to have this problem), whilst other countries such as the USA have not been “corrupted” in this way and still recognise the proper quality boundaries.