Bore control, cork types & extraction
Six things the bore decides that the cork cannot.
A cork seals because it is compressed into a bore narrower than itself and pushes outward for years afterward. That makes the bore diameter and its consistency the most important dimensions on the bottle: too wide and the seal is weak, too narrow and the cork is over-compressed and hard to extract, and variation between bottles produces both.
The bore is the closure specification
A cork is compressed on insertion and relies on its own recovery to hold the seal. Wine bottles work to a bore around 18.5 mm for standard corks, and a bore that drifts within a delivery gives some bottles a weak seal and others a cork that will not come out. Bore consistency matters more than nominal size.
Cork types behave differently in the same bore
Natural cork recovers strongly and varies piece to piece; agglomerate is more uniform and recovers less; technical corks combine a molded body with natural discs. Each compresses and rebounds differently, so a bore that suits one may over- or under-compress another. Bottle and cork are chosen together rather than in sequence.
Extraction force is a customer-facing number
A cork that takes excessive force to pull, or one that breaks, is a consumer complaint about the wine rather than the closure. Extraction force follows from bore, cork type and how long the bottle has been standing, and it is measured on aged bottles rather than freshly corked ones where the cork has not yet relaxed.
T-top corks are a separate finish
A reclosable T-top used on spirits and oils has a shorter shank and a head that rests on the lip, and it works to a different bore and lip geometry than a driven wine cork. A bottle made for one will not take the other properly, and specifying only cork finish leaves that distinction undefined.
The lip has to survive the corking machine
Driving a cork applies real force to the lip, and a chipped or uneven lip both leaks and can crack under the corker. Lip quality is therefore inspected more closely on cork-finish bottles than on crown or screw formats, and a supplier's consistency there is what separates a smooth bottling run from a stopped line.
Bottles are stored on their side for a reason
A natural cork dries and shrinks if it is not kept in contact with the wine, which loosens the seal over years. That is why cork-finished wine is binned horizontally, and it is a genuine functional difference from screw cap or crown bottles that can be stored upright without consequence.
