Wine kept in barrel deteriorates within months of the cask being broached, which limited how long any wine could usefully be held. The arrival of durable glass and a workable stopper changed what wine could be.
Barrels leak air continuously
Wood is permeable, and a barrel admits oxygen through its staves throughout its life. That exchange is useful during ageing and destructive once it continues indefinitely.
A barrel also loses volume to evaporation, leaving headspace that must be topped up constantly. Any neglect turns the wine oxidised and then vinegary.
Under those conditions wine was a seasonal product, consumed before the following harvest arrived. The idea of a wine improving for twenty years had no practical basis.
Coal-fired furnaces produced stronger glass
Early glass was thin, irregular and too fragile to be stacked or transported with confidence. Bottles served as decanting vessels rather than as storage.
Furnaces burning coal rather than wood reached higher temperatures and produced darker, thicker and considerably stronger glass. Bottles could then withstand handling, stacking and internal pressure.
Dark glass carried a second benefit that was not initially understood, since it shields wine from light-driven reactions that produce faults.
The cork completed the system
A bottle is only as good as its seal, and early stoppers of cloth, wood or wax were unreliable. Cork bark compresses and rebounds, which allowed a tight and durable closure.
Corked bottles could be laid on their sides, keeping the cork moist and preventing it drying and shrinking. Horizontal storage in turn made stacking possible.
Together these changes reduced oxygen ingress to a trickle, which is the condition under which slow reductive development occurs.
Consistent shapes made cellaring practical
Hand-blown bottles varied in size and shape, which made stacking unstable and quantities uncertain. Moulded production standardised both.
Cylindrical bottles could be binned horizontally in large numbers, and a cellar became a system rather than a store room.
Standard capacity also allowed wine to be sold by the bottle with confidence, which changed retail as much as storage.
Ageing became a commercial category
Once wine could reliably improve in bottle, merchants began holding stock deliberately and charging for the maturity they had financed.
Vintage variation acquired commercial meaning, since a wine could now be compared against the same wine from other years.
Nearly everything in modern fine wine, including cellaring, auction and the vintage chart, depends on a technology that started as a manufacturing improvement.