This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Where it is a question of retaining the gas in the beverage, an inferior cork should never be used. Mineral waters are the most severe on corkwood, and, unless the best grained cork is obtained, the life of the liquid is bound to escape. The same is true of champagne. The most carefully selected corks are reserved for this wine. Bottlers may consider it shrewd economy to purchase half size or low grade corks, and imagine the consumer is indifferent to a leaky or an effective stopper. The contrary is the fact, however. The cork cannot be superseded by any as yet discovered material or contrivance for stoppering bottles whose contents are to be preserved for an indefinite time. Neither can a high grade of beverage be retained uncontaminated for other than quick consumption. Many are disposed to think that if the bottle is only stoppered, it makes precious little difference what kind of a cork is employed. Carbonated beverages require a firm, close-grained cork, and not a soft, spongy article. Carbonic acid gas will escape through a poor cork in no time, and as the life of a drink depends altogether upon its gaseous nature, an inferior cork cannot but work damage to the goods. The same holds true of steamed bottled beer. The steam softens the cork, and unless it is of good quality the liquid suffers in the loss of its gas.
The manufacture of corks in this country is carried on almost entirely by machinery, and is the kind used by bottlers to a large extent. Were it not for machine-cut corks the bottling trade would be compelled to pay enormous prices for their corks, and patent stoppers would be its only salvation. Until a comparatively recent date corks were cut by hand, and it took an experienced workman a whole day to finish a thousand marketable corks, with great waste of material. To-day a machine run "by steam and attended by a small girl does fifty times the amount of work with unerring precision and the smallest possible waste of material. Corks are made in innumerable sizes and grades, from the size of a pin-head up. Every cork has to be handled three and four times in the 25 manufacture - once in blocking, once in cutting, once in tapering, and the last time in assorting one grade from the others. A machine-cut cork will always fit the bottle it is made for.
The imported corks come chiefly from Spain and Portugal, though Germany sends a lot to this country also.
The finest grade of corks are hand-cut entirely, and are used to the exclusion of all others for champagne. Some of our largest beer and mineral-water bottlers prefer a hand-cut cork, because of the uniform good quality.
There is no disputing the fact that corks will always remain in use by bottlers, notwithstanding the apparent activity in patent bottle stoppers. The trade cannot close its eyes to the objections raised against the bottler by consumers, which the former never meets with, and bottlers are advised to buy none but good quality corks for the proper preservation of a fine grade of beverages, either carbonated or fermented.
Select corks of soft wood, light color and as little porous as possible. Red corkwood is not elastic, very porous and brittle, and such corks are easily torn and cut in the bottling machine and in extracting them from the bottle, thus causing the beverage to be specked with pieces of rotten cork.