Corkscrew (How Products are Made)
Uncorking a bottle of wine presents a challenge. There is no way to grip the cork, which is completely recessed in the bottle's neck. Furthermore, pulling the cork out requires a force of 25-100 lb (110-450 N), depending on whether the cork is moist or dry (from the bottle being stored on its side or upright, respectively).
A corkscrew is an implement designed to mechanically remove the cork. It consists of a handle and a helical or screw-like blade that is commonly called a worm. (A corkscrew without a center post is actually a helix, with all the coils having the same radius; however, it is often called a spiral, even though that term technically means a curve with a constantly changing radius.) Screwing the worm through the center of the cork allows the corkscrew to grip the cork internally. Pulling on the handle draws both the corkscrew and the cork out of the bottle. Some corkscrews employ levers, springs, gears, or other mechanical devices to lessen the amount of force needed to pull out the cork.
Corks were used to seal bottles in the ancient Greek and Roman civilizations. Removing them was not difficult, however, because they extended above the rim of the bottleneck far enough to be grasped firmly. After the fall of Rome in the fifth century, cork bottle stoppers disappeared from use for a thousand years.
During the late sixteenth century, cork bottle stoppers reappeared as in England. Again, no special implement was required to remove them, since they were tapered in shape and protruded a comfortable distance from the vessel. Blown-glass bottles began to replace barrels and skins as wine storage vessels. The bottles consisted of a squatty chamber topped with a tapered neck. These "shaft and globe" bottles were sealed with tapered corks wrapped with waxed linen, making it easy to grasp and remove the stoppers.
Between the late seventeenth and eighteenth centuries, two developments proceeded simultaneously. It is unclear which was the cause and which was the effect. Manufacturers began mass-producing bottles of uniform size by pouring molten glass into molds rather than hand-blowing bottles one at a time. This manufacturing method allowed production of tall, slender bottles with straight sides and cylindrical necks. This shape of bottle could be laid on its side for storage and shipment, an advantage that boosted the international wine trade. Tighter seals were required so the bottles would not leak, a challenge solved with cylindrical corks that were compressed prior to being forced into the bottle necks. Because of their tighter fit, these corks were harder to remove than the earlier, tapered versions.
The parallel development was the invention and evolution of the corkscrew. It began with the adaptation of the gun worm, a long-handled, helix-tipped tool that could be inserted in the barrel of a musket or pistol to retrieve wadding and unspent bullets. The earliest written reference to a true corkscrew dates back to 1681. Until 1720, when the word "corkscrew" came into use, the tools were called bottlescrews. Bronze and iron were sometimes used to make the worm, but steel became more popular because of its greater strength and its ability to retain a sharp point.
Image Pop-UpExamples of mandrels.
During the early 1700s, pocket corkscrews became popular. A metal or wooden sheath covered the spiral, protecting the worm and the owner's pocket. In some models, the sheath could be inserted in a loop at the end of the worm's shaft to provide an effective T-handle for the corkscrew. During the latter half of the eighteenth century, corkscrews became increasingly elaborate, using materials like silver, gold, exotic woods, ivory, and jewels. Multipurpose tools often combined corkscrews with devices such as pipe tobacco tampers, nutmeg graters, seals, and folding pocket knives. Dainty corkscrews were produced to open small bottles containing perfumes and medicines, for corks were the preferred sealer for all types of bottles until cork-lined metal bottlecaps became popular 1890.
The first corkscrew patent was issued in England to Reverend Samuel Henshall in 1795. It was a simple, T-shaped device with a steel worm protruding perpendicularly from the center of a handle made of bone or wood. Like many corkscrews of that period, brush bristles extended from one end of the handle; the brush was used to clean dust and sealing wax from the cork before opening a bottle. The innovative feature of Henshall's design was a flat disk, or button, mounted on the shaft connecting the worm to the handle. This kept the worm from being screwed too far through the cork; it also established a firmer contact between the corkscrew and the cork, making it easier to pull out the cork.
In 1802, a more complex mechanical corkscrew was patented by British engineer Edward Thomason. A bell-shaped cylinder surrounded the worm; setting the bottom of the cylinder on the top of the bottleneck positioned the worm vertically above the center of the cork. After the spiral had completely penetrated the cork, continued turning of the handle pulled the cork out of the bottle. The user could then hold the corkscrew over a fingerbowl, turn the handle in reverse, and automatically eject the cork without soiling his or her fingers.
A flurry of inventive activity in the late 1800s produced many variations of corkscrews enhanced with levers, gears, springs, and secondary screws to raise the cork out of the bottle. In just over 100 years following the first patent, more than 350 corkscrews patents were granted in England and some 250 were awarded in the United States. One of the more prolific American inventors in the field was W. Rockwell Clough of New Jersey. In 1876, he developed a machine that could bend a single piece of wire into a complete corkscrew; at one end of the helix, the wire was twisted into a fingerloop handle. In a subsequent refinement, he added a wooden sheath so the corkscrew could be carried in a pocket. After the metal bottlecap became popular, he developed a bottlecap remover and attached it to the end of the sheath. Clough's company eventually produced an estimated one billion inexpensive corkscrews, many of which were advertisements with brand names imprinted on the sheath.
Around the end of the nineteenth century, British corkscrew maker Thomas Truelove used a forming machine to forge steel worms. A grooved mandrel (forming rod) was rotated with a hand crank while a red-hot steel rod was inserted through an eyelet.
One of the more significant corkscrew inventions of the twentieth century was the Screwpull, patented by Texas engineer Herbert Allen in 1978. Placing the device on top of the bottle, the user simply pushes a lever down and then pulls it back up to effortlessly insert the worm and extract the cork.
Steel remains the preferred spiral material, with 440C stainless steel and tempered low-carbon steel being among the most popular choices. Levers and gears may be made from steel or from cast zinc alloy. Handles can be made from many materials, including common or exotic woods, bone, plastic, or various metals.
There are two categories of worms. The auger type is very much like a wood screw, with sharp-edged threads cut into a shank. If the threads are cut so deeply that they extend through the center of the shank, the worm may actually have a hollow center. Auger corkscrew manufacturers claim that their sharp threads help them penetrate corks more easily than round-edge worms. Critics contend that they tend to slice up the center of older corks, ripping out the soft middle of the cork without removing the entire stopper.
Worms with rounded edges are usually made by wrapping a very hot steel rod around a form to make a helix. The tip of the helix is sharpened to help it penetrate the cork easily. Some manufacturers pull the tip out of the helix's perimeter and position it in the center of its hollow core. This makes it easy to insert it into the center of the cork. However, the rest of the worm cannot exactly follow the path of the tip, so the center of the cork can be damaged by this type of corkscrew.
Some manufacturers of round-edge helixes score one or two shallow grooves into the outer surface of the worm to increase the gripping surface between the worm and the cork.
Round-edge corkscrew worms vary in design. They generally have between three and five turns in a helix that is about 2.5 in (6 cm) long. An open pitch comparatively wide spacing between turnss less likely to cause damage to the cork than a tighter spacing. The outer diameter of the worm is usually 0.3-0.4 in (0.8-1 cm).
The Manufacturing Process
Forming a helix
- 1 An open worm is formed by forging a steel rod into a helix shape. After sharpening one tip, the rod is heated to soften it for shaping. For example, 440C stainless steel is heated at 1,500°F (650°C) for 30 minutes, then at 2,100lF (1,000°C) for five minutes.
- 2 The hot rod is wound around a rotating cylindrical mandrel. To help guide the rod into a uniform spiral with the desired angle and spacing between successive coils, a grooved mandrel may be used.
- 3 Immediately after coiling, the spiral is hardened. This is done by reheating the worm to 1,500°F (650°C) and letting it cool slowly. Mild steel, on the other hand, is quenched by plunging the still-hot spiral into room-temperature water.
Forming an auger
- 4 An auger-type worm is formed by cutting threads into a tapered steel rod. With the rod secured in a lathe, a cutting head is mounted on the machine's lead screw, which pulls it parallel to the rod at a constant speed. This produces threads of the desired angle and spacing as the head cuts into the rod.
Finishing the worm
- 5 Whether it is a helix or an auger, the worm has a straight shaft extending beyond the coiled or machined section. This shaft, which will be inserted into a handle or other corkscrew mechanism, is prepared according to the customer's specifications. For example, it may be threaded, flattened, slotted, or drilled with a hole.
- 6 A surface treatment is usually applied to the worm to prevent corrosion. Typically, the worm is plated with chromium or nickel. To help it slide easily through the cork, the worm may be coated with a non-stick substance like Teflon or Silverstone.
Assembling the corkscrew
- 7 There are various ways to attach the worm to whatever type of handle or mechanism it will be mounted in. In the simplest case, insertion in a T-handle, two methods are used most commonly. The worm's flat or square shank may be inserted in a hole drilled in the handle and secured with two-part epoxy. Or a flat shank predrilled with a hole may be inserted into the handle and secured by driving a pin through the handle and hole.
Near the end of the twentieth century, some wineries began using synthetic corks. Because this material is harder than natural cork, popular corkscrew worms did not work well. Elongating the worm by adding an additional turn may have solved this problem. As improvements are made to synthetic cork composition, additional corkscrew modifications may be needed.
Where to Learn More
Giulian, Bertrand B. Corkscrews of the Eighteenth Century. Pennsylvania: White Space Publishing, 1997.
O'Leary, Fred. Corkscrews: 1000 Patented Ways to Open a Bottle. Atglen, PA: Schiffer, 1997.
Perry, Evan. Corkscrews and Bottle Openers. Buckinghamshire, Great Britain: Shire Publications, 2000.
"Corkscrews." (October 2000).
ArborFood Wine Web. http://arborfood.com (October 2000).