can

Canning is a method of preserving food in which the food contents are processed and sealed in an airtight container (jars like Mason jars, and steel and tin cans). Canning provides a shelf life that typically ranges from one to five years, although under specific circumstances, it can be much longer. A freeze-dried canned product, such as canned dried lentils [小扁豆], could last as long as 30 years in an edible state.

A Mason jar — named after John Landis Mason, who patented it in 1858 — is a molded glass jar used in home canning to preserve food. The jar's mouth has a screw thread on its outer perimeter to accept a metal ring or "band". The band, when screwed down, presses a separate stamped steel disc-shaped lid against the jar's rim. An integral rubber ring on the underside of the lid creates a hermetic [密封的] seal. The bands and lids usually come with new jars, but they are also sold separately. While the bands are reusable, the lids are intended for single-use when canning. Glass jars and metal lids are still commonly used in home canning while they have been largely supplanted by other methods for commercial canning (such as tin cans and plastic containers).

In 1974, samples of canned food from the wreck of the Bertrand, a steamboat that sank in the Missouri River in 1865, were tested by the National Food Processors Association. Although appearance, smell, and vitamin content had deteriorated, there was no trace of microbial growth and the 109-year-old food was determined to be still safe to eat.

During the first years of the Napoleonic Wars, the French government offered a hefty cash award of 12,000 francs to any inventor who could devise a cheap and effective method of preserving large amounts of food. The larger armies of the period required increased and regular supplies of quality food. Limited food availability was among the factors limiting military campaigns to the summer and autumn months. In 1809, Nicolas Appert, a French confectioner and brewer, observed that food cooked inside a jar did not spoil unless the seals leaked, and developed a method of sealing food in glass jars. Appert was awarded the prize in 1810 by Count Montelivert, a French minister of the interior. The reason for lack of spoilage was unknown at the time, since it would be another 50 years before Louis Pasteur demonstrated the role of microbes in food spoilage.

The original fragile and heavy glass containers presented challenges for transportation, and glass jars were largely replaced in commercial canneries with cylindrical tin can or wrought-iron [锻铁] canisters [小罐] (later shortened to "cans") following the work of Peter Durand (1810). Cans are cheaper and quicker to make, and much less fragile than glass jars. Glass jars have remained popular for some high-value products and in home canning. Can openers were not invented for another thirty years – at first, soldiers had to cut the cans open with bayonets or smash them open with rocks. Today, tin-coated steel is the material most commonly used. Laminate [层压] vacuum pouches are also used for canning, such as used in MREs and Capri Sun drinks.

MRE is meal ready to eat (a precooked and prepackaged meal used by US military personnel). Capri Sun is a German juice concentrate drink.

• a can of worms = complicated problem
• carry the can (for sb/sth) = to be the person who has to take the blame for sth even if it was not their fault, or not their fault alone

六级/考研单词: seal, jar, tin, edible, patent, mold, screw, thread, outer, lid, rim, integrity, rubber, wreck, nationwide, vitamin, deteriorate, trace, devise, regulate, militant, autumn, spoil, leak, interior, fragile, cylinder, prolong, smash, vacuum, worm, complicate