All cheddar cheese is, technically, aged cheddar. Aging the cheese after it has been formed and pressed is part of the process required to make it into an edible and tasty cheese. At a minimum, cheddar cheese must be left to mature for roughly three months to have the character expected of mild cheddar. There are, however, aged cheddar cheeses that have been allowed to mature for 10 years or longer. As cheddar is allowed to age, its flavor becomes sharper and sweeter and its texture grows harder and more brittle.
The process of creating aged cheddar involves placing cheese that has been put through the cheddaring process in an area where the temperature and humidity are tightly controlled. When the cheese originated in the English town of Cheddar, nearby caves provided perfect conditions for aging the cheese. The production of cheddar is now performed in many parts of the world, and the conditions present inside the caves in Cheddar are replicated so the cheese can age properly.
Most countries, including the United States, have no official guidelines about how long cheddar cheese must age to earn designations such as "sharp" or "reserve". To meet guidelines defining the chemical composition of the cheese, aged cheddar must mature for at least three months; beyond that, the taste and age of the cheddar is entirely up to the labeling and preferences of the cheesemakers. That said, extra sharp cheddar is generally aged for at least 18 months, with some commercial cheeses sitting for up to five years.
With the advent of the commercial production of cheddar cheese, some confusion has emerged as to what is actually cheddar cheese and what is not. Aged cheddar cheese is most often labeled as such and appears in blocks, sometimes encased in wax or other wrappers. Commercial cheeses that emulate aged cheddar, but are not aged, tend to be rubbery or come in the form of spreads, slices or non-solid emulsions. These cheeses are not cheddar and frequently are just flavorings suspended in oil.
Real aged cheddar has a distinct, sharp flavor and sweetness. It is best served at room temperature or only slightly chilled and eaten raw with slices of bread, crackers or fruits. The longer the cheese is aged, the less prone it is to melting smoothly and is best cooked as part of a mixture of cheeses that melt more smoothly.