Coffee brewing apparatus are classified into automatic drip coffee makers and espresso makers according to the means of delivering hot water to and through coffee grounds. Automatic drip coffee makers use the bubble power of boiling water to force little spurts of hot water up a tube and over the top of coffee grounds and the hot water subsequently seeps down through the coffee grounds by gravity. The seeping of hot water by gravity is usually so slow that the coffee may require warming before drinking, especially when a paper filter is used. For that reason, most automatic drip coffee makers have external warming plates. However, as well-known in the art, external warming may deteriorate the flavor and aroma of the brewed coffee.
The slow seeping process also indicates long contact time between water and coffee grounds, which causes more unpleasant chemicals in the coffee grounds to be extracted out into water. Besides, in order to have a reasonable seeping or brewing rate automatic drip coffee makers have to utilize fairly coarse coffee grounds, which causes insufficient extraction of the flavorings in coffee grounds and underutilization and waste of the grounds (U.S. Pat. No. 50276). Furthermore, since the bubbles (i.e. bubbles of steam at or near atmosphere pressure) which deliver the little spurts of hot water over the top of coffee grounds get into contact with the coffee grounds and are then released into atmosphere, certain important aromatic oils may be carried away by the steam from the coffee into atmosphere during the brewing process. Finally, it is well-known in the coffee trade that the quality of coffee diminishes with diminishing brewer size, which may be caused by the relatively greater proportion of filter paper surface to coffee grounds in smaller brewers.
In espresso makers, water is brought into boiling in a reservoir and then delivered under the pressure of steam trapped in the reservoir to and through coffee grounds. During the brewing process, the whole espresso maker including the reservoir is under steam pressure. Thus, the risk of steam pressure hazard is high (U.S. Pat. No. 4,741,260). Also, since the reservoir is under pressure, it can not be refilled during the brewing process. Moreover, one has to be patient to brew espresso since the brewing process will not start until the whole reservoir of water is heated to boiling. A passive solution to the problems mentioned above about espresso makers is to use a mechanical pump to deliver the hot water rather than to use steam pressure. The mechanical pump, however, makes the espresso makers more complicated and expensive.
The present invention provides a coffee brewing apparatus having novel and improved means to deliver water to and through coffee grounds, and is aimed at solving the problems associated with the automatic drip coffee makers and espresso makers.