Abstract:
A portable hot water dispensing machine, particularly suitable for dispensing espresso, that is compact, lightweight, requires minimal power to operate, and is readily transportable, and a method of dispensing hot water, such as espresso. Two-stage heating is utilized for reducing the boiler volume and power requirements. In addition, components are thermally insulated and are strategically spaced to maximize space and allow for portability.

Description:
This application claims priority from Provisional Application Ser. No. 60/630,931 filed Nov. 24, 2004, the disclosure of which is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   The popularity of coffee and espresso drinks has grown recently, and in-home espresso machines are becoming more and more commonplace. These drinks conventionally have been prepared by brewing, where hot water passes through coffee grounds above a filter, under pressure in the case of espresso machines. Indeed, a defining characteristic of electrical espresso machines is that the coffee grinds are infused with hot water under a substantially constant high pressure supplied by an electrical pump. The hot water pressure is usually more than 100 psi throughout the infusion/extraction cycle. 
   Conventional electrical espresso machines contain the following major components in sequence: a cold water reservoir or direct connection to external cold water supply; a cold water pump; a boiler or thermo-block; a group/brew head; and a portafilter. These components are usually arranged in side-by-side relation. The machines operate as follows. The boiler is filled with water and preheated to a temperature greater than 180° F. prior to activating the pump. During the brewing process, the pump pressurizes the cold water from the water reservoir and injects it into the hot boiler. The pressure from the incoming water forces the hot water already in the boiler into the group or brew head. The hot water than infuses the coffee in the portafilter, and exits into a cup or other receptacle placed under the portafilter. 
   Typically, espresso machines for home use are larger than about 14 inches high, 10 inches long and 8 inches deep, weigh more than twenty pounds, and require more than 1 kW power to operate. The minimum size and weight of known espresso machines are in part limited by the process sequence described above. For instance, the water is completely unheated before entering the pump, and is heated to the espresso temperature in a single step by the boiler or thermo-block. This requires a large volume of heated water in the boiler, and thus a powerful heater is necessary. Indeed, the water must be heated to about 205° F. in about 20 seconds, which is the optimum brewing time for espresso. Also, for temperature stability, the volume of the boiler is typically at least four times the volume of the prepared coffee, and components such as the boiler, group, and portafilter are typically made of heavy cast brass. 
   In view of their weight and form, known espresso machines are difficult to transport. Moreover, they cannot be used in passenger vehicles or easily packed for a trip. To be portable, an espresso machine should be lightweight, compact, devoid of protruding parts and should not occupy a large volume. They should be sufficiently sturdy to withstand rough handling. Furthermore, to be usable in a passenger vehicle, an espresso machine should have all of the above characteristics but also should require no more power than that available through a typical vehicle&#39;s power outlet, typically 120 W continuous. The machine also should be spill-proof. 
   SUMMARY OF THE INVENTION 
   The problems of the prior art have been overcome by the present invention, which provides a portable hot water dispensing machine, particularly suitable for dispensing espresso, that is compact, lightweight, requires minimal power to operate, and is readily transportable. Also provided is a method of dispensing hot water, as well as espresso. 
   In certain embodiments of the instant machine, two-stage heating is utilized for reducing the boiler volume and power requirements. In addition, components are thermally insulated and are strategically spaced to maximize space and allow for portability. In certain embodiments, the machine can be disassembled in two or more pieces for convenient storage and transportation. The machine also can be used to dispense hot water for beverages other than espresso, such as hot tea or hot chocolate. Preferably the major dimension of the apparatus does not exceed fourteen inches, and preferably the apparatus weighs about ten pounds or less. The required continuous power for operation of the electrical components of the machine preferably does not exceed about 120 W. 

   
     BRIEF DESCRITION OF THE DRAWINGS 
       FIG. 1  is a an exploded view of a portable espresso machine in accordance with the present invention; 
       FIG. 2  is a cross-sectional view of an alternate water heater that can be used in the machine of the present invention; and 
       FIG. 3  is a cross-sectional view of a suitable thermo-block that can be used in the machine of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Turning first to  FIG. 1 , a vertically stacked espresso machine in accordance with the present invention is shown in an exploded view. Although an espresso machine is illustrated, those skilled in the art will appreciate that the machine can be used to produce hot water for other beverages, such as tea. 
   The machine includes a reservoir  1  having an open top that is enclosed with a suitable cover  2  that can be secured to the reservoir  1  to close the open top by any suitable means, such as by screwing, latching or with a snap-on fit. Preferably the cover  2  is breathable to prevent pressure from forming during heat-up, and to prevent a vacuum from forming in the reservoir  1  during the pumping operation. The breathable characteristics of the cover  2  can be achieved with a suitable check valve (such as a nylon check valve commercially available from United Plastics Corporation) or membrane, as is known by those skilled in the art. The check valve can be a pressure-relief valve  23  with a differential break pressure of about 1 psi, and/or a vacuum relief check valve also with a differential break pressure of about 1 psi. The check valve can be threaded into the cover  2 . Preferably the reservoir  1  is thermally insulated with suitable insulation  3  as shown, and holds a volume sufficient to provide at least one typical espresso drink (about 50 ml) but no more than about 2 typical espresso drinks (about 100 ml). 
   Positioned in the reservoir  1  is a heater  4  for first-stage heating. The type of heater is not particularly limited, and includes electric heaters capable of generating 100 W, such as the 100 W tubular immersion heaters commercially available from Watlow Electric. Those skilled in the art will appreciate that other suitable heaters can be used, such as conduction heaters, provided they are capable of high temperatures but do not exceed temperature above about 180° F. (which can be due to over-temperature thermostat control). The immersion heater  4  includes a sealed electrical connection  4 A. Spaced from reservoir  1  and preferably positioned vertically under the reservoir  1  is electrical compartment  6 . The compartment  6  includes pump  7 , preferably an electric high-pressure pump (piston type) for supplying a suitable steady water pressure sufficient for making espresso, such as a pressure of about 100 psi or higher. The exterior wall of the machine may have perforations or the like (not shown) in the area of the pump  7  in order to provide cooling of the high-pressure pump. A switching thermostat  5  is attached in intimate contact with the bottom of the electrical reservoir  1  to sense the temperature of the water in the reservoir. Suitable thermostats include snap-disk bimetallic thermostats, or a contact or immersion thermocouple in combination with a temperature control. A suitable on/off temperature point for the thermostat  5  is about 140° F. ±15°. Electrical controls and signal LED&#39;s  22  may be provided in compartment  6 . Preferably the reservoir  1  and electrical compartment  6  can be assembled to form an integral modular unit. 
   Spaced from the compartment  6 , preferably vertically, is a pressure-tight thermo-block  8  having a built-in heater  9 . Preferably the thermo-block  8  has a water channel  26  ( FIG. 3 ) that spirals, with the heater  9  also provided in a spiral configuration juxtaposed to the spiraling water channel  26 . This arrangement is thermally insulated from the outer wall housing the thermo-block with suitable insulation  11 , and provides conductive heating of the pressurized pre-heated water (second-stage heating). Preferably the thermo-block  8  is made of a food-grade aluminum alloy. Switching thermostat  10 , attached to the top of the thermo-block (and including apportion housed in chamber  6  as shown), senses the temperature of the thermo-block. A suitable on/off temperature for the thermostat  10  is about 210° F. ±15° (the 15 differential reflecting the hysteresis typical of snap disk thermostats). A group or brew head  12  distributes hot pressurized water above the portafilter  13 . Preferably the brew head  12  incorporates a water diffuser (shower) plate, and sealing ring  27  for sealing against the portafilter basket  14  discussed below. 
   Not shown are two over-temperature thermostats, similar to thermostats  5  and  10  but preset to higher temperatures, that provide over-temperature protection to the water reservoir and the thermo-block. 
     FIG. 2  illustrates an alternative to the thermo-block  8 . Thus, a sealed oil-filled heater can be used in order to further reduce the weight and volume of the machine. Prior to activating the pump, the oil  19  in the sealed heater is heated by the heater coil  20  to a temperature higher than the required espresso temperature. The pump then pumps the pre-heated water from the water reservoir into the copper tubing  21 , where the pressurized water therein is heated conductively to the required temperature using the heat energy stored in the oil. Oil  19  has higher heat capacity (Cp) than aluminum, therefore it can store more heat energy and, if heated by the immersion heater  20  before activating the pump  7 , it can heat up the water passing through the coiled line  21  more efficiently and quickly, with a better water temperature control, and with less additional energy than are required of the thermo-block  8 . 
   A portafilter basket  14  sits in the portafilter  13  and holds the beverage material from which flavor is to be extracted such as by brewing, such as ground coffee in the form of loose tampered grinds, pods  15  or capsules; tea leaves which can be ground; beverage powders such as cocoa powder; etc. The basket  14  can be pressurized (as shown) or non-pressurized. Preferably the basket  14  includes a crema nozzle  16  as shown. The nozzle  16  can be permanent or changeable for use with the pressurized basket. Different nozzles may be used with different coffee types, containers, and grind size in order to produce optimum results, which generally requires an infusion time (the time during which the pressurized hot water and the coffee grinds are in contact with each other) of 20-25 seconds. The portafilter  13  can be frusto-conical in shape, and includes an optional nozzle or spigot  17  for the dispensing of the liquid beverage into a suitable receptacle  18  such as a coffee cup without splashing and loss of crema. It is preferably located vertically below the thermo-block  8  and brew head  12 , which in turn is preferably positioned vertically below the electrical chamber  6 . 
   Alternatively, in order to reduce the number of components, the basket function can be integrated within the portafilter. Also, the crema nozzle, if present, may be assembled to or integrated within the portafilter. When there is no power restriction, the thermo-block heater  8  can be powerful enough to raise the water temperature to above 250° F. and produce steam such as for milk-based espresso drinks. 
   Preferably the heaters, pump, brew head and portafilter are arranged in one or more housings with perimeters that are vertically aligned in order to provide a compact machine. The machine can be modular, and thus disassembled in two or more locations and quickly reassembled prior to use. Preferably the outer housings are made of a lightweight material, such as plastic or aluminum. 
   In operation, the beverage material such as coffee is placed in the portafilter basket  14 . Ground coffee may be placed directly in the basket  14 , or a prepackaged coffee pod  15  or a coffee capsule may be used, for example. Cold water is introduced into the reservoir  1  through the open top, and cover  2  is used to close the top of reservoir  1 . The water in the reservoir  1  is then preheated by the heater  4  to a suitable temperature compatible with the inlet temperature of the pump  7 , but preferably not exceeding 150° F., in order to prevent hot-water scalding and excessive steam buildup. A suitable temperature range is from about 130° F. to about 150° F., most preferably about 140° F. 
   Where power is not a restriction, the thermo-block  8  may be preheated simultaneously with the heating of the water in reservoir  1 . Once the water preheat temperature has been reached as sensed by the thermostat  5 , the brew process is activated, such as by a user-operated switch (not shown) or automatically in response to the sensed temperature. The heater  4  can be turned off, and the pump  7  activated to pump water into the pre-heated thermo-block  8 . Where power is restricted (such as in vehicle-portable machines), the thermo-block  8  may be heated prior to, or after, preheating the cold water in the reservoir  1  but before activating pump  7 . Similarly, depending on the power restriction, the thermo-block heater  9  can be left on during the brew process, or can be turned off after preheating the thermo-block  8  and before the pump  7  has been turned on. 
   In the embodiment of  FIG. 1 , the pre-heated water from the reservoir  1  enters the pre-heated thermo-block  8 , preferably near the perimeter in order to maintain the outside wall temperature relatively low, and spirals toward the center of the thermo-block. The water is heated to a suitable temperature by the thermo-block  8 , preferably in the range of about 190° F. to about 220° F., most preferably about 205° F., before entering the group or brew head  12 . In order to minimize or prevent the temperature of the water from falling upon entering the group or brew head  12 , the group or brew head  12  may be part of, or in intimate thermal contact with, the thermo-block  8  to allow for conductive heat transfer and temperature uniformity. The group or brew head  12  preferably holds the portafilter  13  and basket  14  and distributes the hot pressurized water over the beverage material for extraction. Optimum brewing time is from about 20 to about 25 seconds, and optimum infusion temperature (the temperature at which the water makes contact with the beverage material) is about 205° F. The resulting beverage, such as espresso, flows through the portafilter spout  17  and into a suitable receptacle, such as a spill-proof insulated cup  18  that is removably attached to the machine. 
   For optimum espresso quality over a range of coffee types and grind sizes, as well as for preparation of a wide variety of other hot drinks, the basket  14  may be pressurized by means of a removable cream nozzle  16  having an opening with a fixed or variable cross-section to accommodate various sized beverage materials such as coffee grinds. 
   In the event the machine is used for beverages other than espresso, suitable flavoring or other material (such as tea leaves) is placed in the portafilter. If the machine is used simply to dispense hot water, the portafilter can be left empty, or the brew head and/or portafilter can be completely removed from the apparatus.