CA1209882A - Low hot water volume warewasher - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A rack-type high capacity warewashing machine is designed to cleanse and sanitize foodware in a cycle time of the order of one minute and to accomplish sanitizing by heating the foodware with fresh hot water sufficiently to kill residual bacteria thereon. The method of operation of the machine includes a final rinse period in which fresh water at a temperature of at least 180°F (82.22°C) is sprayed over the foodware to remove residual soil and to heat the foodware surfaces to at least 160°F (71.11°C), followed by a dwell period in which the wet heated foodware is maintained in a substantially closed humid atmosphere to prolong the time during which the foodware surfaces remain above bacteria killing temperature and to cause a build-up of Heat Unit Equivalents to at least 3600.

Description

~F~N 7072 LOW IIOT WATER VOLUME WAREWASHER

B~CKGROUND OF THE INVENTION
~arewasher machines fall into two gener-ally distinct but somewhat overlapping categories, namely, commercial (restaurant, institutional or other public facility) warewashers and domestic (home) warewashers.
The cleaning efficacy and sanitization results of domestic warewashers are left to the manufacturers of such products. Most of such warewashers are designed to perform washing with an input water temperature o 1400Fo This is the basic temperature at which domestic ware~ash-ing detergents are formulated to perform mosteffectively. The warewashers are filled with clean water and drained between three and six times for each wash cycle, depending on whether the load of dishes is lightly or heavily soiled.
The operator may select any of the several differ-ent cycles he or she may wish to use. One or two of those fills will normally have detergent added to assist in stripping the soil from the dishes by means o a relatively high velocity rotating spray of pumped wash solution recirculated from a sump at the bottom of the warewasher. After washing, rinsing is accomplished by filling the sump with fresh water, recirculating it, draining the wa-ter, refilling the sump one or two additional times and repeating the rinsing operation. Such warewashers have relatively long time cycles te.g. 50 to 70 minutes) and are used once a day on the average.

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~F&N 7072 -2-Beca~se domestic warewashers are used by consumers primarily for their own families, the competitive marketplace provides the necessary in-centive to manufacturers to desi~n and build ma-chines which do an effective job of washing andsanitizing.
Commercial warewashing is an entirely different matter. It involves highly productive machines which have fixed, short washing and rins-ing cycles, measured in seconds rather than min-utes. The end responsibility for washing dishes commercially is left to a businessman dealing with members of the public whose health may be at stake when using dishes washed under that businessman's control. Because of this, there came into exist-ence in the late 1940's an organization called the National Sanitation Foundation ~N.S.F.). One of its functions is to provide minimum standards to assure that dishware washed in commercial ware-washers is in fact sanitized through bactericidal~reatment considered by health authorities to be effective. This is achieved essentially in two different ways accordilg to N.S.F. standards~
by high temperature machines which utilize a final rinse minimum time and volume and minimum tempera-ture of 180F to assure thermal death of bac-teria, or (2) by so called low temperature ma-chines which rinse with water at a minimum temper-ature of 120F, inade~ua~e to sanitize by itself, but which contains an effective germicidal chemical such as sodium hypochlorite (NaOCl). The chemical sanitizing additive must be proportioned in the rinse water at a minimum o~ 50 parts per million of availahle chlorine. Available chlorine can be defined as chlorine available to sanitize.

~F&N 7072 -3-~ ny proportion less, or anything less than 180F final rinse water in a high tempera-ture machine, is regarded by N.S.F. as not provid-ing a proper safety margin for sanitization. In high temperature machines, N.S.F. has scientifi-cally established a cumulative heat factor for a total or complete wash and rinse cycle. The heat factor is measured in "heat unit e~uivalents"
(HUE, later defined) per second of time, which, cumulated, must reach a minimum total of 3600 HUE
to be considered effective.
While N.S.F. standards are theoretically voluntary, public health and sanitation officials in the U.S. are believed to rely heavily on them.
A manufacturer is permitted to place an N.S.F.
label on the e~uipment to show that its design, manufacture and operation meet all o~ the minimum N.S.F. standards for that particular type of e~uipment. Many sanitation officials will not permit installation or use of commercial ware-washers within their jurisdiction unless they have N.S.F. labels, indicating that they are 'llisted"
as being recognized by N~S.F. In effect, N.S.F.
standards are so well accepted ~hat very few com-mercial warewashers are sold in the U.S withoutN.S.F. listingO
In both the domestic and commercial ware-washer field it has become fairly well recognized since the advent of the so-called 'lenergy crisis"
of the mid 1970's that an important way to reduce the cost and consumption of energy would be to decrease the volume of hot water used to wash dishes. For several years, domestic warewasher manufacturers have been working diligently to reduce water consumption to a mini~um which would BF&N 7072 -~-still provide satisfactory warewashing in terms of cleanliness in order to remain competitive. It can he said that, in the domestic warewasher ield, it has been and continues to be convention-al practice to seek to reduce energy consumptionby decreasing the use of hot water.
Reducing energy consumption and cost in a commercial warewasher is ~uite another matter, particularly in view of the minimum standards es-tablished by N.S.F. A variety of different typesof commercial units exists. In machines using the hot water sanitization principle, the N~S~Fo standard minimum temperature is 180F for the final rinse water, as noted. In addi~ion minimum water volumes are specified according to the size of dishrack handled by the machine. Since a mini-mum rinse temperature of 120F is acceptable in a chemical sanitizing low temperature machine, in terms of effective sanitization, the use of the sanitizer is e~uivalent to an energy saving of S0OF reduction in the final rinse temperature.
Offsetting the energy savings of chemical sanitiz-ing machines, however, is an increase in the cost of chemicals and also the initial and servicing cost of ~ uipment for dispensing the bleach and controlling water fill in the proper proportions for each warewasher cycle.
Faced with the problem of saving energy and its cost, and further faced with the 180F
temperature and water volume re~uirements of high temperature machines, the primary industry solu-tion in the past half do~en years or so has ~een to emphasize low temperature machines with chemi-cal additives. Sales of low temperature machines ~2~ 82 BF~N 7072 -5 have increased su~stantially in recent times, par-tially at the expense of sales of energy consuming high temperature machines. But such low tempera-ture machines are not without ~ault, unfortunate-ly. A prime disadvantage is that the lower tem-perature of the foodware items at the time of re-moval from the warewasher makes it considerably more difficu1t for them to air dry than when rinsed at 180. Greater heat in the items from a hot water sanitizing machine tends to drive off remaining moisture much faster. In some instances the foodware from a low temperature machine may have to be reused immediately, while still partly wet. Ordinarily the items shouldn't be towelled, because o the potential of defeating the saniti-zation purpose. Many public health codes strictly forbid towel drying of dishes. In some restau-rants, additional costly space and tabling in the kitchens have heen provided to allow dishes washed in low temperature machines a greater period of time for drying. Nevertheless, many low tempera-ture machines continue to be sold because of the reduction in energy costs as compared to presently existing high temperature machines~ This is true even though some low temperature machines have greater overall annual operating costs due to greater use of expensive chemicals, water and time to wash items.
Chemical sanitizing low temperature ware-washers have been known for many years. Origin-ally they ~ere intended for application where high temperatures were unacceptable, such as for a glass washer installed under a beverage bar~ For general warewashing, however, they have been more ~2~
BF&N 7072 widely used since the start of the energy crisis of the mid and late 1970's.
Earlier work on low temperature machines if exemplified by U. S. Patents 2,592,884;

2,592,885; 2,592,886; 3,044,092; 3,146,718 and

3,370,597. These attempted to utilize the devel-oped concepts of high temperature machines in con-junction with metering sodium hypochlorite direct-ly into the fresh water line used for final rins-ing. While these machines performed satisfactori-ly for short periods of time, they were not really successful, particularly in hard water situa-tions. Sodium hypochlorite tends to precipitate minerals, particularly calcium, magnesium and iron, from the fresh water at the point of intro-duction of the extremely small ~uantity of sodium hypochlorite metered into the water. This point in some instances was a tiny orifice in a venturi where the hypochlorite enters the fresh water line, and in others, it was the exit of a dosing system for hydraulically pumping the minute ~uan-tity of hypochlorite through a small orifice into the water line. Once such small orifices were affected by mineral build-up, metering became inaccurate or wa~ cut off and re~uired either re~
placement or fre~uent cleaning. It is doubted whether such systems using small orifices are in successful commercial existence in the U.S. today in low temperature warewashers.
At least as early as the 1940's, another form of chemical sanitizing low temperature ware-washer hecame known, initiall~ on a relatively small scale. It is referred to in the commercial warewasher trade as a "fill and dump" machine. It ~2g~$~3~32 BF&N 7072 -7 is of the general design and operation shown in U.S. Patent 3,903,909.
In such machines the rinse water is re-circulated through the same screen, pump, pipes and wash arms used by the dirty wash water, thus reducing cleanliness in the process. Injection of sanitizer directly into the sump of such ware-washers is typically done by peristaltic or pressure pumps.
In addition to the fill and dump machines, several manufacturers (including the assignee of the present invention~ have introduced a chemical sanitizing low temperature commercial warewasher which utilizes a fresh water rinse independent of the washing system, but mixes the fresh water and sodium hypochlorite in an auxili~
ary holding tank in their proper predetermined proportions prior to use by spraying through a rinse system dedicated solely to fresh rinse 501u-tion. This concept is shown in U.S. Patent~,14~,558.
The assignee of this invention had a research program in progress some years ago to design a fill and dump machine of the type shown ~5 in aforementioned U.S. Patent 3,~03,90g. The cleaning results observed in that program were deemed unsatisfactory, however, because the soiled wash water and the fresh rinse water were both circulated through the same pumps, strainers and piping, fre~uently resulting in soil carryover from the wash solution to the rinse ~ater and redepositing soil specks on the foodware. While such foodware items may be completely sanitized according to N~SoF~ standards and test methods, their apparent lack of cleanliness often gives BF~N 7072 -~-restaurant customers the impression that the items are unsanitary The consuming puhlic fre~uently associates soil on ware with lack of sanitation.
Thusl although chemical sanitizing ware-washers have achieved a niche in the marketplace, the drying problem has been and continues to be a concern. Obviously, drying of the type used in domestic warewashers (where perhaps only one load of dishes may be washed per day) is not at all acceptable in a commercial warewasher environment, where one load of dishes may have to be washed every minute or minute and a half during a main meal period. Even if such drying were made possi-ble, the energy cost of that drying would most likely defeat the very purpose of low temperature warewashing. Further, since N.S.F. specifies dif-fering miniml~m water volume usage for the various types and sizes of warewashers in the final rinse period of high temperature machines, and since the machines of most manufacturers already appear to ~e operating right at, or very near, those minimum water volumes, reduction in hot water volume usa~e below the N.S.F. standard has not appeared to be a feasible alternative in improvement of high tem-perature machine efficiency. In order to exhibitthe N.S.F. seal on the unit, t~e N.S.F. water volume minimum has seemingly been an untouchahle standard, and it thus appears that no one has searched for a way to modify it. Instead, the industry seems to have directed innovative efforts in other directions.
National Sanitation Foundation Standard No. 3 for Commercial Spray Type Dishwashing Machines, lncludes:

BF&N 7072 -9-Section 6Ø3 Heat Unit F~ uivalents:
Those commercial spray type warewashing machines relying on heat for sanitization shall, when installed and operated in accordance with the manufacturer's instructions, produce at least 3600 heat unit equivalents when evaluated in accordance with Appendix A "Heat Sanitization."
~ppendix A States:
HEAT SANITI ZATIO~: NSF Will use as a guide, Methods of Measuring Heat Unit E~uivalents, by J. L. Brown. This document is available from NSF, NSF
Building, Ann Arbor, Michigan 4810~
A general definition of Heat Unit E~uivalent (HUE) is the amount of heat applied to a foodware sur-face during exposure to heat within a warewasher~
and this unit of heat relates to the degree of bacterial destruction achieved. In actuality, the cumulative heat factor adopted by N.S.F~ includes a comfortable safety margin. High temperature commercial warewashers have been re~uired to pro-duce a measurahle cumulative heat factor of 3600 HUE for a complete wash and rinse cycle of the dish machine. ~IUE value is determined by first measuring the Fahrenheit temperature of a dish surface at each single second of time. For each second at 143F, or abovel a different HUE value is ohtained. The HUE value is logarithmically related to arithmetic increase in foodware surface temperature. For example, at 143F (60C), the HUE valuc is 1.0, at 153F (11.66C) HUE
value is 14.3, and at 163F (72.77C), the HUE
value is 203.9. The cumulative heat factor is BF&N 7072 -10-arrived at by adding all the temperatures for each second of a complete cycle, start to finish.
N.S.F., in specifying a given minimum volume of water at a minimum wash temperature of 150F for stationary rack machines and 160F for conveyor machines for a given minimum time period, and then doing likewise for rinsing with a minimum 180F
water, has in essence said that a cumulative heat factor or level of 3600 HUE is achieved when those minimums are met.
SUMMARY OF THE I NVENTI ON
The present invention accepts the b~sic cumulative heat factor re~uirement of 3600 HUE for sanitization, but not the main basic minimum re-~uirementO These are, for a stationary rack machine a specific volume of 0.43 gallons (1.6 liters) of rinse water at 180F (82.22) for each 100 s~uare inches (645 s~. cm.) of rack area, and for a typical conveyor machine a volume of 0.414 gallons (1.57 liters) at the 180F temper-ature for each 100 ~ uare inches (645 s~. cm.) of rack area. While it is known in high temperature machines, both domestic and commercial, that heat-ing of water is the primary contributor to high energy cost, what has not been known was that the HUE re~uirement of N.S.F. could be met with a red~ced volume of rinse water, provided some other means of achieving the cumulative HUE minimum were found~
That is what is accomplished with the invention. It has been found that a machine can use less of the 180F rinse water (approximately 33~ less in the preferred embodiment in one type BF&N 707~

of warewasherj, and still obtain the HWE re~uire-ment by maintaining the dishes within an essenti-ally enclosed chamber for a given relatively short period of time after completion of rinsing. At the shutoff point of the rinse water, less than half of the re~uired HUE may have been achieved, and the rest are accumulated during the immediate ly following static (dwell) hot humid period.
For example, in a single tank warewasher of the stationary rack type which has a hood or door, this is achieved either by providing a cycle light which indicates ~he warewasher is still ~unctioning to accumulate additional HUE after rinsing has discontinued, or alternatively by latching the door or hood until the re~uired humid static period has been completed.
In a conveyor type machine significant energy savings also are available by carefully controlling the flow rate and timing of the final fresh hot water rinse. In such machines the fresh hot water flow is controlled by a solenoid oper ated valve (or e~uivalent~ actuated in response to a rack located at the final rinse station. In accordance with the invention the rack of rinsed ware is kept within an enclosure at the discharge end of the machine for a time sufficient to achieve the HUE re~uirement, and the total flow of hot water from the rinse spray can be decreased in order to conserve energy.
The present invention thus achieves significant energy savings at relatively nominal cost in ~ uipment, at little or no sacrifice in machine productivity time and in a manner which, although simple, is ~uite unexpected, being con-trary to accepted past practices of the commercial 8~
BF&N 7072 -12 warewasher industry for high temperature ware-washers according to N.S.F. standards.
Although the hot water rinse volume is reduced below the presently re~uired minimum, tests conducted by N~S~F~ on a stationary rack machine incorporating the invention have resulted in the machine being approved for listing by N~SoF~ and labeling with their label. The 3600 HUE re~uirement has been met r although the volume of 180F water used per complete cycle has been reduced approximately one third, without sacrific-ing cleanahility or sanitization. The lower water volume also benefits the user in other cost-saving ways. Less water usage means less wash water dilution, and less dilution saves on consumption and cost of both deterge~t and rinse agent. Com-pared strictly to chemical sanitizing low tempera-ture machines, it also saves by eliminating sodium hypochlorite and the capital cost of its dispens-ing e~uipment. Furthermore, the aforementioneddishware drying problem associated with low tem-perature machines is avoided.
The object of the invention, therefore, is to pro~ide a novel method of operating a ware-washer, particularly of the high capacity racktype8 in which the final rinse period includes spraying the rack of foodware items with resh water at a temperature of at least 180F
(82022C) in sufficient amount and for suffi-cient time to remove residual soil and to heat thefoodware surfaces to at least 150F (6505C) for stationary rack machines and 160F
(71.11C) for conveyor machines followed by a dwell period in which the foodware is maintained in a closed humid atmosphere to prolong the time n~

BF&N 7072 13-during which the foodware surfaces remain above bacteria killing temperature; to provide such a method which thereby reduces the total heat re-~uired to sanitize foodware items in accordance with accepted standards; and to provide a ware-washing machine capable of performing such method.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view, partially broken away, showing a warewasher incorporating the invention;
Fig. 2 is a graph illustrating typical time/HUE/surface temperature relationships or a single tank, stationary rack machine; and Fig. 3 is a vertical cross-sectional view of a conveyor type warewasher incorporating the inventlon .
DESCRIPTION OF THE PREFERRED EMBODIM~NTS
P~eferring now to the drawingsr and parti-cularly to Fi~. 1, a semiautomatic, rack type com-mercial warewasher 10 is shown which includes awash chamber 12, entry to which is provided by doors 13 and 14 movable from a lower position to an upper position by means of a wrap around handle 15. A third door at the ront of the warewasher ser~es as an inspection door 1~ and may be lifted by means of handle 17.
A wash tank 20 located in a lower part of the warewasher is heated by means of an electric immersion heater 22. The water level is sensed by means of a float and switch assembly 25, and the water temperature is sensed by means of a thermis-tor (not shown) built into the float and switch assemhly. The wash tank 20 may also be heated by means of a gas fired burner located beneath and wash tank or hy steam.

~2t~ 2 B~&N 7072 Within the washing chamber 12 are revolv-ing lower and upper wash arms 31 and 32, and upper and lower rotary rinse spray arms 33 and 3~. The washing solution contained in the wash tank 20 is 5 pumped to the wash arms 31 and 32 through mani-folds 36 and 37 by means of a self-draining pump 35, driven by an electric motor 40. Rinse water is supplied through a connection ~1 to the rinse spray arms 33 and 34 under the control of a rinse 10 solenoid valve 42. A vacuum breaker 43 is pro~
vided on the downstream side of the rinse valve.
Excess water in the wash tank is removed by means of an overflow drain tube 45, the upper part of which serves to limit ~he level of water 15 in the wash tank. The lower part of the drain tube 45 fits within a drain assem~ly 46 at the lower part of the tank and is closed when the drain tube is in its lower-most position. The drain tube 4_ may be raised by means of handle 47 20 which rotates a cam 48 ~o lift the drain tube 45.
A door interlock may be provided to lock the doors 13 and 14 in the lowermost position during operation of the warewasher. This inter-lock includes a solenoid ~not shown) controlling a 25 pin which moves outwardly to prevent the upward movement of both doors. A sa~ety switch (not shown) is optionally included to terminate the warewasher operation if the doors are opened.
This switch may also be used to initiate the ware-30 washer cycle. The pump motor 40, the solenoidvalve ~2, the interlock solenoid (where used), the heater 22, the switch of the float assembly, and the temperature sensing thermistor are all con-nected to a suitable timer control. ~ suitable 8~:

~F&N 7072 -15-such control is disclosed in detail in U. S.
Patent No. 3,911,943.
Fig. 2 is a diagram which illustrates a typical operating cycle for cleansing one rack of soiled ~are in a machine such as shown in Fig. 1.
The wash period (40 seconds~ of the cycle is the time during which the main pump i5 energized, and li~uid from the tank is sprayed through the upper and lower arms 31 and 32. It should he noted that the ware surface temperature ~uickly rises to about 150F ~65.5C). N~S~Fo standards ~or this type o~ machine call for a wash liquid tem-perature of at least 150F. At the end o~ the wash period there is a short (4 seconds) dwell time, and then the rinse solenoid 42 is energized, opening the associated valve and allowing fresh hot water to enter the connection 41 and, throu~h the spray arms 33 and 34, spray over the ware in the rack. This operation performs two functionsO
~ The ware is rinsed of any remaining small parti-cles of soil, and any remaining cleaning solution is 1ushed from the suraces oE the ware. In additionl the fresh hot water, which is at a tem-perature o at least 180F, raises the surface temperature of the ware. As previously pointed out, the time that the rinse valve remains open is reduced (to 9 seconds), as compared to prior art machines, being suficient to heat the surfaces of the ware to a temperature of at least 160F.
The solenoid is then deenergiæed and flow of hot rinse water stops, but the rack o~ ware remains in the machine for an additional 9 seconds with the chamher closedO ~his can be accomplished either by a warning, such as a light operated by the timer, which warns the operator not to open the BF&N 7072 -16-doors until the light extinguishes, or by timer control of the interlock solenoid which actually latches the doors against openinq until the end of the dwell period.
The curves plotted on Fig. 2 illustrate the temperature at the surface of the ware in a typical operation of a single tank stationary rack machine, as well as the cumulative HUE against time in relationships which exist in typical machines in accordance with the invention. The cycle times are understood to be typical, but not limiting.
Fig. 3 illustrates a model of rack-type conveyor warewashing machine to which the present invention is also applicahle. In such machines racks of soiled foodware, shown generally at 40 and 42, are moved thro~gh the machine by a suit-able conveyor mechanism which is shown schemati-cally by the arrow 45. Either continuously or intermittently moving conveyor mechanisms are used depending upon the style, model and size of the machine. The racks of soiled ware enter the machine through a flexible curtain 48 into a scrapping cham~er 50, where sprays of liquid from noæzles 5~ a~ove and below the racks function to flush heavier soil from the foodware. The li~uid for this purpose comes from a tank 54 via a pump 55, and the level in this tank is maintained by a stand pipe 56 which overflows to drain.
The racks then proceed through the next curtain 58 into the main wash chamber 60, where the food ware is subjected to sprays of cleansing li~uid from upper and lower nozzles 62, these being supplied by a pump 65 which draws from the main tank 66. A heater, shown schematically as an BF&N 7072 -17-electrical immersion heater 67, and provided with suitahle thermostatic controls, maintains the tem-perat~re of the cleansing li~uid at a suitable temperature, as in the order of 160F. Not shown, but typically included, are a device for adding a cleansing detergent to the li~uid in the tank 66, and controls for this device which main-tain the concentration of detergent within desired limits. Overflow from tank 66 exits via pipe 68 into the scrapping li~uid tank 54. Above the over~low 68 there is a small catch pan 69 which may ~e used to direct any splash of scrapping li~uid that passes under the curtain 5% down into the overflow 68 and back to tank 54. During lS normal operation of the machine, the pumps 55 and 65 are continuously driven, usually by separate ~otors, once the machine is started and until the period of use of the machine is completed.
The racks of cleansed ware exit the main chamber 60 through a curtain 70 into the final rinse chamber 72, which is provided with upper and lower spray heads 74 that are supplied with a flow of fresh hot water via pipe 75, and under the con-trol of a solenoid operated valve 76. This water is, in accordance with NSF and similar standards~
supplied at a temperature of at least 180F.
rack detector 77 is actuated when a rack of ware is positioned in the chamber 72, and throu~h suit-able electrical controls the detector controls energizes the solenoid valve 76 to open and admit the hot rinse water to the spray heads 74. The fresh water drains from the ware into tank 66.
The rinsed racks of food ware exit cham-ber 72 through curtain 80 and, in this embodiment of the invention, enter and pass thro~gh a chamber ~l2'~

~F&N 7072 -18-defined by a hood 82 with side walls and an exit curtain 84. The length of the hood 82 is suffi-cient to define a holding chamber 85, within which the racks of hot sanitized ware are maintained in a substantially enclosed humid environment. In one successful embodiment the length of hood 82 is 20 inches (50.8 cm.). This allows the buildup of ~UE in essentially the same manner as previously described in connection with stationary rack ma-chines. Here, the dwell period is the time during~hich a rack of rinsed ware traverses chamber 85.
It should be noted that the intermediate curtain 80 is not essential, but it is part of the prefer-red embodiment.
In the conveyor type machines, the advan-tage of the invention results from a reduction in the ~uantity of fresh hot water used for each final rinse operation, while still obtaining the necessary total HUE at the surface of the ~are in order to sanitize this ware in accordance with accepted standards. ~.S.F. standards for a typi-cal such machine re~uire a cleaning solution tem-perature of at least 160F (71.1C), 10F
higher than the stationary rack machine. This of course hrings the ware to the final rinse position ~ith a slightly higher sur~ace temperature. Typi-cal prior conveyor machines have used in the order of 2.3 gallons l8.71 liters) of 180F final rinse water for each final rinse spraying. With the present invention this ~uantity can be reduced to in the order of 1.4 gallons (5.3 liters) rinse per standard rack.
While the methods herein described~ and the forms of apparatus for carrying these methods into effect, constitute preferred embodiments of ~2~

~F~N 7072 ~19-this invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either witho~t departing from the scope of the invention which is defined in the appended claims.

Claims (6)

CLAIMS:

1. In a commercial dishwasher, a complete ware-washer cycle for (1) washing food soil from successive racks of ware such as dishes and utensils with a cleaning solution of water and detergent, (2) rinsing the ware with fresh water, and (3) effectively sanitizing the ware to a cumulative heat factor level over the complete cycle to meet accepted heat sanitization practices, comprising the steps of:
(a) loading soiled ware into the racks and placing a loaded rack in a substantially enclosed wash chamber of a ware-washing machine, (b) recirculating a supply of cleaning solution in said chamber under pressure through nozzles which direct the solution over the ware in sufficient volume and at a predetermined washing temperature with sufficient velocity and for a pre-determined washing time period effective to strip the soil from and thereby wash the ware, (c) maintaining said cleaning solution supply at a minimum washing temperature during the washing time period, (d) upon completion of the washing time period, providing a short dwell period during which soiled solution can drain from the ware, then (e) sanitizing the ware by sequentially:
(i) rinsing the ware for a predetermined rinse period with fresh rinse water heated to a minimum santizing temperature greater than said washing temperature and delivered through rinse nozzles dedicated solely to said rinse water and directed toward the ware, said rinse water being delivered in a volume sufficient to rinse loose food soil and remaining cleaning solution from the ware and achieve a substantial reduction in water volume in order to conserve energy, and said rinse period being of a duration whereby the surfaces of the ware rise from the temperature achieved during washing to a higher temperature to apply heat unit equivalents per second of time to said ware between an approximate minimum of 40% but less than 100% of the cumulative heat factor level required by accepted sanitization practices to achieve sanitization, and, (ii) upon completion of the rinse period and while the ware is still exposed to the accumulated rinse water and cleaning solution, maintaining the ware within a substantially enclosed chamber for a time period, in addition to any inherent time delay of a cycle controller, sufficient to allow the heated humid atmosphere within said chamber achieved without further addition of heat except from the heated fresh rinse water to apply to the ware surfaces additional heat unit equivalents, which, coupled with those applied during prior washing and rinsing, raises the cumulative heat factor for the complete ware-washer cycle above the minimum level required to effectively sanitize the ware, and then (f) removing the clean, sanitized ware from the machine.

2. The warewasher cycle of claim 1, wherein said minimum washing temperature is 150°F. and said minimum rinsing temperature is 180°F.

3. The warewasher cycle of claim 1 wherein the rinse period duration and the minimum washing and rinsing temperatures are such as to achieve a minimum ware surface temperature of approximately 165°F. by the end of the rinse period.

4. In a commercial rack-type high capacity ware-washing machine designed to cleanse and sanitize foodware in a cycle time of the order of one minute and to accomplish sanitizing by heating the foodware with fresh hot water sufficiently to kill residual bacteria thereon, wherein racks of ware are first sprayed with a cleaning solution to strip the soil from and wash the soiled ware and then the racks are rinsed with fresh hot water, the improved method of operation including a final rinse period in which fresh water at a temperature of at least 180°F is sprayed over the foodware to remove residual soil and to heat the foodware surfaces to at least 160°F., and a dwell period, in addition to any inherent time delay of a cycle controller, following said rinse period and while the ware is still exposed to the accumulated rinse water and cleaning solution in which the wet heated foodware is maintained in a closed humid atmosphere without further addition of heat from a source other than the fresh hot water to prolong the time during which the foodware surfaces remain above bacteria killing temperature and to achieve a substantial reduction in rinse water volume in order to conserve energy.

5. In a single rack compartment type warewashing machine having a tank for holding cleaning solution, means for supporting a rack of soiled foodware items over said tank, a wash circuit including a pump and nozzles for spraying and recirculating the solution over the soiled items, a separate fresh water rinse circuit including rinse nozzles and a hot fresh water connection to said rinse nozzles adapted to receive fresh water at a temperature of at least 180°F and to spray the same over the items, and a valve controlling flow of water into said rinse circuit; the improvement comprising a cycle controller connected to operate said pump and said valve in predetermined time sequence, said controller including (a) means for operating said pump first through a wash period in which said wash circuit sprays cleaning solution over soiled foodware items and then stopping said pump so the solution is allowed to drain from the foodware items, (b) means for then opening said valve through a rinse period in which said rinse circuit sprays fresh hot water over the foodware items to remove any remaining cleaning solution and to heat the foodware items to bacteria killing temperatures, (c) means for then providing a signal indicating a dwell period during which the heat energy transferred to the foodware items is slowly dissipated to ensure effective sanitizing of the foodware items.

6. In a rack type warewashing machine having a tank for holding cleaning solution, conveyor means for supporting a rack of soiled foodware items over said tank, a wash circuit including a pump and nozzles for spraying and recirculating the solution over the soiled items, a separate fresh water rinse circuit including rinse nozzles and a hot fresh water connection to said rinse nozzles adapted to receive fresh water at a temperature of at least 180°F and to spray the same over the items, a valve controlling flow of water into said rinse circuit, a controller connected to open said valve during movement of a rack past said rinse nozzles by said conveyor means for a period of time sufficient that the surfaces of all ware in the rack are rinsed of residual soil and heated to at least 160°F, and means defining a holding chamber along said conveyor means and past said rinse nozzles to enclose the rinsed foodware items for a predetermined time after rinsing with hot water during which heat energy transferred to the foodware items from the hot water is slowly dissipated to ensure effective sanitizing of the foodware items.