Manual of Naval Preventive Medicine
Chapter 1: Food Service Sanitation
Section II: Standards and Sanitation of Food Service Equipment and Utensils

1-9. Dishwashing Methods.

Department of the Navy
Bureau of Medicine and Surgery

1. Introduction

a. Thoroughly cleaned and sanitized food service dishware, utensils and equipment not only contribute to the aesthetic quality of a food service facility, but more importantly, prevent the transmission of disease-producing microorganisms that may be found on such utensils and equipment. Therefore, the importance of thorough cleaning and sanitizing cannot be overemphasized.

b. Utensils and equipment including removable equipment components may be washed by the manual or machine method; however, when available the machine dishwashing method is preferred. Whichever method is used, the final results will depend on the supervision, knowledge, skill, and conscientiousness of the personnel doing the dishwashing and the equipment and materials provided for their use. All dishwashing personnel and their supervisors must be alert to the hazards associated with so-called "short cuts" and slipshod procedures for dishwashing and sanitizing.

c. A sufficient supply of dining gear must be available to prevent the recycling of inadequately cleaned, wet or hot dishware and utensils.

d. Care will be taken to prevent contamination of clean and sanitized dishware and utensils by eliminating the cross handling of soiled and clean items and protecting the clean items from splashes or aerosols. Dishwashing areas must be designed and equipment placed so that the direction of flow of dishware and utensils is from the soiled areas (scrapping and preflushing) to clean areas (drying area) to minimize the possibility of contamination from the soiled articles. Multiple rack dishwashers must be installed so that the intake/discharge ends of the machine are oriented fore and aft aboard ships. This is to prevent cross contamination of rinse water with wash water by the ships' roll characteristics.

e. Adequate sanitary storage space will be provided to protect the cleaned and sanitized dishware and utensils from contamination resulting from unnecessary handling, dust and splashes.

f. Correct and approved procedures will be discussed in the following paragraphs. Additional information is contained in the NSTM 9340, 0901-LP-332-002; Food Service Operations, NAVSUP PUB 421; Standardization Handbook Dishwashing Operations, Military Handbook (MIL-HDBK) 740; and Enlisted Dining Facility Master at Arms Handbook, NAVSUP PUB 520.

2. Manual Dishwashing

a. Equipment

(1) A three compartment deep sink is basic for proper manual dishwashing procedures. If a three compartment sink cannot be provided, a two compartment sink and/or other containers, e.g., large kettle, etc., may be used provided adequate provisions are made to accomplish the basic manual dishwashing procedures including scraping and preflushing, washing, rinsing and sanitizing.

(2) Accessory equipment and supplies required for proper manual dishwashing include a booster heater for the final rinse sink; thermometers for monitoring the final rinse water temperatures, a drip and drain basket for the final rinse, approved brushes, hand dishwashing compounds, and sanitizing agents. In addition adequate facilities are required for scraping and prefiushing, stacking soiled dishware and utensils, and air drying cleaned and sanitized items.

b. Procedures. Manual dishwashing entails four separate evolutions including scraping and preflushing to remove gross soil, washing in detergent and warm water to remove soil and grease, rinsing to remove residual detergent and grease, and sanitizing to eliminate pathogens.

(1) Scraping and Preflushing

(a) Scraping and preflushing is accomplished to remove residual food matter which would pose an excessive organic load on the wash water and detergent. Gross food and trash are removed with a rubber spatula, approved brush or gloved hand, and deposited in a garbage receptacle. The surfaces of the dishware and utensils are then flushed with warm water (about 110 degrees F to 120 degrees F) to remove excess soil and grease. This can be accomplished in a warewashing machine with a prewash cycle, under a running faucet or in a deep sink.

If the latter method is used, the sink must be emptied and cleaned prior to its use for washing or rinsing.

(b) Flatware (knives, forks and spoons) should be soaked in warm water (120 degrees F to 125 degrees F) containing 3 ounces of hand dishwashing compound per gallon of water as soon as possible after they are collected. When the presoak water becomes dirty or greasy it should be changed.

(c) Experience has shown that the capacity of the wash water to clean dishware and utensils increases significantly when thorough scraping and preflushing is accomplished.

(d) Damaged flatware should be segregated for proper disposal at this point.

(2) Washing

(a) Manual dishwashing is accomplished in a clean deep sink or other suitable container which is filled with warm water maintained at a temperature of 95 degrees F-125 degrees F, or the temperature specified on the label of the hand washing detergent or other cleaning agent. The cleaning agent is added according to the label. The amount of water in the sink or container must be known in order to mix the correct concentration. Dishware and utensils should be individually hand washed with an approved scouring pad or other suitable implement. The wash water should be changed when it becomes dirty. This will be evident by a lack of suds or the presence of a thin grease film on the water's surface.

(b) Glassware should be washed first using approved glassware brushes followed by flatware, dishes, and pots and pans, in that order, to minimize the frequency of water changes during the dishwashing operation.

(c) Pots and pans should be washed thoroughly inside and out by means of a scrub or scouring pad. Burnt food and difficult to remove stains can be removed by using a small amount of scouring powder and rubbing in a circular motion until the stain is removed.

(3) Rinse. The purpose of the rinse is to remove cleaning agents and food residues with potable water and prevent carryover into the sanitizing rinse. It is accomplished in the second deep sink which contains clean warm water (120 degrees F to 140 degrees F is generally recommended). Some detergent-sanitizers are used in both the wash water and the rinse water, check the label and mix as directed. The rinse water or detergent-sanitizer solution should be changed when suds and/or grease begin to accumulate on the surface.

(4) Sanitizing Rinse. Dishware and utensils are sanitized in the third deep sink or other container by immersion for at least 30 seconds in clean hot water at a temperature of at least 170 degrees F, or for at least 1 minute in an approved chemical sanitizing solution such as the standard stock chlorine-iodine type. When chlorine chemical sanitizers are used, the immersion time may be reduced to at least 10 seconds provided one of the following combinations of pH, water temperature and concentration of free available chlorine (FAC) is used. See Table 1-1 below.

(5) Drying and Storage. Dishware, glassware, pots, pans, and utensils must be air dried and stored in a manner which protects them against contamination.

(6) Maintenance. The dishwashing area and equipment must be kept in good repair and cleaned before the operator leaves the area.

Table 1.1 Methods to Reduce Chlorine Sanitizing Rinse Time to 10 Seconds

Minimum Temperature	Chlorine Concentration
Degrees F	pH 8.0 or less	pH 8.1-10.0
120	23 ppm	25 ppm
100	50 ppm	50 ppm
75	50 ppm	100 ppm
55	100 ppm	100 ppm

3. Machine Dishwashing

a. Equipment

(1) Sanitary standards for dishwashing machines must not be less than those promulgated by NSF. Equivalent to NSF will be interpreted and understood to mean equivalent in all respects, including: comprehensive evaluation and testing of products by qualified professionals, unannounced inspections of production facilities, periodic re-evaluation of products, uniform interpretation of the standard, continuing objective evaluation against new revisions of the standard, enforcement procedures to assure against misuse of a listing or registered mark, free published listing of accepted products, field investigation procedure available on request, and a formal appeals process for evaluation to the standard or enforcement procedures. More extensive information may be obtained from the current NSF Standard NO. 3, Commercial Spray Type Dishwashing Machines. NSF approved thermometers on the dishwashing machines will be maintained in good operating condition at all times and must be verified to ensure accuracy by preventive maintenance personnel during routine servicing and whenever a thermometer malfunction is suspected but not less than once per month. The sensing element of the final rinse thermometer must be located to indicate the temperature of the water at the spray arms or manifolds. Each temperature gauge must be clearly marked to indicate the required temperature range. The low temperature shut-off switch that prevents the machine from running when proper water temperatures are not obtained must not be bypassed to allow the machine to run. Steam injection for heating dishwater in dishwashers deep sinks and serving lines is prohibited.

(2) Dishwashing machines are classified as single or multiple tanks and stationary rack or conveyor type. They are designed to remove physical soil from all surfaces of dishware or utensils and sanitize them either by the application of hot water or by the application of approved chemical solutions to the surfaces of the dishes or utensils. Operating specifications for each type of machine are listed in Table 1-2.

(3) The effectiveness of dishwashing machines is dependent on several factors:

(a) Scraping and Prewashing. These operations are very important because they reduce the organic load on the dishwashing machine, thus increasing its efficiency. Scraping and prewashing also remove large portions of soil and grease which result in more efficient machine operation.

(b) Racking. The proper placement of dishware and utensils in the dishwasher assures that all the surfaces will be exposed to the spray jets of wash and rinse water.

(c) Timing. Each stage of the dishwashing cycle is timed to provide the optimum exposure required to remove physical soil and sanitize the dishware and utensils.

(d) Volume and Velocity of the Water. The volume and velocity of the wash and rinse water affect the degree of soil removal by providing the necessary force to remove soil from the dishware and utensil surfaces and carry it away. Therefore; it is important that the spray arms and nozzles be kept free of obstruction to ensure dishware and utensils are exposed to the proper washing and rinsing action.

(e) Temperature of Water. In general, an increase in temperature of the wash water up to 150 degrees F aids in the removal of soil by decreasing the strength of the bond between the soil and the dishware surfaces increasing the solubility of the soil, and increasing the reaction rates. In addition, the cumulative effect of the temperatures of the wash and rinse cycles are necessary to obtain a minimum temperature of 161 degrees F on the surface of the utensil to assure sanitization. Water temperatures less than those prescribed in Table 1-2 for wash or rinse water will result in ineffective washing and sanitizing.

(f) Dishwashing Agents. Dishwashing agents (detergents) facilitate soil removal by attacking the water insoluble matter which occurs on dishware and utensils, such as mineral deposits, animal and vegetable fats, and fibrous matter. In order for the cleaning agent to be effective, it must be compatible with the chemistry of the wash water, e.g., hard or soft water. Dishwashing agents are discussed in more detail in Article 1-10.

b. Procedures

(1) Scraping and Preflushing. Dishware and utensils must be scraped and preflushed as describe,d in Article 1-9.2.b.(1). Some machines are equipped with an automatic preflushing function. In this event the dishware and utensils still require manual scraping before being placed into the machine.

(2) Sorting and Racking. Dishware and utensils should be sorted according to size and shape prior to racking. Separate racks must be used for articles of different types, e.g., cups, plates, bowls, and glasses will not be placed in the same racks. Similarly, like items must be placed together on reckless conveyor type machines. Items must be racked in a manner that allows the surfaces to be exposed to the water spray and permits complete draining, overcrowding and haphazard racking must be avoided. Flatware will be individually scrubbed with a brush after presoaking to remove remaining food residues and placed in separate cylindrical shaped containers according to type, e.g., forks with forks, etc., with the eating surfaces facing up.

*Pressure not less than 15 psi, not more than 25 psi, **Temp. at the manifold

(3) Machine Operation. The dishwashing machine should be operated in accordance with the manufacturer's instructions. Care should be taken to ensure that the proper amount of appropriate dishwashing compound and rinse additives are used, the spray nozzles are not clogged, prescribed water temperatures and pressures are maintained, and the final rinse mechanism is operating satisfactorily.

(4) Drying and Storage

(a) When dishware and utensils are washed and rinsed at the prescribed temperatures, and with proper use of machine dishwashing compound and drying agents, the drying time of properly racked items in an adequately ventilated room is a few minutes.

(b) A sufficiently large clean table area and adequate number of racks will be provided to permit sufficient holding time to allow the dishware and utensils to air dry before they are unloaded. The racks should be shaken to dislodge entrapped water and facilitate complete drying. The use of towels for drying dishware and utensils is prohibited.

(c) The dishware and utensils must be inspected at this point for cleanliness and the presence of residual detergent or grease films. Inadequately cleaned or filmy items will be rewashed and the cause of the occurrence investigated. Proper illumination in the space where dishware and utensils are air dried and inspected is of the utmost importance and must meet or exceed applicable illumination requirements.

(d) Care must be taken to avoid handling the food-contact surfaces of dishware and utensils once they have been cleaned and sanitized.

(e) All dining gear and cooking utensils must be stored off the deck and will be protected against contamination from dust, splashes, aerosols, and handling. Storage of dishware and utensils is prohibited in sculleries which have approved salt water garbage grinders (unless a separating deck to overhead partition is provided to isolate clean gear), locker rooms, toilet rooms, toilet room vestibules, garbage rooms, mechanical rooms, leaking automatic fire sprinkler heads, under exposed sewer lines, leaking water lines, or lines on which water has condensed.

(5) Maintenance. The dishwashing machine will be cleaned thoroughly at the end of each meal period following the instructions in the operating manual. Disassembly of spray arms, removal of scrap trays and spray curtains and a thorough cleaning inside and out after each period of use helps ensure that the machine will operate effectively at all times. The dish carts drain boards, braces, sinks, and brushes will also be cleaned thoroughly. The dish tables (and conveyers) will be cleaned using detergent and brushes and rinsed with fresh water. The tables (and conveyers) will be wiped with a sanitizing solution. The shelves, legs, deck drains, decks, and bulkheads must be cleaned daily to avoid accumulation of grease, slime and food particles. Before the operator leaves the area, all equipment must be clean and ready for the next operation.

(6) Inspection of Dishwashing Machines. The task of determining whether a dishwashing machine is effectively washing and sanitizing utensils is an involved process, particularly without sophisticated laboratory instrumentation; however, it can be satisfactorily accomplished by the procedures outlined below:

(a) Determine that the dishes are visibly clean;

(b) Establish if personnel operating the machine are adequately trained and are performing their functions correctly including scraping, preflushing, racking, and sorting;

(c) Determine if the proper dishwashing compound and drying agents are being correctly used and that adequate supplies are available;

(d) Use a calibrated thermometer (bimetallic, maximum registering, pyrometer, etc.) to determine the temperatures of the wash water and power rinse water (when appropriate) by immersion in the water contained in the respective tank(s). The water should be within the temperature ranges given in Table 1-2. If the machine temperature gauges do not agree with the calibrated thermometer within + 3 degrees F the gauges must be calibrated or replaced. As a temporary measure, the corrective differential (i.e., the difference between the calibrated thermometer and the machine gauge) should be displayed on or near the temperature gauge in error until the machine gauge is repaired;

(e) The final rinse temperature is more difficult to determine since it is based on the temperature of the water at the final rinse manifold. The final rinse temperature can be ascertained by one of the following procedures:

1) Remove the final rinse thermometer or sensing unit from the inlet manifold. Compare the machine thermometer or sensing bulb with a calibrated thermometer by immersing both in a container of hot water (180 degrees F to 195 degrees F). If the machine gauge is in error by more than + 3 degrees F, it must be calibrated or replaced and the corrective differential temporarily posted. With this information, the final rinse temperature can be determined by observing the machine gauge while the machine is operating; or

2) Place a calibrated thermometer directly under the final rinse spray to measure the water just as it leaves the spray nozzle. This can be accomplished by attaching a calibrated thermometer with rubber bands to an extension device such as a broom handle and placing the thermometer directly under the spray nozzle while it is operating. This may not be possible on single tank stationary rack machines unless a pyrometer is used. Caution! Care must be exercised in order to prevent injury! A maximum registering thermometer or a pyrometer are the best instruments to use for this procedure; however, other calibrated thermometers may used. The temperature of the final rinse spray at the spray nozzle, except for single tank stationary rack single temperature and chemical sanitizing machines, must be at least 180 degrees F;

3) An indirect method of assuring the final rinse temperature is at or above 180 degrees F is to pass temperature sensitive tape which indicates 170 degrees F or a maximum registering thermometer through a complete wash and rinse cycle. The temperature sensitive tape (170 degrees F) should be attached to a clean dry plate and the maximum registering thermometer can be attached with rubber bands to the outside of an inverted glass. If the tape changes color from silver or white to black or the maximum registering thermometer registers 170 degrees F or above and the wash and power rinse temperatures are within the proper range, the correct final rinse temperature can be assumed;

(f) Check that all the spray nozzles are properly aligned and unobstructed by debris or lime deposits and that all the curtains are in place;

(g) Determine that the flow pressure of the final rinse is 20 (+5) pounds per square inch. This is accomplished by observing the pressure gauge on the final rinse line;

(h) Assure that the timing of the wash and rinse cycles or the speed of the conveyor is within the manufacturer's specifications which may be found on a permanent type data plate affixed to each machine in a conspicuous location. This information may also be found in Table 1-2;

(i) Dishwashing machines which use chemical agents to sanitize the utensils must be evaluated to determine if a sufficient concentration of disinfectant is being applied to the utensil surfaces. Facilities must have on hand test kits or other devices which accurately determine the concentration of the sanitizing solution being used. The concentration of the sanitizing solution must be tested at frequencies which ensure correct concentrations throughout each machine use period. In addition, determine if there is an adequate supply of the sanitizing chemical on hand. Also determine if conditions allow complete air drying

(j) Observe whether or not the dishwashing machine and equipment are thoroughly cleaned after each meal period;

(k) Determine if proper safety precautions are observed during dishwashing operations.

a. Disassemble as necessary to permit access to all parts;

b. Scrape or rough clean to remove gross food particle accumulation,

c. Clean the equipment using a high pressure detergent spray, a line pressure spray detergent foam or a swabbing/brushing procedure using a detergent solution;

d. Rinse the washed equipment with potable water or detergent-sanitizer solution;

e. Manually swab or pressure spray the equipment with the concentration of detergent-sanitizer or chemical sanitizer specified on the label.