Where did 3600
HUE come from?
Early Days
• Ordinance and Code Regulating Eating and
Drinking Establishments – U.S. Public Health
Service, 1943
– … irrespective of whether by hand or machine
• Immersion at least 2 minutes at 170-180°F or ½ minute in
boiling water (41,616 HUE’s by today’s standard)
• Mallmann, DeKoning, April 19471
• A rinse period of 10 sec. at 170°F for a single tank machine.
• Test soil was designed so that it would not be removed
during the entire process.
• Mallmann, Kahler, NSF 1949
• Immersion at least 30 seconds at 170°F (10,404 HUE’s today)
1 – Original study unavailable. Notes are from subsequent research report.
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HUE is “invented” and milk
pasteurization levels established
• Bactericidal Value of Dishwashing Machine
Sprays, Fuchs, 1951
– Curve defined by:
• M. tuberculosis and milk pasteurization
– 143°F for 1800 seconds, 161°F for 15 seconds ≡ 1800 HUE
– At an arbitrary temperature:
» HUE/sec = H = 3.03438E-17 X e 0.265972 X T
– No extra credit for temperatures above 165°F
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Pasteurization Defined
• High temperature/short time (HTST) Pasteurization
• The HTST pasteurization standard was designed to
achieve a 5-log reduction (0.00001 times the original)
in the number of viable microorganisms in milk. This is
considered adequate for destroying almost all yeasts,
mold, and common spoilage bacteria and also to
ensure adequate destruction of common pathogenic
heat-resistant organisms (including particularly
Mycobacterium tuberculosis, which causes tuberculosis
and Coxiella burnetii).
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FDA Food Code “Definition” of
Sanitization
• FDA Food Code in Chapter 1 Purpose and
Definitions under the section on sanitization.
– "Sanitization" means the application of
cumulative heat or chemicals on cleaned FOODCONTACT SURFACES that, when evaluated for
efficacy, is sufficient to yield a reduction of 5 logs,
which is equal to a 99.999% reduction, of
representative disease microorganisms of public
health importance.
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NSF
• NSF Summary Report: Study of Commercial
Multiple-tank Spray-type Dishwashing Machines,
March 1964
– M. phlei (more heat resistant than M. tuberculosis)
– Lower heat factors were required to destroy
microorganisms in water than in milk
– Organisms were suspended in capillary tubes at the
dish surface (thus preventing dilution or wash off)
– 1900 HUE required for “kill”
– “Kill” not yet defined as 5-log
– Concluded that the HUE method can be related to
micro-biological results
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NSF 1964
• For Mulitple Tank Conveyor Units
– Wash water 150°F
– Pumped rinse 160°F
– Final rinse 180°F
– Without reference to time exposures - However
typical timing would yield 9900 HUE!
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NSF 1977
• NSF Standard No.3, amended November, 1977
– 3600 HUE recommended
• Twice the recommended HUE for milk pasteurization
• More than sufficient to kill M. phlei
• Literature research suggests that 3600 was
established as an “arbitrary” safety factor of
2 times the value established for milk
pasteurization
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Evaluation of Household Dishwashing Machines for Use
in Small Institutions – Bryan, DeHart - 1975
• Regard 3600 HUE as providing considerable
margin
– It is twice the heat exposure required for pasteurizing
milk
– Bacteria in water are killed by a lower cumulative heat
factor than is required to kill bacteria in milk because
water is less viscous than milk
– The standard for pasteurizing milk, provides a
considerable margin of safety
– Pasteurization standards are based on the destruction
of large numbers of M. tuberculosis.
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The Sanitizing Efficiency Of Dishwashing
Machines – Vaughan 1979
• …effective soil removal should be the primary
feature of any dishwasher.
• 99.9% of the bacteria can be removed
simultaneously with the removal of soil
– Suggesting, mathematically, that only 2 log
reduction would be needed by sanitization
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Conclusions
• There is significant data and discussion
indicating that 1800 heat equivalent units is a
conservative requirement for the
pasteurization of milk
• Doubling the HUE requirement for a
warewashing machine adds an arbitrary
additional factor of 2
• Dishes are an indirect food borne illness path
to the human body, thus further reducing the
risk factor
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