end of the nozzle was 15 cm from the
stainless steel plate. The nozzle rotated to
one side to allow preclearing by directing
the vapor jet into a vacuum-driven funnel
to clear the steamer hose of cool water or
rotated to align with the center of the test
After exposure, the plate was
transferred to sterile tinfoil stored in
the pass-through chamber and then
transferred to a class II biosafety cabinet.
A sterile swab was immersed in sterile
phosphate-buffered saline (PBS) and
used to remove surface microbes by
swabbing. The swab was then immersed
in 500 µL PBS and vigorously shaken.
A 10-fold serial dilution series was
performed. The plate was labeled, placed
in an incubator and monitored for colony
Preliminary studies were conducted
to optimize various parameters as well
as test the exposure chamber and testing
procedures. CFU for mock exposures
(“control”) were variable. However
after an 8-second cleaning, in all food
substances tested, levels were reduced to
less than 1 percent or not detectable.
S. aureus subsp. aureus was added
to five common foods and either mock-cleaned or cleaned for 8 seconds using
the Optima Steamer.
For each bacterium, a specific
relevant food matrix was studied. S.
aureus and C. coli were reduced below
the limits of detection. L. monocytogenes
was reduced to an average of less than 1
CFU. There was no clear explanation for
the poor recovery of L. monocytogenes in
this test system. S. enterica was reduced
to less than 1 percent.
Recovery of four common food
pathogens was performed after addition
to the appropriate food matrix, application to a stainless steel plate and cleaning
for 8 seconds. Values were collected
for serial dilution as appropriate and
expressed as corrected for dilution CFU.
The results of the study demonstrate
that the dry steam cleaner studied, under
the optimized laboratory conditions
employed here, significantly reduced
food particles such that they could no
longer be seen, and significantly reduced
the pathogens studied here from stainless
steel after an 8-second cleaning. These
studies suggest that controlled use of a
dry steam cleaner is an effective method
to significantly decrease food pathogens
from stainless steel.
For complete studies, please visit
Food Processing Surface
Chemical-Free Dry Steam
Cross-contamination of food substances with pathogenic microbes during processing poses a significant health risk for the U.S. population as well as a
liability for food industries. Various bacteria can survive on hands, clothes and utensils
for hours or days after initial contact with the microorganisms.
Cross-contamination is best controlled with regular sanitation. One approach
is to sanitize surfaces and equipment at the end or beginning of each day or even
throughout the day, thereby limiting potential cross-contamination to a single date or
lot number. However, it may not be as simple as it sounds to disinfect surfaces using
traditional cleaning methods, including heat or chemicals. The chemical methods
typically employ strong oxidizers, which are most effective if allowed to react for
extended periods with use of adequate concentration and appropriate temperature
but are toxic for humans if ingested. Microorganisms have also developed survival
mechanisms to tolerate various stresses during food processing, including formation of
Current trends in the food industry are toward chemical-free cleaning. One
approach is “dry” steam cleaning. Dry steam is produced by a jet of superheated,
vaporized water that immediately evaporates, leaving behind little to no wastewater
production. This process dates back to the 1920s, when dry steam was used to remove
grease from heavy machinery. The jet of steam is highly effective at cleaning animal
fat and dried, otherwise difficult-to-remove substances from surfaces and equipment.
In the last two decades, smaller and drier units have been made available by suppliers.
Portable dry steam units can rapidly eliminate difficult-to-remove animal and plant
materials from surfaces and equipment. These units leave behind no residue and
are nontoxic, fitting well into green cleaning programs. In this study, one of the
higher powered and notably portable dry steam cleaners (the Optima Steamer TM,
manufactured by Steamericas Inc., Inglewood, CA) was evaluated for the efficacy of
removal of food substances and elimination of food pathogens in food substances from
Four microbes were selected: Staphylococcus aureus subsp. aureus, Listeria
monocytogenes, Campylobacter coli and Salmonella enterica subsp. enterica (ex
Kauffman and Edwards) Le Minor and Popoff serovar Choleraesuis.
Five food-like substances were selected: pasteurized whole vitamin D milk, sterile
organic beef broth, sterile organic chicken broth, sterile drinking water and sheep
blood. The selected test surface was a 4” × 4” custom stainless steel plate with holes
drilled at each corner for mounting.
The exposure chamber consisted of a modified glove box with a pass-through
chamber. The dry steam generator was in an adjacent room with a hose that entered
through the wall and then into the sealed exposure chamber. Deionized water was
used in the steamer, eliminating the need for an antiscaling agent that could potentially
contaminate food or introduce additional variables to the study. For all conditions, the
Excerpt from an FSM Signature Series article
By Lebrun Labs LLC / Dr. Stewart Lebrun