1 

THE FEASIBILITY OF USING HOUSEHOLD STEAM CLEANERS TO CONTROL 

MICROBIAL QUALITY OF ANIMAL CARCASSES IN SMALL AND VERY SMALL 

MEAT PROCESSING PLANTS 

A Final Progress Report to USDA FSIS 

Jinru Chen 

Department of Food Science and Technology 

The University of Georgia 

October 7, 2005 
2 

Phase I - Laboratory Studies 

Methodology 

Three different commercial household steam or steam/vacuum cleaning systems, S1, S2, and S3 

(Figure 1), were purchased from two different suppliers (Table 1). Each cleaning system 

differed from the others in their technical parameters (Table 1). System-1 (S1) was a household 

steam cleaner with a high steam capacity power of 1,500 W. System-2 (S2) used a combination 

of steam (1,000 W) and vacuum (800 W), producing a high temperature steam (248o

F) at 58 psi 

(4 bars), whereas, system-3 (S3) was a vapor cleaning system with the highest capacity of 1,600 

W, producing low moisture steam at high pressure (85-95 psi). 

A 

B

C 

FIGURE 1: Household steam cleaners used in the study. A). Cleaner S1- Steam Fast SF 275; B). 

Cleaner S2 œ Steam Fast SF850; and 3). Cleaner 3 œ Super Vapor 6. 

Table 1. Detailed information on the household steam cleaners used in the study. 

Steam Supplier System Specification Cost Meat Surface Meat Surface 

Cleaner Temperature Temperature 

after 30 sec after 180 sec 

S1 Top Innovations steam 1,500W $149.99 45oC 87oC 

SF 275 

S2 Top Innovations steam 1, 000W & 248o

C $899.99 33oC 71oC 

SF 850 vacuum 800 W & 58 psi 

S3 Vapor Systems vapor 1,600W &85-95 psi $1495.00 27o

C 66oC 

Super vapor 6 
3 

Blocks of pork skins (7 X 3.5 cm2), inoculated with a 5 strain-mixture of Escherichia coli 

O157:H7 or Listeria monocytogenes at 107 and 105 CFU/10 cm2

, respectively, were divided into 

three groups with 12 inoculated pork skin pieces in each group. Each group of the pork skin 

blocks was treated with S1, S2, or S3 for 30, 60, 90, 120, 150, and 180 sec, respectively, and the 

treatment was duplicated at each time interval. Each trial was conducted twice and during each 

trial, two inoculated pork skin pieces were run as positive controls which were not subjected to 

any steam or steam/vacuum treatment. Additionally, two skin pieces not inoculated with the 

pathogens were run as negative controls. All of the samples were transferred, following the 

steam treatment, to a bucket of ice for immediate chilling. 

The treated pork skins were sampled by aseptically excising the 5 X 2 cm2 inoculated area with a 

sterile pair of scissors. Each of the skin samples were aseptically transferred to a sterile 

sampling bag containing 10 ml of sterilized maximum recovery diluent (MRD). The contents of 

the bag were subjected to stomaching for 1 min at normal speed using a Stomacher 400 lab 

blender. Serial dilutions were prepared using sterilized MRD. A 50 μl of appropriate dilutions 

was plated in duplicate onto sorbitol MacConkey agar (SMAC) with Cefixime-Tellurite (CT) 

supplement (Dynal biotech, Oslo, Norway; CT-SMAC), Oxford medium base with modified 

Oxford antimicrobial supplements (MOX), tryptic soy agar (TSA), and MacConkey (MAC) agar 

plates, respectively for the enumeration of E. coli O157:H7, L. monocytogenes, total aerobes, and 

thermoduric bacteria, respectively, using the Autoplate® 4000 automated spiral platter. The 

inoculated plates were incubated under appropriate conditions before colonies were counted 

using the QCOUNTTM automatic colony counter (QCOUNTTM software, Spiral Biotech, Bethesda, 

MD, USA). All media used in the study were purchased from Difco Laboratory (Sparks, MD) 

unless otherwise specified. Data obtained was analyzed statistically based on a 95% confidence 

level. 

The surface temperatures of the pork skin pieces, while receiving the steam treatment from S1, 

S2, or S3, were recorded using a traceable dual channel thermometer with offsets (Fisher 

Scientific). Each channel was connected via K-type beaded probes which are designed to 

measure the surface temperature. Both probes were attached to the pork skin surfaces and 

temperature readings were recorded for each treatment time and for all three steam systems. The 

temperature readings were plotted as a function of steam time. 

Results 

The application of steam and steam/vacuum generated by S1, S2, and S3, respectively caused a 

reduction in the populations of E. coli O157:H7 up to 7.38, 4.85, and 5.79 Log10 CFU/cm2 

(P<0.05), respectively, with a treatment time of 60, 180, or 180 sec at the 107 CFU/10 cm2 

inoculation level (Figure 2A). Whereas, at the 105 CFU/10 cm2

 inoculation level, the reduction 

in E. coli O157:H7 populations caused by S1, S2, and S3, respectively, was 5.70, 5.70, and 5.45 

Log10CFU/cm2 (P<0.05), respectively, with a treatment time of 150, 150, or 180 sec (Figure 3A). 
4 

A 

8

7

6

5

4

3

Log10 CFU/cm2 

2

1

0

S3 

S2 

S1

0 30 60 90 120 150 180

Time (s) 

B 

0 

1 

2 

3 

4 

5 

6 

7 

8 

10

2 

S3 

S2 

S1

Log CFU/cm

0 30 60 90 120 150 180

Time (s) 

C 

0 

1 

2 

3 

4 

5 

6 

7 

8 

10

2 

S3 

S2 

S1

Log CFU/cm

0 30 60 90 120 150 180

Time (s) 

FIGURE 2. Survival of E. coli O157:H7 (A), total aerobes (B), and thermoduric bacteria (C) on 

pieces of pork skins (5 X 2 cm2

), inoculated with approximately 7 Log10 CFU/10 cm2 of E. coli 

O157:H7, as influenced by 30, 60, 90, 120, 150, or 180 sec of steam or steam/vacuum treatment 

with the household cleaning system S1 (▲), S2 (■), and S3 (♦). 
5 

A 

0 

1 

2 

3 

4 

5 

6 

10 / 2 

S3 

S2 

S1

Log CFU cm 

0 30 60 90 120 150 180

Time (s) 

B 

C 

0 

1 

2 

3 

4 

5 

6 

10 / 2 

S3 

S2 

S1

Log CFU cm 

0 30 60 90 120 150 180

Time (s) 

6

5

4

3

2

1

0

0 30 60 90 120 150 180 

10

2 

S3 

S2 

S1

Log CFU/cm

Time (s) 

FIGURE 3. Survival of E. coli O157:H7 (A), total aerobes (B), and thermoduric bacteria (C) on 

pieces of pork skins (5 X 2 cm2

), inoculated with approximately 5 Log10 CFU/10 cm2 of E. coli

O157:H7, as influenced by 30, 60, 90, 120, 150, or 180 sec of steam or steam/vacuum treatment 

with the household cleaning system S1 (▲), S2 (■), and S3 (♦). 
6 

The application of steam, generated by the three household cleaners, for 180 s caused a reduction 

in the populations of L. monocytogenes up to 7.61, 6.91, and 5.78 Log10CFU/cm2

, respectively, 

from the initial level of inoculation of 107 CFU/10 cm2

 (Figure 4A). The same treatment resulted 

in a reduction of 5.75, 4.04, and 3.23 Log10CFU/cm2, respectively, on the pork skin samples 

having an initial Listeria population of 105 CFU/10 cm2

 (Figure 5A). 

A similar reduction trend was observed with total aerobic and thermoduric bacteria counts on 

pork skin inoculated with E. coli O157:H7 (Figure 2B, 2C, 3B and 3C) and L. monocytogenes 

(4B, 4C, 5B and 5C) at both 107

 and 105 CFU/10 cm2 inoculation levels. Significant differences 

were observed between different inoculation levels (107

 and 105 CFU/10 cm2), treatment times 

(30, 60, 90, 120, 150, and 180 sec), and types of cleaning systems (S1, S2, and S3) used in the 

study (P<0.05). These results indicated that the evaluated household cleaning systems 

effectively reduced the levels of both pathogenic and spoilage microorganisms under the tested 

laboratory conditions. 
7 

A 

0

1

2

3

4

5

6

7

8 

10 

2 

S3 

S2 

S1

log CFU/cm 

0 30 60 90 120 150 180

Time (s) 

B 

0

1

2

3

4

5

6

7

8 

10

2 

S3 

S2 

S1

log CFU/cm 10 2 

S3 

S2 

S1

log CFU/cm 

0 

0 

7

6

5

4

3

2

1

0

C 

30 60 90 120 150 180

Time (s) 

30 60 90 120 150 180

Time (s) 

FIGURE 4. Mean populations of (A) L. monocytogenes, (B) total aerobes, and (C) 

thermoduric bacteria recovered from pork skin samples, inoculated with 7 Log10 CFU/10 cm2

of L. monocytogenes, after treatment with steam or steam/vacuum for 0, 30, 60, 90, 120, 150, 

or 180 sec using three household cleaning systems S1(▲), S2(■) or S3(♦). 
8 

A 

0

1

2

3

4

5

6

7 

10 

2 

S3 

S2 

S1

log CFU/cm 

0 30 60 90 120 150 180

Time (s) 

B 

0

1

2

3

4

5

6

7

8 

0 (s) 

log10 2 

S3 

S2 

S1 

C 

0

1

2

3

4

5 

0 

(s) 

log10 2 

S3 

S2 

S1 

30 60 90 120 150 180 Time

 CFU/cm

30 60 90 120 150 180 

Time

CFU/cm

FIGURE 5. Mean populations of (A) L. monocytogenes, (B) total aerobes, and (C) 

thermoduric bacteria recovered from pork skin samples, inoculated with 5 Log10 CFU/10 cm2

of L. monocytogenes, after treatment with steam or steam/vacuum for 0, 30, 60, 90, 120, 150, 

or 180 sec using three household cleaning systems S1(▲), S2(■) or S3(♦). 
9 

The surface temperatures of the pork skin while receiving treatment of steams generated by the 

three cleaning systems are summarized in Figure 6. The skin samples treated by S1 had 

relatively higher surface temperatures in comparison to the samples treated by S2 and S3, and the 

samples treated by S2 had relatively higher surface temperatures than the samples treated by S3. 

The surface temperatures of pork skin samples correlated with the results of microbial 

inactivation studies, in which S1 had superior performance to the other two cleaning systems. 

The increases in pork skin surface temperatures obtained by S1, S2, and S3 were in order of 45o

, 

33o

 and 27oC, respectively in the first 30 sec of steam treatment (Figure 6). At the end of the 180 

sec treatment, the surface temperatures of the pork skin samples treated by S1, S2, and S3 

elevated to 87o

, 71o, and 66oC, respectively. Because of its better ability in raising meat surface 

temperatures, S1 was selected for inactivation of pathogenic and spoilage microorganisms on 

animal carcasses in small and very small meat processing plants. Temperature ( oC) 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

S3 

S2 

S1 

0 50 100 150 200 

Time (s) 

FIGURE 6. Surface temperature of pork skin samples treated by household steam cleaner S1 

(▲), S2 (■), and S3 (♦) for 30, 60, 90, 120, or 180 sec. 
10 

Phase II - In Plant studies 

Methodology 

The effectiveness of the household steam cleaners in reducing the levels of total aerobes, 

coliforms, and enterobacteriaece was evaluated using a total of 70 beef, and 70 hog carcasses 

from 4 different small or very small meat processing plants in Georgia. The left side of a beef or 

hog carcass was used as controls whereas, the right side of the same carcass was treated for 180 

sec with the steam generated by cleaner S1, which has been proven to be the most effective 

cleaner in laboratory studies. The levels of total aerobes, coliforms, and enterobacteriaece on 

three different anatomical locations of the beef (neck, midline, and rump) and hog (ham, belly, 

and jawl) carcasses were determined before and immediately after the stream treatment. 

Results 

The overall statistical analysis of the results from the 420 samples of the 140 animal carcasses 

revealed that the 180 sec steam treatment by S1 significantly reduced the populations of total 

aerobes, coliforms, and enterobacteriaece (P<0.05) (Table 2). The results in Table 3 showed 

that, after the steam treatment, the populations of total aerobes, coliforms, and enterobacteriaece 

on the neck, midline and rump areas of the beef carcasses as well as on the jawl, belly and ham 

areas of the hog carcasses were significantly lower (P<0.05) than the populations of the same 

types of microorganisms on the respective anatomical areas of each type of animal carcass 

evaluated in the studies. 

Table 2. Overall mean populations (Log10 CFU/cm2

) of total aerobes, coliforms, and 

enterobacteriaece recovered from the three anatomical locations of beef and hog carcasses, 

before and immediately after the steam treatment using a commercial household cleaning system 

(n=420). 

Sampling time Total aerobes Coliforms Enterobacteriaece 

Before 2.19 a 2.15 a 1.62 a 

After 0.75 c 0.83 c 0.36 b 

* Means in the same column followed by the same letter are not significantly different.
11 

Table 3. Mean populations (Log10 CFU/cm2) of total aerobes, coliforms, and enterobacteriaece 

recovered from the three anatomical locations of beef and hog carcasses, before and immediately 

after steam treatment using a commercial household cleaning system. 

BEEF HOG 

(n=70) (n=70) 

Rump Midline Neck Ham Belly Jawl 

Total aerobes 

Before 1.83 a 1.94 a 1.87 a 2.06 a 2.91 a 2.52 a 

After 0.79 b 1.15 b 1.06 b 0.24 b 0.59 b 0.67 b 

Coliforms 

Before 1.53 d 2.02 d 2.11 d 1.95 d 2.94 d 2.34 d 

After 0.38 e 0.84 e 0.92 e 0.82 f 1.30 f 0.70 e 

Enterobacteriaece 

Before 1.27 g 1.47 g 1.35 g 1.34 g 2.19 g 2.12 g 

After 0.20 h 0.71 h 0.65 h 0.08 h 0.28 h 0.26 h 

* Means in the same column followed by the same letter are not significantly different.