An alternative process for cleaning knives used on meat slaughter floors.
ABSTRACT Traditionally on slaughter floors operator knives are cleaned by rinsing in hand wash water at 20-40 degrees C followed by brief immersion in baths termed "sterilisers" which contain water no cooler than 82 degrees C. Under Australian legislation, both domestic and export, it is possible for a meat processing establishment to apply to the Controlling Authority for permission to implement an alternative procedure providing that it is at least the equivalent of that legislated. No firm evidence appears to exist for the 82 degrees C requirement and the possibility of replacing this element of the knife cleaning procedure with an alternative procedure using 60 degrees C water and a longer immersion time was investigated at an abattoir slaughtering cattle and sheep. Knives were tested at a range of work stations located along beef and mutton slaughter floors for Aerobic Plate Counts (APCs) and E. coli. For knives used on the beef chain the mean log APC/cm(2) was 2.18 by the current knife cleaning process and 1.78 by the alternate procedure (P<0.001). Using the current system E. coli was isolated from cleaned knives on 20/230 (8.7%) occasions compared with 21/230 (9.1%) occasions using the alternative system. The mean log E. coli of positive knives was 0.43/cm(2) and 0.61/cm(2) from the current and alternative systems, respectively. On the mutton chain the mean log APC/cm(2) was 1.95 using the current knife cleaning process and 1.69 by the alternative procedure (P=0.014). Using the current system E. coli was isolated from cleaned knives on 24/130 (18.5%) occasions compared with 29/130 (22.3%) occasions using the alternative system. The mean log E. coli of positive knives was 0.90/cm(2) and 0.76/cm(2) from the current and alternative systems, respectively. It is concluded that using two knives alternatively, rinsing them in hand wash water, then immersing them between uses in 60 degrees C water provides a microbiological outcome equivalent to rinsing them and momentary dipping in 82 degrees C water.
An alternative process for cleaning knives used on meat slaughter
Ian Eustacea, Jocelyn Midgleya, Charles Giarrussob, Chris Laurentb, Ian Jensonc and John Sumnerc
a Food Science Australia, PO Box 3312, Tingalpa DC, QLD 4170
b M. C. Herd Pty Ltd, 245 Bacchus Marsh Road, Corio, VIC 3214, Australia
c Meat & Livestock Australia, Locked Bag 991, North Sydney, NSW 2059, Australia
* Corresponding Author: Tel 61 7 3214 2117; Fax: +61 7 3214 2126
Traditionally on slaughter floors operator knives are cleaned by rinsing in hand wash water at 20-40°C
followed by brief immersion in baths termed “sterilisers” which contain water no cooler than 82°C. Under
Australian legislation, both domestic and export, it is possible for a meat processing establishment to apply
to the Controlling Authority for permission to implement an alternative procedure providing that it is at least
the equivalent of the legislated one. No scientific reasoning exists for the 82°C requirement and the
possibility of replacing this element of the knife cleaning procedure with an alternative procedure using 60°C
water and a longer immersion time was investigated at an abattoir slaughtering cattle and sheep. Knives were
tested at a range of work stations located along the beef and mutton slaughter floors for Total Viable Counts
(TVCs) and E. coli. For knives used on the beef chain the mean log TVC/cm2 was 2.18 by the current knife
cleaning process and 1.78 by the alternate procedure (p<0.001). Using the current system E. coli was isolated
from cleaned knives on 20/230 (8.7%) occasions compared with 21/230 (9.1%) occasions using the
alternative system. The mean log E. coli of positive knives was 0.43/cm2 and 0.61/cm2 from the current and
alternative systems, respectively. On the mutton chain the mean log TVC/cm2 was 1.95 using the current
knife cleaning process and 1.69 by the alternative procedure (p=0.014). Using the current system E. coli was
isolated from cleaned knives on 24/130 (18.5%) occasions compared with 29/130 (22.3%) occasions using
the alternative system. The mean log E. coli of positive knives was 0.90/cm2 and 0.76/cm2 from the current
and alternative systems, respectively.
Keywords: Meat industry; knife cleaning; alternative procedure; Australian Standard; equivalence; operator
It is a traditional part of the slaughter and dressing process for operators and inspectors to clean their knives
by first rinsing in tepid (20-40°C) water to remove soil and particles then to dip them in water maintained no
cooler than 82°C. This procedure is done between carcases with the aim of preventing cross contamination
between bodies. Baths termed “sterilisers” are supplied for knife cleaning at each work station. Prior to
metrication in Australia, water in sterilisers was required to be no cooler than 180°F – this temperature was
subsequently converted to 82°C; however, the scientific underpinning for this requirement is unclear.
A number of opinions may be found in the literature for suitable conditions for knife and equipment
sanitation. Some authors suggested that water for equipment cleaning should be heated to 140°F for one
minute or to 130°F for 5 minutes (Collins, 1954; Empey and Scott, 1939). Collins (1954) further stated that
knives and saws should be replaced and subjected to immersion in alkali at 160-180°F after twelve carcases
have been processed. Another statement is that the circular saw used for carcase splitting must be
periodically wiped clean of all visible blood and sawdust.
In the 1950s Dr Sloan, working for the USDA Agricultural Research Service (ARS) in Beltsville, Maryland,
is believed to have investigated methods of sterilising carcass-splitting saws. Sloan found that dipping
carcase-splitting saws in 180°F water killed sufficient numbers of organisms to satisfy regulatory
requirements. An alternative is that water at 82°C may have been chosen as the knife sterilisation procedure
that would kill the tubercule micro-organism Mycobacterium tuberculosis, the primary target organism in
milk and other foods at that time (Brewer, R., USDA, personal communication March 2002). Eventually
180°F water became the global standard for knife cleaning in all slaughter floor operations.
Recently, it has become possible under the Australian Standard for the Hygienic Production and
Transportation of Meat and Meat Products for Human Consumption (AS 4696: 2002) and the Export Control
(Meat and Meat Products) Orders for a meat processing establishment to apply to the Controlling Authority
for permission to implement an alternative procedure. Such an application must provide scientific data to
indicate the alternative procedure is at least equivalent to the one regulated.
As a precursor to the present study, Midgley and Eustace (2003) monitored the effect of cleaning knives in
lukewarm hand wash water then in sterilisers containing water cooler than 82°C. Inactivation was of the
same order as that obtained by momentary dipping in 82°C water and the researchers recommended that in-
plant trials be conducted using steriliser temperatures cooler than 82°C.
It was against this background that rinsing in hand wash water coupled with a two-knife system and 60°C
water was evaluated as an alternative procedure to the current system which involves rinsing then
momentary dipping of the knife in 82°C water. Under the alternative system each operator was provided
with two knives with, at any one time, one knife in use on the carcase and the other immersed in water at
60°C. The temperature of immersion water (60°C) was selected arbitrarily by abattoir management as one
which, if it could provide an equivalent outcome to 82°C water, would be advantageous for economic and
operator safety reasons. The evaluation was carried out according to a design in which, when the alternative
system was being trialled, knives always received a final treatment with 82°C water before being used on
2. Materials and Methods
2.1 Knife cleaning methods
The present study was carried out in an establishment with separate slaughter and dressing floors for cattle
and sheep, typical daily volumes for which were 500 and 3,000 head, respectively. Two regimes were
investigated for cleaning of knives. Under the current system the knife was cleaned by rinsing in hand wash
water at 20-40°C followed by momentary dipping in a “steriliser” maintained no cooler than 82°C. Under the
alternative cleaning regime a two-knife system of knife cleaning was used with rinsing as before, followed
by immersion in water at 60°C for the period while the other knife was used on the carcase, the operator
exchanging knives between carcases. A portable steriliser containing a thermostatically controlled heating
element (Ratek TH1 thermoregulator) was used to maintain a temperature at 60°C. A data logger was placed
in the steriliser to record water temperature during use.
2.2 Sponge sampling of knives
Knife blades were sampled immediately after the operator had cleaned the knife by one of the methods above
using a sterile polyurethane sponge (Nasco Whirlpak) hydrated in 25mL of 2 % (w/v) buffered peptone
water. The sponge was doubled over the back of the knife and the blade wiped from handle to tip. A
protective glove was worn by the operator beneath the rubber glove to protect against knife-cut wounds. Ten
knives at each station were tested, five knives in each of two trials.
2.3 Transportation of samples to the laboratory
After sampling, sponges in sterile bags were taken to the onsite laboratory for testing. In the laboratory,
samples were held in a refrigerator until analysed.
2.4 Determination of Total Viable Count (TVC) and E. coli
The sponge was squeezed firmly through the plastic bag and, from the liquid expressed, serial dilutions were
prepared in 0.1% buffered peptone water blanks (9 mL). Aliquots (1 mL) from each dilution were spread on
either Aerobic Plate Count Petrifilm (3M) and incubated at 20-25°C/3 days or on E. coli/Coliform Petrifilm
(3M) and incubated at 37oC for 2 days. Colonies were identified and counted as per the manufacturers
2.5 Statistical analysis
When E. coli was absent from Petrifilms the result was entered as “not detected”. TVCs were converted to
log10 cfu/cm2 and the mean of the log10 cfu/cm2 was calculated. The effects of the current and alternative
methods were compared using an Analysis of Variance. All calculations were performed with the statistical
software R (R Development Core Team 2005). The limit of detection for both TVC and E. coli was 0.36
Knives were tested at a range of stations located along the beef and mutton slaughter floors and E. coli and
Total Viable Counts (TVCs) obtained. In Table 1 are presented TVCs and E. coli prevalence on knives used
at stations along the beef chain. The overall mean log TVC/cm2 was 2.18 by the current knife cleaning
process and 1.78 by the alternative procedure. This constituted a significant overall difference in average
log TVC/cm2 (P-value < 0.001). However, this reduction was not consistent for each work station and
significantly larger falls were observed at tongue drop, head inspection and head boning stations, but no
significantly higher average log TVC/cm2 were observed with the alternate procedure at any of the 23 work
stations. In general, higher TVCs occurred earlier in the process, when cuts were made through the hide
particularly when air knives were used, or when knives were used at the head stations. Using the current
system E. coli was isolated from cleaned knives on 20/230 (8.7%) occasions compared with 21/230 (9.1%)
occasions using the alternative system. The mean log E. coli of positive knives was 0.43/cm2 and 0.61/cm2
from the current and alternative systems, respectively.
In Table 2 are presented TVCs and E. coli prevalence on knives used at stations along the mutton chain. The
mean log TVC/cm2 was 1.95 by the current knife cleaning process and 1.69 by the alternate procedure. This
constituted a significant overall difference in average log TVC/cm2 (P-value = 0.014). However, this
reduction was not consistent for each work station and significantly larger falls were observed at the
forequarter, pluck removal and pluck table stations, but no significantly higher average log TVC/cm2 were
observed with the alternative procedure at any of the 13 work stations. Higher TVCs were associated with
knives used to incise the brisket, trim exposed neck tissue, ring the bung (incise the anus) and remove the
viscera. Using the current system E. coli was isolated from cleaned knives on 24/130 (18.5%) occasions
compared with 29/130 (22.3%) occasions using the alternative system. The mean log E. coli of positive
knives was 0.90/cm2 and 0.76/cm2 from the current and alternative systems, respectively.
Midgley and Eustace (2003) demonstrated the effectiveness of an alternative procedure involving the
combined effects of rinsing the knife in hand-wash water prior to immersing it for 15 s at 72°C. These
researchers showed that, before they were washed, knives from the first leg and head stations were more
highly contaminated than were those from other stations (Table 3). The highest E. coli contamination was at
the first leg station, where the knife is often in contact with the hide during hide removal. When knives were
washed in hand-wash water (20-40°C) only, there were reductions in TVCs of around 0.7 log10 cfu/cm2 and
the prevalence of E. coli fell from 50% to 24%. After pre-washing, immersion of the knives in water at
72°C/15s or 82°C/1s effected further reductions of 0.5 log10 in TVC and to 8.3% in the prevalence of E. coli.
The present study extends the work of Midgley and Eustace (2003) and has, for the first time to our
knowledge, established a microbiological baseline for knives used along the entire beef and mutton chains
after the process termed “sterilising” (momentary dipping the knife in 82°C water). It is generally accepted
by microbiologists that this term is a misnomer with “cleaning” or “sanitising” more appropriate descriptors.
The present study indicates that faecal organisms are not always removed during knife cleaning and that
persistence of such organisms is related to the microbial load on the knife prior to cleaning. Thus knives used
for “dirty” operations such as incising areas of the hide/pelt which have faecal contamination, or freeing the
anus, are more likely to bear E. coli and to have TVCs >100/cm2 after the brief immersion at 82°C.
Contemporaneously with the present study a separate investigation of knife cleaning was undertaken at an
Australian pig slaughter and dressing facility. In Table 4 are presented TVCs and E. coli prevalence on
knives cleaned by momentary immersion in 82°C water at some stations along a pig slaughter chain
(provided by Reyes-Veliz, personal communication). The mean log TVC/cm2 was 1.98 with higher TVCs on
knives used to remove singed hairs (polishing) and at the backing off (incising to the backbone) stage. E. coli
was isolated from cleaned knives on 7/30 (23%) occasions and the mean log E. coli of positive knives was
Similar loadings on cleaned knives were found by Bell and Hathaway (1996) and Bell (1997) during sheep
and beef processing, respectively, in New Zealand abattoirs (Tables 5 and 6). Bell and Hathaway (1996)
measured the effect of knife cleaning at the work station where opening cuts on the hind leg of lamb carcases
are made. Before cleaning knives had a mean log TVC/cm2 of 5.04, reflecting the heavy soiling which can
occur at this site on the fleece. Rinsing the knife in hand wash water at 44°C removed 98.2% of
contamination (1.8 log reduction) from the blade and, after subsequent dipping in 82°C water, 99.8% of
contamination was removed to effect a 2.6 log reduction (Table 5). On the beef floor Bell (1997) found
contamination on knife blades approximated that of the hide on the hind legs (mean log TVC/cm2 of 3.61).
Cleaning the knife by rinsing in hand wash water then dipping in 82°C water reduced the loading on the
blade to mean log 2.64/cm2 – a 1 log reduction. The studies of Bell and Hathaway (1996) and Bell (1997) are
also of interest because they indicate that the knife hand was generally one log scale more contaminated than
the knife blade, both before and after cleaning.
The results of Bell and Hathaway (1996) indicate that most of the reduction in bacteria is attributable to the
spray rinse. Similarly, Midgley and Eustace (2003) found that rinsing the knives under streams of wash-
water before immersing in a steriliser removed at least 70% of bacteria. Importantly, thermal inertia of the
equipment prevents surfaces attaining the water temperature until several seconds have elapsed (Lowry,
1991) and Peel and Simmons (1978) showed that momentary immersion of knives at 82°C, on its own, was
ineffective in decontaminating knives of Salmonella. When fats or proteins are present on them, immersion
of knives at 82ºC for as long as 10 s will not give satisfactory reduction in bacterial contamination (Snidjers
et al., 1985). Also, hot water at 82°C was found to fix proteins onto the surface of the equipment (Weise and
Levetzow, 1976; Schütt-Abraham et al., 1988) leading to possible entrapment of bacteria. Midgley and
Eustace (2003) recommended a lower temperature and longer immersion time – a treatment that is possible
where a 2-knife rotation system is practised.
In an alternative system used in the present project, rinsing knives in hand wash water was followed by a 2-
knife system with 60°C water so that knives had a longer residence time. Residence time varied according to
work station from more than 30 seconds at legging on the beef floor to 1-2 seconds at the heads off and wax
eyes (teats removal) station on the mutton floor (data not included). On the beef floor, prevalence of E. coli
was similar for both cleaning systems (8.7% for the current versus 9.5% for the alternative system) and the
mean log TVC was lower (p <0.001) using the alternative system (1.78 versus 2.18/cm2). On the mutton
floor mean log TVCs were 1.95 for the current and 1.69 alternative knife cleaning systems (p=0.014).
However, prevalence of E. coli was higher using the alternative system (22.3% versus 18.5%). This
difference may reflect differences in lots being processed (and therefore, the knife loadings pre-cleaning).
From the current study it can be concluded that, after rinsing the knife in hand wash water, using two knives
and cleaning them in 60°C water provides a process equivalent to momentary dipping in 82°C water.
Midgley and Eustace (2003) listed potential benefits from using temperatures cooler than 82°C for cleaning
• Reduced risk of operator injury through scalding
• Reduced hot water consumption during knife and equipment cleaning
• Reduce impact of hot water on effluent treatment
• Reduced fogging and condensation
• Potential reduction in maintenance requirements
A change to 60°C water and its impact on improved occupational health and safety should not be
underestimated. It is thought that burns from steriliser water may account for around 10% of all industrial
injuries in an abattoir and limiting the amount of 82°C water would improve safety of operators.
We are grateful to the staff and management of M. C. Herd Pty Ltd, Corio, Victoria, Australia 3214 for their
patience, cooperation and financial contribution to this project. Funding was also made available by Meat &
Livestock Australia and the Commonwealth Scientific and Industrial Research Organisation. Luisa Reyes-
Veliz provided data on knife cleaning at a pig slaughter facility and we extend our thanks to the management
of that company for allowing data to be included in the present study.
Australian Standard AS4696:2002. Australian standard for the hygienic production and transportation of
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