Use of pH Meters at Pork Processing Plants

Pork quality and production efficiency can be enhanced through better selection and process control by monitoring the muscle pH of pork carcasses. This fact sheet, No. 2 in the Target Pork Quality series from BPEX, provides information to assist the industry in making use of pH measurement as a monitoring tool for quality management.
calendar icon 1 May 2012
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Benefits of Using pH Meters as a Monitoring Tool

Three key processing areas can substantially benefit from pH monitoring:

  1. Production efficiency: Carcass pH is directly related to the amount of drip loss and thus, the final yield of meat sold. Pork shelf-life is also greatly influenced by postmortem pH.
  2. Meat quality: pH is a good detector of poor meat quality. pH information could be used to segregate carcasses for more efficient use and to monitor process performance.
  3. Pig welfare: Poor pH carcasses may indicate a potential stress–related problem. These problems can be properly addressed only if identified.

Monitoring of carcass pH will help to identify production efficiency, meat quality and welfare problems. Corrective actions addressing these areas can only be taken after analysis of current trend or identification of specific problems.

"To improve productivity, quality or welfare in your factory: measure and monitor them FIRST!"


The muscle pH of living pigs is around 7.0 to 7.2. After slaughter, the lack of oxygen and nutrients reaching muscles triggers an enzymatic process called glycolysis. Lactic acid is built up in the muscle as a consequence of glycolysis. This induces a pH drop to about 5.5. The rate of pH fall contributes to a range of meat quality characteristics including colour, exudate and shelf-life.

pH values are measured generally at two time points: 45 minutes and 24 hours post-mortem, referred to as pH45 and pH24, respectively. There are two muscle conditions associated with abnormal pH fall: PSE (pale, soft and exudative meat) and DFD (dark, firm, dry meat). Both PSE and DFD characteristics are associated with poor production efficiencies, poor eating quality and in most cases, with animal stress.


PSE meat can be identified by a rapid initial pH fall (lower pH45) and slightly lower pH24. Pork with a pH45 lower than 6.0 is very likely to present PSE characteristics. PSE pork is wet, pale, low yield and tough when cooked. In addition to a genetic predisposition, PSE is caused by severe acute stress lasting for seconds or minutes immediately before slaughtering. Coercion, movement through the race, restraining, heat stress or mixing are common causes of acute stress.


DFD meat is characterised by a reduced extent of acidification and thus, a high pH24. Pork with a pH24 above 6.0 is very likely to present DFD characteristics. DFD pork is dark, firm and dry meat which is prone to spoilage and with poor processing potential. The main reason for DFD development is chronic stress which lasts for tens of minutes or hours before slaughter. Prolonged food deprivation periods, transport fatigue and fighting between unfamiliar pigs are frequent causes of chronic stress.

"Measurement of carcass pH is a monitoring tool which may help you improve production efficiency, pork eating quality and even welfare standards."

Routine carcass pH monitoring will allow you to:

  1. Picture the trend in quality of pigs being processed.
  2. Identify poor quality carcasss, preventing them from entering premium range products.
  3. Take corrective action, i.e. identification of particular farm or hauliers showing high incidence of abnormal pH carcasses.

Recommendations for taking measurements:

  • Measure 10 per cent of kill across producers on a different day each week
  • Always measure at the same time points, aiming for 45 minutes and 24 hours
  • Measure in the longissimus dorsi at the head of the last rib
  • Use an average of triplicate measurements where possible
  • Check calibration before every set of measurements, following manufacturers’ guidance
  • Ensure proper maintenance and cleaning of probes
  • Ensure staff are trained in use of pH meters

Commercially Available pH Meters

The lack of suitable commercial pH meters is the main reason given for the lack of routine pH monitoring. It is generally perceived that there is no easy-to-use, fast, food-approved, resilient and reliable equipment available.

As result, a trial comparing the performance of some commercial portable pH meters suitable for the food industry has been conducted by BPEX in collaboration with the University of Bristol through the Pork Chain Unit.

The best performing equipment is presented in the table opposite. The devices tested were both traditional measuring systems using glass electrodes (the first four devices) and ISFET technology which utilises a non-glass element (the last device).

The table illustrates some of the key parameters to take into account when selecting equipment for pH monitoring. Individual processors should decide which may be the most suitable for their individual requirements.

Accuracy*: the average difference between probe and control:
“3a*” = Average difference between probe and control was 0.2 pH units or less
“3b*” = Average difference between probe and control was 0.1 pH units or less

Precision**: the lower and upper limits of agreement:
“3a**” = The majority of measurements were within ± 0.5pH units or better
“3b**” = The majority of measurements were within ± 0.2pH units or better

“3”or “X” as assessed by a well trained person who took all the measurements through the whole practical exercise.

It was not possible to assess the life-time performance of the equipment but an indication of the guarantee period is given. Durability is an important feature but it should be noted that it is determined by how regularly the equipment is used and how it is handled, i.e. correct use, proper maintenance. According to the manufacturers, all devices assessed were food-approved, and the probes containing any glass components were made of special material which is break-resistant. Nevertheless, care is needed when handling glass electrodes in any food environment.

The pH manufacturing companies have expressed interest in the feedback from our trial and it is worth discussing your specific requirements with them. If there is sufficient demand, development may yield devices better suited for pork processors.


  • Both PSE and DFD characteristics are associated with poor production efficiencies, poor eating quality and in most cases, with stress-associated problems.
  • Measuring pH is a monitoring tool which may help you improve these factors.
  • All you need is a suitable pH meter and properly trained staff.

pH manufacturers/ suppliers contact details

NORONIX PHT 1140 meter + 130/77 probe
Separate Temperature Probe
Supplied by Klipspringer Instrumentation
01473 741500
[email protected]
and Sentek Ltd 01376 340456
[email protected]
Hanna HI 99163/FC 23D
Integrated Temperature Probe
Supplied by HANNA Instruments Ltd
08707 260010
[email protected]
Testo 205
Integrated Temperature Probe
Supplied by TESTO Ltd
01420 544818
Q 150 pH 57-SS
Integrated Temperature Probe
Supplied by EDT Direct ION Ltd
01304 829960
[email protected]
Testo 230/03
Separate Temperature Probe
Supplied by TESTO Ltd
01420 544818

May 2012

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