Measuring Temperature and Pressure in the Canning Industry

In 2009, nine people died when they consumed peanut butter contaminated with salmonella. This resulted in three Peanut Corporation of America executives receiving long sentences for their role in the outbreak. The lesson from this should be crystal clear: food manufacturers and processors must guarantee the safety of their products.

FDA regulations necessitate verification of processes meant to render food products safe for human consumption. In the case of canning (a preservation and packaging process using heat and pressure) it is crucial to validate process performance to guarantee suitable treatment is being carried out. Moreover, records of such verifications must be maintained as proof of so doing.

Much of what follows is relevant to other thermal sterilization procedures, such as those using autoclaves. However, this article is intended specifically for those involved in the food processing and packaging sectors.

Background to Food Canning

Besides fresh meat and produce, a lot of the food sold today is well-maintained by freezing. A newer process, High Pressure Processing (HPP) is finding increasing use as a substitute to freezing. It uses a combination of heat and pressure to kill microbial contamination and pathogens and in this regard is similar to the much older process of canning.

Canning as a technique for preserving food for storage and transportation was developed early in the nineteenth century (the can opener however was not invented for another four decades). In canning seafood, fresh meat, fruit or vegetables – it is cleaned, prepared, and packed into a metal canister (therefore the origin of the word) containing syrup or water. The can is sealed and passed into an oven for cooking. Liquid is vaporized by the heat, which increases the pressure within the can. Heat, united with pressure, kills or renders inactive pathogens and microbial contamination, preserving the food almost forever. A specific concern is to destroy spore forming bacteria such as Clostridium Botulinum, which is a lot lethal if consumed.

Canned foods are heated to 116 to 121 °C (240 to 250 °F) and maintained at this temperature for a time related to the food’s density, acidity, and heat transfer properties. Corn particularly requires a longer time to guarantee the elimination of any contamination.

Process Verification

Food processors have to conform to the requirements of 9 CFR 417.2 - Hazard Analysis and HACCP Plan (HACCP is short for Hazard Analysis and Critical Control Point). In summary, this requires that they:

• Document the steps in the processes used for each product
• Identify areas of potential contamination
• Develop and implement a plan to prevent or remove contamination
• Implement procedures to confirm the adequacy of the plan

Pocket infrared thermometer

For canners this means proving that their processes maintain conditions that will kill or render all pathogens inactive, including C. Botulinum. This sort of substantiation is best performed with instrumentation such as a temperature data logger for food.

Temperature Distribution

Devices are available to log both temperature and pressure on a time basis. Such data can then be downloaded into a PC for storage and analysis. However, recording a single set of data only reveals the conditions experienced at the location where the data logger was placed. As many ovens have an irregular temperature distribution, it is sensible to use multiple loggers distributed all over the chamber. For instance, it may be considered sensible to log conditions in the eight corners as well as the midpoint. Alternatively and especially if a specific distribution is anticipated, a range of loggers might be positioned to enable thermal mapping of the chamber.

Pressure Data

Capturing useful pressure information is significantly more complex than recording temperature. First, a submersible data logger is required. Second, the pressure within a can relies on the quantity of liquid included, as well as the volume available for expansion. Thus, while a logger can be kept inside a can, the contents must be tweaked to reflect the difference between the logger and the typical contents. Also, do not overlook the significance of plainly distinguishing the can from the rest of the oven contents so it may be retrieved prior to shipment.

Calibration and Traceability

As with any instrumentation, calibration and traceability based on National Standards are advised to guarantee the validity of the data. Organizations having in-house laboratory facilities may carry out this themselves. Alternatively, temperature and pressure loggers can be bought with certificates of NIST traceability.

USB output sanitary fitting pressure transducer

Temperature and Pressure Data Loggers

OMEGA Engineering’s OM-CP-PRTEMP140 Series of high temperature and pressure data logger overcomes the need for a submersible thermocouple and is meant for applications such as verification of thermal sterilization procedures in the canning sector. This compact IP68-rated package made from 316-grade stainless steel records both temperature and pressure, and comes with a NIST calibration certificate.

In contrast to devices using a submersible thermocouple, this logger adds an RTD spanning a range of -20 to 140 °C (-4 to 284 °F) with a resolution of 0.01 °C (as peak temperatures are below 200 °C, a very high temperature data logger is not needed). Pressure is measured by strain gauge with a range of 0 to 5 bar and 0.0001 bar resolution. More than 32,000 data points may be recorded, at a rate of one per second to once every 24 hours. The start of recording is programmable or can be started manually. On recovery from the oven, data can be downloaded by connecting the logger to a PC. Alternatively, the logger may be linked to a PC while in use for real time data capture.

Autoclave temperature data logger

Summary

Consumer protection is of the greatest concern across the food sector. FDA procedures mandate a HACCP approach which stipulates that companies identify risk points, implement control measures, and verify that those measures are effective.

Canning is a food preservation and packaging procedure that depends on heat and pressure to destroy pathogens and microbial contamination. However, these will be useless if minimum temperatures and times are not realized. A combined temperature and pressure data logger such as the OMEGA^® OM-CP-PRTEMP140 Series, captures this process data at a frequency stated by the user and allows it to be downloaded onto a PC for further reference. Such data loggers are thus a vital component in guaranteeing safety all the way through the food chain.

This information has been sourced, reviewed and adapted from materials provided by OMEGA Engineering Ltd.

For more information on this source, please visit OMEGA Engineering Ltd.