Don’t let your tempering and defrosting solutions let you down

PHT has carved a niche in the local food hygiene arena with specific emphasis on workable solutions for the meat and poultry industry. Maryke Foulds attended its latest virtual session where the science behind freezing, tempering and thawing was under discussion.

Professor Elana Buys of the University of Pretoria explained that freezing is a key technology that causes minimal changes to the quality of food including parameters such as shape, weight and microbial load of the product.

Food is normally frozen to an internal temperature of -18°C and this temperature must be maintained during transport and storage which prevents microorganisms from multiplying. The freezing process doesn’t kill all types of bacteria and those that survive can multiply more rapidly than before freezing.

During freezing, liquid forms solids or small and large ice crystals but this process does not inactivate the enzymes found in the product. They remain active although in a reduced rate.

During quick freezing, ice crystals are smaller, resulting in less damage than a product frozen slowly. Freeze thaw stability is one of the important physical properties relating to the substance that allows it to be frozen and then thawed without damage to its structure or properties.

Freezing prolongs the shelf life of products by slowing microbial growth and enzyme activity. In general the lower the temperature within the frozen storage, the lower the rate of microbiological and biochemical changes. Relatively high storage temperature of between -4 to -10 C have a greater lethal effect on microorganisms than lower temperatures of -15 to -13.

Different kinds of microorganisms vary in their resistance to lower temperatures.

When frozen food is thawed using air or water, the surface ice melts to form a layer of water. Water has a low thermal conductivity and a lower thermal conductivity than ice. The surface layer of water therefore reduces the rate at which heat is conducted to the frozen interior. The insulating effect increases as the layer of thawed food grows thicker.

During thawing the main considerations are to avoid overheating and dehydration of food. As opposed to home thawing, commercial thawing is done in a vacuum chamber by condensing steam, by warm water or by moist air that is recirculated over the food.

The changes that occur when thawing food depend on the speed of the thawing. Along with the time the food is held close to its freezing point, the rate of freezing and the temperature abuse during storage. This in turn determines the damage caused to the cellular structure and hence the amount of drop loss on thawing. For these reasons, thawing is not simply the reverse of freezing.

Drip losses cause loss of water soluble nutrients – beef losses can be up to 12% thiamine, 10% riboflavin, 14% niacin, 32% pyridoxine and 8% folic acid. Drip losses also form substrates for enzyme activity and microbial growth. The lack of proper cleaning or blanching can result in pathogenic spoiling. It is critical that temperature abuse must not take place in the cold chain. If it does occur you must check quality paraments and microbiological activity.

Microbiological contamination of food before freezing is caused by inadequate cleaning of food. Inadequate blanching has a pronounced effect during this period and can permit growth of psychotropic spoilage and pathogenic microorganisms.

DEFROSTING SOLUTIONS FROM SCHRÖTER TECHNOLOGIE

Jens Wittig’s presentation on Climajet offered an insightful look at the defrosting of different food products. The technology offers individual air flow systems for processes throughout the entire production chain – from defrosting through to cold smoking, maturing, and post-maturing.

The innovative Climajet defrosts frozen foods very gently and without loss of quality. The air-conditioning process control system and horizontal air flow guarantee uniform defrosting results with a minimum weight loss and natural freshness – even for solid blocks of frozen meat.

Frozen meat must be defrosted from –24°C to about -1/0°C before it can be processed. Up to now, this has been done using a water bath. The disadvantage here is the high water consumption and compromised meat quality due to leaching.

Thanks to a new steam defrosting procedure, the plants from Schröter not only decrease losses from defrosting but also reduce power consumption to one tenth. The deep-frozen meat blocks are stored in mobile frames on several layers for this purpose. Steam is blown in and heats the defrosting room to the required set point, ensuring a uniform distribution of heat. Fans ensure that optimal heat distribution is guaranteed through horizontal air flow. Insertion sensors directly underneath the surface of the product and at the core of the product control the uniformity of the defrosting process. The system always operates within the optimum range so that excess temperatures and germ growth in the defrosting goods can be prevented.

BENEFITS OF USING THE CLIMAJET TECHNOLOGY

• Uses high quality brand products like Allen Bradley, Festo

• Less defrosting weight loss, compared to a water bath

• Good microbial status

• Energy savings

• Flexile use of defrosting room (defrosting, drying and cooling storage)

• 100% batch traceability by means of process visualisation

• Hygienic design

• CIP cleaning system is standard on every installation.

DEFROSTING AND TEMPERING SOLUTIONS

Sairem’s Mathieu Deschamps looked at how microwave and radio frequency energies can be used in the food processing industry for cooking or tempering deep frozen products. Recent advances have opened up new applications for pasteurising, desensitisation, drying and boost heating certain ingredients. Adapted solutions exist for dry goods, liquid and pastes, processed food or ready-to-eat meals.

New industrial applications, mainly in heating and drying processes have shown outstanding results in terms of speed, quality control, process repeatability and energy control. Sairem offers a full range of solutions to thaw foodstuffs quickly and efficiently, while still preserving the organoleptic properties. Unlike other manufacturers, Sairem’s offer includes both microwave and radio frequency machines, and depending on the process and the characteristics of the ingredients to temper, it will supply you with the highest performance machine with the right technology and frequency for your application.

The speed and uniformity brought by the microwave and radio frequency processes minimise the product drip losses and degradation. By completely eliminating the weight losses caused by conventional defrosting methods (which can represent up to 10% of the ingredients to be transformed) you immediately improve your raw material yield. The payback can be as short as 6 to 12 months. For example, if you defrost 20 tonnes of product per day, you could save close to R80 000 per day thanks to Sairem’s tempering solutions.

Defrosting by microwave takes from three to 10 minutes instead of hours or days with traditional methods, even for large food blocks. Ingredients don’t need to be unpacked and can be processed in the units inside the plastic film, the cardboard or plastic box saving on labour and processing time. The equipment features a small footprint, as it replaces large tempering or defrosting rooms. The buffer stock created by the traditional defrosting duration is eliminated. Equipment capacity is highly scalable thanks to its modularity and as processing needs grow industrial defrosting equipment can easily be upgraded.

Bacterial growth will be limited thanks to the rapidity of the process. In traditional processes, frozen ingredients take hours if not days to reach the right processing temperature, with a significant risk to food safety. The final temperature is not controlled accurately and may go above 0°C. Microwave and RF tempering is complete in a matter of minutes with perfect control of the final temperature. On demand, and for optimal food safety, tunnels allow you to separate the incoming and outgoing product flows to avoid cross-contamination. •