Application of Immersion heaters in the Cheesemaking Industry

A centuries-old art, cheesemaking requires skill and precision. Cheesemaking is a complex process involving dehydrating the milk, eliminating lactose and other ingredients in milk. This results in a concentrate of proteins and fat. The complexity of the process is due to the necessity for precision and the delicate balance of temperature and ingredients required to produce good quality cheese. 

The prime elements of the cheese are:

  • Salt – added in the salting process
  • Milk – the base ingredient
  • Coagulant – Rennet is commonly used
  • Starter cultures. 

The conversion of milk to cheese is a long journey which has the following important steps:

Pasteurization

The first step in preserving the milk is pasteurization. This step is also critical in preserving the quality of the product. Pasteurization eliminates the pathogens present in the milk. 

There are two major protein groups in the milk; whey proteins (which are roughly 20% of the total protein content) and caseins (which are roughly 80% of the total protein content). The caseins form a major part of cheese. The whey protein is a by-product of the cheese-making process and can be used to make ricotta. 

Coagulation

Coagulation is the second process in cheesemaking. Casein protein coagulates forming a cheese as the result of a physical and chemical reaction initiated by the lactic acid. The chemical reaction forms a network of proteins that physically results in coagulation.

Drainage

After the casein proteins coagulate they are separated from the whey protein in the drainage process. Drainage also involves the process of cutting and pressing the cheese. 

Salting 

As the name indicates the salt is added to either the surface of the cheese or within the body of the cheese.

Ripening

This is the last process in cheesemaking. The prepared cheese is ripened in an environment with controlled moisture and temperature where it is aged over months. This process is essential in the texture, quality, and flavor of cheese, producing important compounds.

Type of Immersion heaters used in cheesemaking

Immersion heaters are primarily applied during the pasteurization process. In this process, the milk is heated to 72˚C (161.6℉) for 15-20s or 60˚C-65˚C (140℉-149℉) for 30 min. Thus, eliminating the milk-borne pathogenic microorganisms. 

Another application of immersion heaters in cheesemaking leverages its precise heat transfer. Precision heating prevents overheating while maintaining temperatures at 47˚C (116.6℉) for 10-15 min. It is critical that the immersion heater selected is the right wattage because any less will result in the survival of harmful bacteria. Rising above the target temperature affects the quality of the cheese. Usually, a thermograph or temperature gauge is installed on the pasteurization tank to record the temperature. 

Scale of Cheesemaking Setup

In a small-scale setup (home-based) a portable immersion heater is generally operated by 120V and between 5 KW- 45KW power output. However, medium to large-scale setups mostly includes 100L to 200L tanks with motorized stirrers rotating at 25 rpm. The common material used is a food-grade stainless steel AISI 304/316. The outflow is controlled by a butterfly valve and the power supply is 400V at 50 Hz.  The heaters power 2000W and can maintain a temperature of 100L of milk at 72 ˚C to 75 ˚C with an accuracy of +/-2˚C to +/-5˚C. 

The immersion heater can be inserted directly in the pasteurization tank however more advanced systems used double jacket tanks where water is used in the inner lining to heat up the milk. In a simple analogy, this is a heat exchanger where heat is transferred from heated water to milk. This is becoming more popular because of the ability to keep the milk and water separate, thus improving the overall hygiene of the systems and the ability to change the immersion heater without emptying the main pasteurization tank. 

For the more traditional milk pasteurization “over-the-side” type immersion heaters are quite common because of ease of installation and maintenance however flanged heaters and threaded types are used in big industrial settings. 

Immersion heaters for Making Ricotta

Another related application to cheese making is using the immersion heaters for making ricotta. Whereas the cheese is coagulated using acidic or rennet coagulation, ricotta is coagulated by adding heat through immersion heaters. 

Whey protein is a byproduct of making cheese where casein protein is primarily used. At room temperature, they are hydrophilic, which means they are dissolved in water. However, whey protein coagulates once the whey water is heated. Usually, the mixture is heated to 75 ˚C to 85 ˚C, after some time the strands form and once the temperature reaches 82 ˚C and above they become visible to the human eye. They are skimmed soon after that. 

Selection of the Sheath Material 

Selecting the right sheath material makes a lot of difference in the longevity and reliability of the system. Even for benign service like heating of milk, the sheath material should be carefully suggested so that it does not provide a surface for the growth of bacteria. The preferred sheath material in Incoloy, titanium but they can be expensive, with a trade-off in the longevity of the system. PTFE based sheath materials are commonly used in the food industry as well as pasteurization of the milk. 

Conclusion

Immersion heaters are a fast and efficient medium of heating the milk and coagulant during various stages of the cheesemaking process. They provide precise heat to the mixture ideal for making good quality cheese. Important considerations in selecting the right material for the cheesemaking process is paramount because of the emphasis on selecting the food-grade material. Proper temperature control and monitoring is also required coupled with the immersion heater because of the narrow temperature window that is needed to achieve quality and texture in the cheese. 

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