UHT Systems : Direct vs Indirect

UHT systems are commonly used in the food and beverage processing industry for products such as dairy, fruit juice, nutritional drinks, etc. As there are many ways one can achieve the desired level of heat treatment, the UHT system also has two primary methods in general.

Types of UHT Process

There are two primary methods when it comes to UHT processing- namely direct and indirect processing. The methods in which the products come into contact with the heat are different for each method. For indirect UHT treatment, there is a barrier between the steam (heating media) and the product. There are also several types of indirect UHT processing. Some of the most used indirect UHT processing methods are- plate heat exchange, scrape surface heat exchange, and tubular heat exchange for thick products that are prone to spoiling. Diary products, Coffee Creamers, and Stabilized Desserts are examples of good applications for indirect processing.

Direct Heat Processing is a more recent innovation in thermal processing techniques. In this method, products are physically mixed with the heating media. There are two subcategories of direct UHT processing – injection method and infusion method.

When using Infusion UHT systems, products are required to be put physically into the steam. In a typical infusion UHT system, the process starts by preheating the milk (or product) with a traditional PHT. After that, the product would go into what is known as an ‘Infusion’ vessel, which would be rained down by the steam filling the vessel very rapidly. This process takes only fractions of a second and raises the temperature of the product to the levels between 275-320 F. After the infusion vessel, the product goes into a short tube, followed by the ‘flash’ vessel. This flash vessel is used for two purposes- 1. To cool off the product as rapidly as it was heated up and 2. to ‘flash off the steam picked up in the infusion vessel. As the product became a little watered down after passing through the infusion vessel, and processing under the vacuum through the flash vessel, the excess water was pulled off while the product was being cooled down. Products that are a good fit for the Infusion UHT method are premium dairy products, baby food, lower-quality raw milk, and nutritional beverages.

For the Injection method, steam is directly introduced to the product. However, unlike the infusion method where the product is passed through the steam, the injection method removes the need for an infusion vessel. Instead, this method uses a special steam nozzle to inject the heating media directly into the product. Injection UHT systems still need to utilize a flash vessel to get rid of the steam used to heat the product. One big advantage of Injection system UHT processes is that they are less expensive than infusion systems. The trade-off, however, is that this method provides a bit less temperature control. Injection UHT systems are suitable for nutritional drinks, baby food, and premium milk productions.

However, one thing to note is that the direct heating process requires a relatively higher consumption of energy compared to the indirect UHT treatment (1).

Comparing the two systems: Advantages and Disadvantages

Advantages of Direct UH Treatment: As mentioned above, the product become diluted as a result of steam condensation coming into contact with the product during the direct heating process. An expansion vessel is used to remove the water condensation, as well as the incondensable gases and undesirable flavor- making the products taste better. The heating rate is also very high and it takes less than a second to attain the temperature needed for sterilization. Residue formation is minimal when using this method, allowing the plant to operate for a longer time without the need to clean.

Disadvantage of Direct UHT Treatment: The disadvantage of direct UHT process systems is that the cost of processing per milk unit volume is high. Additional equipment such as an aseptic homogenizer, and a vacuum expansion chamber, are needed and this makes the cost twice as high as the indirect type plant. The required level of heat energy is also very high making the water and electricity (25 to 50% more than indirect UHT systems). Direct UHT treatment also requires steam and a special boiler to process. Direct UHT treatment systems generate louder noises during the operational process as well.

Advantages of Indirect UHT Treatment: Indirect UHT treatment systems are simple in design. Fewer pumps and controls are needed to operate them. An indirect UHT system can also regenerate 90% of the required thermal energy. Another cost advantage of an indirect UHT system is that there is no need for an aseptic homogenizer and a special boiler which can be very expensive. Unlike the direct UHT systems, indirect systems are less noisy. Indirect UHT treatment systems require relatively lower operational costs and initial capital- making them ideal for cost-effectiveness.

Disadvantages of Indirect UHT Treatment: The rate of heat transfer is low for indirect heat exchanger types. The plant also requires more frequent cleaning as the residue deposit formation is bigger. As indirect UHT systems require more heat load, it can lower the acceptable product quality level as well. In order to remove the dissolved oxygen from the milk (product), an additional equipment called a ‘deaerator’ is needed.

Which One Should You Choose: Direct or Indirect UHT Treatment??

As each method has its own advantages and disadvantages, it has always been a dilemma for business owners when choosing the method for their process lines. To make it simple, the most basic question one should ask themselves is what kind of product will be treated for the UHT process. Other factors such as the quantity of products to be processed, estimated cost of production, and the expected profit margin should also be considered to optimize the profits.

If you need further consultation to choose the perfect UHT method for your processing lines, do not hesitate to contact MUNINMAX’s sales engineers for consultation. Our team of experts has over 20 years of experience and can give you the best insights to choose the most beneficial UHT method for your business. Contact our sales engineers at [email protected] for more details or visit our website www.muninmax.co.th to find out more about our product line.