It is important to choose the right heat exchanger for the right product and process, whatever industry you are working in. However, for manufacturers of fruit products and fruit-based drinks the wrong system can affect not only operational efficiency or cost, but also product quality and consistency.

Today, the combination of pasteurization and aseptic filling is widespread due to its ability to ensure microbial product safety, provide the required shelf life and preserve flavor, aroma and texture. Different processing regimes can inactivate key enzymes, as well as generate new flavor or odor compounds, resulting in a different sensory profile. This is why manufacturers have increasingly adopted new processing techniques that maintain product quality. While alternatives exist to traditional pasteurization, thermal processing remains the preferred option globally as it is relatively cheap, reliable and effective.

Defining Fruit Product Quality

The sensory profile of fruit products, juices and fruit-based drinks are not determined by a single compound or chemical but by a complex mix of compounds including carbohydrates, fatty acids and amino acids. These nutrients interact with enzymes, converting them into metabolites that determine the sensory profile of the fruit or product, such as fatty acids, amino acids, terpenoids and furanones, color pigments, pectin, sugars and organic acids.

Therefore, the pasteurization process needs to be designed to retain the necessary organoleptic, chemical and nutritional qualities, while also creating a product that is free from microorganisms.

Choosing the Right Heat Exchanger

The exact choice of heat exchanger for fruit-based products depends on the physical and chemical nature of the product. Tubular heat exchangers are the standard choice for processing fruit products, but not all tubular heat exchangers are equal. Corrugated tube designs provide numerous benefits over the smooth tubes in tubular heat exchangers. 

In particular, corrugations create turbulent flow in the product, preventing viscous or suspended materials (like fruit puree) sticking to the wall of the tube, where they can form a boundary layer and prevent efficient heat transfer. In turn, this improved efficiency means that corrugated tubes provide greater levels of heat transfer than smooth tubes of the same length. As a result, corrugated tube heat exchangers can be up to half the size of their smooth tube equivalents. The turbulence created in the tube also reduces cleaning frequency and simplifies maintenance compared to other heat exchanger designs.

In practice, thicker materials such as fruit purees will often use a corrugated triple-tube heat exchanger. In contrast, products that contain particles or pieces will frequently use a corrugated double-tube design. Thinner and less viscous materials will benefit from corrugated multi-tube heat exchanger technology.

Fruit Processing Case Study

HRS previously provided an upgraded combined line to sterilize, cool and aseptically fill fruit purees for a major fruit processor in England.

The line was required to process two tons of product per hour without any negative impacts on product quality or texture, as well as offering the ability to switch quickly and cleanly between different batches and products. Built-in cleaning in place (CIP) facilitated this, allowing the system to cope with seasonal changes in product and different orders in quick succession.

In this installation the fruit puree enters from the production lines via a balance tank before being pre-heated and de-aerated, then heated to 201°F using an HRS AS Series triple-tube heat exchanger. The product is held at this temperature to ensure full pasteurization or sterilization as required. Heat for this process comes from water, heated via an HRS K Series multi-tube heat exchanger, which is derived from steam used elsewhere in the factory.

The system constantly monitors the temperature of the product; any product which has not been fully pasteurized or sterilized is returned to the beginning of the process. Once fully heat-treated, the puree is cooled, first to around 86°F using ambient water and another HRS AS Series heat exchanger, then cooled further to between 40°F and 50°F using chilled water. At the same time, the equipment itself, including the aseptic filling heads, is sterilized with hot water at 250°F. Sterility throughout the process is maintained with steam, which is automatically temperature controlled.