Develop recipes for success

For food quality like homemade, what’s the right kind of heat?

Choosing the right method of heating for prepared food applications is a delicate task. This is mainly because the heating process not only ensures that the product is safe from a microbiological perspective, it also actually cooks the ingredients. Much like what happens in kitchens all over the world, we use heat to achieve a desired taste and texture.

Heating can produce desired qualities, including:

  • Thickness in a swelling starch product, e.g. soups and sauces.
  • Particle softness and taste, e.g. vegetable stews and rice desserts. 
  • Taste, when long-term heating brings out flavour, e.g. bean pastes and hummus.

Tetra Pak’s portfolio boasts a large selection of heating equipment, enabling us to provide you with the optimum heating solution for your needs. We have the ideal solution for you, but to get there let’s first think about what heating prepared foods involves.

Applications within the prepared food category include soups and sauces, desserts and fruit preparations, tomato applications, liquid nutritional products and cream cheese. Within all subcategories there are product varieties, some containing particles and others with a smooth appearance and texture. In addition, desired product viscosities can range from very thin and free-flowing liquids to almost sliceable processed cheeses. Product textures can be achieved via natural starches or gums, which react differently to heating, but can also come from fermentation or enzymatic reactions. Different product characteristics will result in different demands on the heating process.

Now we know what we’re talking about, let’s look in more detail at some of the challenges of heating prepared food

Particle content – heat to the core

Particulate products make up a growing segment of the market, not only as prepared foods with applications like fruit preparations and soups, but also beverages, such as nata de coco (jellied coconut juice) or tea containing aloe vera pieces.

Particulate solutions require special consideration for heat treatment. First and foremost, the nature of particles means the calculation of the right heat treatment must consider the time it takes the desired temperature to reach the centre of the particles, while also maintaining their integrity. This varies depending on particle size, shape and composition, as well as density, thermal conductivity and heat capacity. Naturally, when it is necessary to cook the particles, like in vegetable-based soups, this must be a part of the calculation process. At Tetra Pak, we have developed a calculation tool, PartCalc, that ensures these calculations are performed with the highest accuracy to achieve the right amount of heat while minimizing any chance of over-processing. 

Viscosity – go with the flow

As mentioned earlier, products under the prepared foods umbrella can have a large range of desired viscosities. The thickness or stickiness of a given liquid impacts how it behaves during heat treatment, in terms of flow profile and turbulence. When flowing through a pipe, high-viscous prepared foods become less turbulent than those with lower viscosity. However, the heating process will often affect the viscosity of the product. Generally, viscosity is reduced when the temperature is increased, but depending on the product’s ingredients, hot swelling starches or denaturating proteins might cause an increase in viscosity at a certain temperature. Such a thickening of the product is often desirable in order to give the intended product texture, but since viscosity affects the flow profile and pressure drop of the product in the system, it is of the utmost importance to consider these changes when designing the system. This is to ensure that the time the product remains in the holding cell and heat exchanger are enough to achieve the regulated heat treatment applicable to the product, which impacts food safety.

At Tetra Pak, we have proven design tools that calculate heat transfer and pressure drop for all heat exchangers in our portfolio. We also have a wealth of experience in rheology measurements that make sure your product is safe for consumption, has the desired texture and is processed in the most optimal heat exchanger.

How much heat?

Ultra-high-temperature (UHT) processing extends shelf life and renders a product safe for ambient storage and distribution by killing vegetative microbial cells, as well as spores that can later germinate and form living cells. UHT treatment is common in prepared food applications, but the choice of temperature and time depends on the product’s intended characteristics.

Fresh, high-quality prepared foods (often desserts) are generally not treated with UHT. They, therefore, have a shorter shelf life and must be stored at cold temperatures. Additionally, products with a high acidic content (low pH), like tomato and fruit preparations, do not generally require high heat treatment because their high acidity inhibits bacterial growth.

For most prepared food applications, Tetra Pak promotes continuous production at UHT temperatures with quick heating and cooling, and a precisely calculated holding time. UHT treatment can be applied to products that are high and low viscous, smooth or particulate –with both large and small particles. All this is made possible by the breadth of the Tetra Pak prepared food heating portfolio, which encompasses everything from plate and tubular heat exchangers to coiled tubular and scraped-surface varieties. A wide selection of batch-heating options are also available, either in combination with pressure cooking or high-shear mixing.

Our extensive product selection, technological expertise and powerful calculation tools make us the ideal partner for your prepared food heating needs.