Different Types of Evaporators Used in the Food Industry

Concentrated orange juice, powdered milk, tomato paste – these everyday food products all rely on one critical processing step: evaporation. In simple terms, evaporation removes water from liquid food products to create concentrated versions with longer shelf life, reduced weight, and lower transportation costs. But the type of evaporator you use matters – a lot. Different food products have different viscosities, heat sensitivities, and concentration requirements, and picking the wrong evaporator can ruin product quality or waste energy. This post breaks down the main types of evaporators used in the food industry and explains when each one makes the most sense.

What is an evaporator and why does it matter in food processing? 🔗

An evaporator is essentially a heat exchanger designed to boil off water (or another solvent) from a liquid food product, leaving behind a more concentrated solution. The system typically has three core components: a heat exchanger to transfer thermal energy, a separator to divide the vapor from the remaining liquid, and a condenser to cool and collect the vapor.

In the food industry, evaporation is one of the most common unit operations. It improves microbial stability by lowering water activity, reduces mass and volume for easier storage and transport, and prepares products for further processing steps like drying or crystallization. Applications include concentrating fruit juices, milk, coffee extracts, sugar solutions, and vegetable pulps.

However, evaporation is an energy-intensive process. That is why evaporator design must balance heat efficiency with product quality – especially for heat-sensitive foods like dairy and fruit juices, where excessive heat exposure causes nutrient loss, off-flavors, or color changes. The choice of evaporator depends on several factors: the product’s viscosity, its sensitivity to heat, the desired final concentration, and the risk of fouling or scaling on heating surfaces.

Batch-type pan evaporators 🔗

The batch-type pan evaporator is the simplest and oldest type of evaporator used in food processing. It consists of a steam-jacketed spherical or hemispherical vessel where the food product is heated. The vessel can be open to the atmosphere or connected to a condenser and vacuum system for lower-temperature processing.

How it works 🔗

The liquid food product is placed inside the pan and heated using steam that circulates through the jacket surrounding the vessel. As the product heats up, water evaporates from the surface. The process continues until the desired concentration is reached, and then the batch is discharged. The heat transfer area per unit volume is relatively small in these evaporators, which means residence times are typically several hours.

Advantages and limitations 🔗

Batch pan evaporators are mechanically straightforward, inexpensive to build, and easy to operate. They work well for small-scale production where the product must be handled gently – for instance, concentrating jams and jellies where whole fruit pieces are present. They were also historically used for corn syrup concentration until the early 1960s.

The main drawback is the long processing time. Because the product sits in the heated vessel for hours, heat-sensitive foods can degrade significantly. To counter this, processors often run batch pans under high vacuum to lower the boiling point and reduce thermal damage. Still, for most modern food processing operations, batch pan evaporators have been replaced by continuous systems that offer better efficiency and product quality.

Natural circulation evaporators 🔗

Natural circulation evaporators represent a step up in efficiency from batch pans. These units use the principle of thermosiphon circulation – the natural tendency of heated liquid to rise and cooler liquid to descend – to move the product through the heating tubes without any mechanical pump.

How it works 🔗

In a typical design, short vertical tubes (usually 1-2 meters long and 50-100 mm in diameter) are arranged inside a steam chest positioned at the bottom of the vessel. As the product inside the tubes is heated by steam condensing on the outside, it naturally rises through the tubes due to the density difference between the heated liquid and the cooler liquid surrounding it. The product circulates continuously as long as heat is applied, and vapor separates at the top of the unit.

Applications in food processing 🔗

Natural circulation evaporators are suitable for products with relatively low viscosity and minimal fouling tendency. They are commonly used in sugar beet processing, caustic concentration, and for handling foamy liquors. In food processing, they serve as a reliable option for straightforward concentration tasks where extremely short residence times are not critical.

The key advantage here is simplicity – no pump is needed, which reduces both capital costs and maintenance requirements. However, circulation rates are lower compared to forced-circulation systems, and the evaporator does not handle viscous products well because the natural driving force may not be sufficient to maintain adequate flow.

Rising-film evaporators 🔗

Rising-film evaporators are considered one of the first “modern” evaporator designs, dating back to the early 1900s. They are essentially vertical shell-and-tube heat exchangers where the liquid feed enters from the bottom of long vertical tubes and is heated by steam on the shell side.

How it works 🔗

As the liquid inside the tubes heats up, it begins to boil, generating vapor in the centre of each tube. This vapor creates an upward pressure that pushes the liquid against the tube walls, forming a thin ascending film. The higher the vapor velocity at the centre, the thinner the liquid film becomes. This thin film provides excellent heat transfer because there is a large surface area in contact with the heated tube wall relative to the volume of liquid.

At the top of the tubes, the mixture of concentrated liquid and vapor enters a separator, where the two phases are split. The concentrated product is collected, and the vapor moves on to a condenser or to the next effect in a multiple-effect system.

Advantages 🔗

The biggest advantage of rising-film evaporators is their short residence time. The liquid moves quickly through the tubes, minimizing heat exposure. This makes them suitable for concentrating heat-sensitive products like fruit juices, milk, and other dairy items. They also offer relatively high heat transfer coefficients, which means less heat transfer area is needed, lowering capital costs. Additionally, continuous operation is possible, improving energy and time efficiency over batch processes.

Limitations 🔗

Rising-film evaporators work best with low-viscosity liquids that have minimal fouling tendencies. They require a sufficient temperature difference between the steam and the product to generate enough vapor pressure to drive the upward film movement. For highly viscous or particle-laden products, this design can struggle. In recent decades, falling-film evaporators have increasingly replaced rising-film units for many food applications due to their superior efficiency and gentler handling of sensitive products.

Falling-film evaporators 🔗

The falling-film evaporator is arguably the most widely used evaporator type in modern food processing. It works on the opposite principle of the rising-film unit – liquid is distributed at the top of vertical tubes and flows downward as a thin film under the force of gravity.

How it works 🔗

A distribution system at the top of the evaporator ensures that the liquid feed spreads evenly across the inner surface of each tube. As the thin film flows down, steam on the shell side heats it, causing evaporation. The vapor generated travels downward alongside the liquid film, resulting in efficient heat and mass transfer. At the bottom, the vapor-liquid mixture enters a separator where concentrated product and vapor are split apart.

Why the food industry loves them 🔗

Falling-film evaporators excel at handling heat-sensitive products because they operate at lower temperatures and provide very short contact times between the product and the heated surface. According to equipment manufacturers like ANDRITZ, key advantages include shorter residence time for better product quality, lower power consumption, and lower capital expenditure especially at high evaporation rates.

These evaporators are the go-to choice for dairy processing (milk and whey concentration), fruit juice concentration, and pharmaceutical extracts where preserving flavor, color, and nutritional content is critical. They handle low to moderate viscosity products extremely well and can achieve high concentration ratios.

Considerations 🔗

Proper liquid distribution at the top of the tubes is essential – uneven distribution can lead to dry spots on the tube wall, causing localized overheating and product damage. Falling-film evaporators also do not perform well with very high viscosity products or those containing large suspended particles, because the film may not flow evenly. For such challenging products, forced-circulation evaporators are a better fit.

Forced-circulation evaporators 🔗

When the product is highly viscous, prone to fouling, or contains dissolved solids that tend to crystallize, forced-circulation evaporators are the preferred choice. Unlike the previous types, these systems use a mechanical pump to circulate the liquid at high velocity through the heat exchanger tubes.

How it works 🔗

The liquid is pumped from the bottom of a separator vessel through external heat exchanger tubes, where it is heated by steam. A key design feature: boiling does not occur inside the tubes. Instead, the liquid is superheated under pressure as it passes through the heat exchanger. When the heated liquid enters the separator (which operates at a slightly lower pressure), it undergoes flash evaporation – the sudden pressure drop causes rapid vaporization. The vapor exits from the top of the separator, while the concentrated liquid is either recirculated through the system or withdrawn as product.

The high flow velocity through the tubes (typically 1.5-4 m/s) prevents deposits from forming on the heating surfaces, which is why forced-circulation evaporators handle fouling-prone and crystallizing solutions so effectively.

Applications in food processing 🔗

Forced-circulation evaporators are widely used for processing products like fruit and vegetable purées, tomato paste, and mango pulp – products with high solid content and high viscosity. They are also common in sugar refining and corn steep water concentration. In many food processing plants, a forced-circulation evaporator is used as the final concentration stage after a falling-film evaporator has done the initial water removal, since falling-film units struggle at very high solid concentrations.

Advantages 🔗

The primary strengths of forced-circulation evaporators are their ability to handle difficult products (viscous, scaling, crystal-forming), their high heat transfer rates due to turbulent flow, and the fact that no boiling occurs on the heating surfaces – which dramatically reduces fouling. They also offer precise control over product temperature and concentration. GEA notes that because evaporation happens in the separator rather than on the heating surface, fouling from incrustation and precipitation is minimized, allowing for longer operating periods between cleanings.

Limitations 🔗

The mechanical pump increases both capital and operating costs compared to natural or film-type evaporators. Energy consumption is also higher because the pump must continuously drive the liquid at high velocities. For low-viscosity, non-fouling products, a falling-film evaporator will almost always be more economical and efficient.

Choosing the right evaporator: key factors 🔗

No single evaporator type works best for every food product. The selection depends on a combination of product characteristics and processing requirements:

Product viscosity is one of the most important factors. Low-viscosity liquids like fruit juices and milk are well suited to falling-film or rising-film evaporators. High-viscosity products like tomato paste or fruit purées typically require forced-circulation systems.

Heat sensitivity determines how much thermal exposure a product can tolerate. Dairy products, juices, and pharmaceutical extracts need short residence times and low processing temperatures – falling-film evaporators are ideal here. Batch pan evaporators, with their long residence times, are only suitable when the product can withstand extended heating.

Fouling and scaling tendency matters for products with high dissolved solid content or those prone to crystallization. Forced-circulation evaporators, with their high flow velocities and flash evaporation design, minimize surface deposits and allow longer runs between cleaning cycles.

Final concentration level also plays a role. Some evaporator types handle higher concentration ratios better than others. It is common to see combination systems in large food processing plants – a falling-film evaporator for initial concentration followed by a forced-circulation unit for the final, high-solids stage.

Scale of operation affects economics. Batch pans work for small-scale artisanal production. For industrial-scale processing, continuous systems like falling-film and forced-circulation evaporators are far more efficient in terms of energy use, throughput, and product consistency.

Modern trends in evaporator technology 🔗

The food processing industry is continuously pushing for better energy efficiency and product quality in evaporation. Two technologies stand out in this regard:

Multiple-effect evaporation connects several evaporator units in series. The vapor produced in the first unit serves as the heating medium for the second, and so on. This approach dramatically reduces steam consumption – a three-effect system, for example, uses roughly one-third the steam of a single-effect system for the same amount of water removed. According to research published in ScienceDirect, multiple-effect evaporators combined with vapor recompression systems provide substantial energy savings, making them standard in large-scale food processing.

Mechanical vapor recompression (MVR) takes the vapor produced during evaporation, compresses it to raise its temperature and pressure, and then feeds it back as the heating medium. This essentially recycles the energy within the system, cutting steam consumption by up to 90% compared to a single-effect evaporator. Many modern dairy and juice processing plants use MVR-equipped falling-film evaporators for maximum efficiency.

Advances in automation and real-time process control also allow operators to optimize temperature, pressure, and flow rates dynamically, ensuring consistent product quality while minimizing energy waste.

Quick comparison of evaporator types 🔗

Batch-type pan evaporators: Simple, low cost, suitable for small-scale production of jams and jellies. Long residence time, not ideal for heat-sensitive products.

Natural circulation evaporators: No pump required, low maintenance, suitable for low-viscosity products. Limited circulation rate, not for viscous products.

Rising-film evaporators: Short residence time, high heat transfer, continuous operation. Best for low-viscosity, heat-sensitive products like juices and milk. Less efficient than falling-film designs.

Falling-film evaporators: The industry standard for heat-sensitive foods. Very short contact time, low temperature operation, high energy efficiency. Requires proper liquid distribution; struggles with very viscous products.

Forced-circulation evaporators: Handles viscous, fouling-prone, and crystallizing products. Flash evaporation minimizes surface fouling. Higher capital and energy costs due to the circulation pump.

What do you think? If you were setting up a fruit juice concentrate plant, which evaporator type (or combination of types) would you prioritize – and would energy efficiency or product quality be your primary deciding factor?

References

1. https://www.andritz.com/separation-en/insights/evaporators-guide
2. https://www.slideshare.net/slideshow/evaporation-38794401/38794401
3. https://en.wikipedia.org/wiki/Circulation_evaporator
4. https://en.wikipedia.org/wiki/Rising_film_evaporator
5. https://enggcyclopedia.com/2023/03/rising-film-evaporator/
6. https://www.alfalaval.com/products/process-solutions/evaporation-systems/viscovap/
7. https://www.gea.com/en/products/evaporators-crystallizers/evaporator-plants/forced-circulation-evaporator/
8. https://www.andritz.com/products-en/separation/evaporators-crystallizers/dedert-forced-circulation-evaporators
9. https://www.sciencedirect.com/science/article/abs/pii/B9780128187647000049