Moving products around during processing is an inherent need for most dairy product manufacturers. The texture and viscosity of products are not only important quality parameters, but also influence how products behave during production and processing. Therefore, they should also be an important influence on the choice of handling and treatment equipment used in the manufacturing process.

The exact requirements tend to fall into two types: those that can be pumped and transported in pipes (such as milk, cream and yogurt) and those that need to conveyed, usually by mechanical belts or similar systems (for example, solid packs of butter and ice cream).

Problems can arise because the pumps used have not been specifically designed for the application or conditions in which they are being used. It is also worth remembering that it is not just simple liquids that can be pumped. With the right equipment, a range of products, including powders, pastes and mixtures of liquids and solids (such as fruit puree), can also be pumped through suitable pipework and equipment. There are a number of advantages to this approach — in particular, the ability to avoid contamination of products during processing, as well as being able to maintain processing temperatures, viscosity, etc.

Assessing difficult products

One of the issues with pumping is the potential to damage products. This is particularly important when handling high-value viscous products such as honey, thick sauces and creams, where any losses can be financially damaging.

The viscosity of different fluids can be affected, resulting in issues such as runny or separated sauces or unwanted churning of dairy products. For materials containing solids — for example, fruit mixtures — the wrong type of pump can easily damage the solid fraction, reducing quality or, at worst, removing the very aspect of your product that you are trying to preserve.

The temperature of the product is important as physical properties will vary with temperature. Viscosity is an important consideration, too, and information on particle size is also required. The chemical composition — for example, is the material acidic? — will also need to be known so that the most cost-effective materials can be used to produce the pump.

As viscosity is a key part of the texture of food and drink, processing operations should not have an adverse effect on it. Factors such as pumping, heating, cooling and passing through pipework all have the potential to affect viscosity, with the exact effects depending both on the liquid itself and the way it is handled.

Benefits of positive-displacement pumps

As well as being designed to handle your product, the pump chosen needs to fulfill the normal requirements of food-handling equipment, including clean-in-place and sterilize-in-place operations. Depending on the range of products handled and product complexity, such operations may be required several times a day between production batches.

Centrifugal pumps are typically used for materials such as batters, oils and beverages, while common uses for positive-displacement pumps include fruit fillings, sauces, cream, cheese and many more. More recently, new purpose-designed reciprocating positive-displacement pumps have been developed to handle very delicate and viscous foodstuffs without damage while working at high pressure in heavy-duty applications in the food and pharmaceutical industries.

Positive-displacement pumps have an expanding cavity on the suction side of the pump and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and is forced out of the discharge side as the cavity collapses.

These pumps feature a sanitary design that incorporates a separator fitted between the piston and the hydraulic chamber to ensure there is no contact between the product chamber and the hydraulic oil. Once the pump is in operation, no part that comes into contact with oil comes into contact with the product.

With a wide range of adjustable flow rates and high pressure drops (up to 435 psi), positive-displacement pumps are suitable for a wide range of high-viscosity, shear-sensitive and large particle-containing fluids, including creams, custards and fruit mixes. Models with clap valves allow pumping of whole fruits, and alternative piston pumps with pneumatic cylinders can be supplied for low-pressure applications.

Whatever foodstuff you are looking to pump, understanding its viscosity properties is the first step to specifying a system that will not result in adverse effects on the quality of your product. The good news is that the processing and packaging part of the food chain is already the most efficient, accounting for just 4% of overall food losses globally, according to “Reducing Food Loss and Waste,” a World Resources Institute publication. However, there is always room for improvement and management processes and equipment design are the two biggest tools food manufactures have at their disposal.