Why do we put food stuff in liquid to then dry it again?
Karl-Heinz Bahr: “For various reasons, but mostly to produce food particles with consistent properties, and to improve the quality of the product, for example by adding vitamins or minerals prior to drying. Many of those dried food products are intended to be dissolved prior to consumption, like milk powder. And of course, after you dry a product, you don’t need to transport the water, so this typically reduces the weight of the product by 70-80%. Transporting dried products is therefore less expensive and better for the environment. Also, the (microbial) stability is much higher in dried products."
How to get the hygienic dryer that's best suited to our needs?
“By defining your requirements as clearly as possible. Start off with your product and user requirement specifications. Every detail is equally important: the kind and type of end product you want to produce, the look and feel, the smell and taste. The viscosity and transition temperatures of your product matter, as well as the droplet size required to produce your dry material particles. And let's not forget about the rheology of your product - it determines the shape and size of the spray nozzles. Furthermore, you have to think about the needed pressure, the temperature, the amount of air, and even the shape of the spray dryer. Some people think that all dryers are the same, but dryers come in various shapes. Also the liquid can be prepared in various ways, so it is not only the spray dryer itself that matters. That's why the building design and the utilities should be considered as integral parts of the process. The environment has a big influence on the product as well, not only in relation to energy consumption - it also needs to be hygienic and, most importantly, as dry as possible to avoid microbiological issues. The goal is to realise consistent and effective drying processes without wasting resources. Even big food companies cannot do this alone. They seek support from experienced system integrators. To a layman's eyes, spray and fluid dryers may not look very sophisticated, but they are in fact very delicate thermo-energetic systems.”
Why is that?
“The temperature, pressure and energy balances within the installations determine their effectiveness and the quality of the product. Spray dryer and fluid bed dryer installations are very prone to the slightest fluctuations in temperature, pressure levels, the quality and quantity of the drying air and so on. Therefore, when designing and configuring spray dryer and fluid bed dryer installations, it’s always a challenge to find the best possible balance between the productivity, the water and energy consumption and of course the food safety and quality aspects. You can imagine that to reach this balance, you need a top-class team of suppliers and operators."
Sounds like a lot of work. Time consuming? Expensive?
"Spray dryers are not cheap, so you need to do your homework before making investment choices. If you want to educate yourself, the newly updated EHEDG Guideline Document 31 Hygienic Engineering of Spray Dryer and Fluid Bed Plants is certainly a good place to start, since this guideline contains a comprehensive oversight of many hygienic engineering and design principles applicable in spray dryer and fluid bed plants, not only related to the equipment but also for the environment it is placed in. The guideline is developed by experts of the EHEDG Working Group Dry Material Handling. Many details of the process and the environment are thoroughly discussed and related to specific design choices. Because even when you work with an experienced system integrator, you are always better off when you are aware of some of the details that you need to pay attention to. This helps you to make sure you have a hygienically sound spray or fluid bed drying installation in place."
What are the most common mistakes?
“We have to make a clear distinction between operational and process line design mistakes. First of all, people tend to underestimate the effects of a lack of control over the system process variables, for example when using unconditioned airflows. When the humidity of the air outside of the plant changes, it can affect the system in unexpected ways, resulting in fluctuating product quality or material deposition on the inner walls of the drying chamber, ducting, cyclones and product transport lines. A general rule of thumb is that better hygienic design dryers allow for more inconsistencies in these variables without immediately compromising on food safety and food quality. However, to really optimise food safety in spray dryer and fluid bed dryer plants, one has to look at the system and the environment as a whole: as a combination of design and usage aspects. The process is the product.”
The process is the product?
“Yes, because with most dry particle food products, taking samples for product release purposes doesn’t make much sense, since it’s impossible to take a representative sample. This is particularly true for microbiological testing. In a powder product, only one square centimeter in a full batch could be contaminated while the rest is fine. That means that besides a trustworthy hygienic design of your installation, you need very strictly supervened cleaning procedures and operating instructions and a top-class team to run, clean and maintain the installation. Hygienic engineering and design can definitely minimise contamination risks, but only if all food safety determining variables are fully controlled.”
Thanks for your clear answers.