Introduction

Therefore it is necessary to apply successively several methods, each being chosen with respect to the properties of the material processed at each individual process step, while taking into account both product quality and economy.

Two main water removal processes used in milk powder industry are:

• vacuum evaporation which removes the first part of water and transforms a thin liquid into relatively high viscous milk concentrate, and
• spray drying which transforms the concentrate into powder by atomization and dispersion of small droplets into a flow of hot air. This air supplies the heat necessary for evaporation of water from the droplets and carries away the water vapour.

These two main processes can be further supplemented by:

• membrane processes (reverse osmosis) are, in some cases, suitable for removing the very first portions of water prior to transportation and further evaporation possibly also removing some monovalent salts (nanofiltration). The concentration of high molecular substances like whey proteins is interesting, but not dealt with in this book.
• fluid bed drying which is used for removing the very last portions of water, i.e. transforming the moist powder leaving the spray dryer into a final dry powder. Modern spray dryers are often equipped with an integrated fluid bed in the bottom of the chamber, for either final after drying/ cooling or for intermediate drying followed by a second fluid bed.

The technology of milk powder manufacture is very complex. There are a vast number of different products and compositions, and each product can be produced according to various quality requirements. Moreover there are a great number of qualitative criteria defining not only the composition and overall quality from the general hygiene and health hazard point of view, but also optimum suitability for a given application - so-called functionality.

As with every industrial production, occasionally some irregularities may occur which become evident as abnormal behaviour of the plant. Such behaviour often occurs without any obvious reason, i.e. without any apparent deviation of the production line set-up or operational parameters. The consequence of that may be lack of capacity, excessive loss of product, high consumption of energy, product quality degradation etc.

If this occurs it is necessary to mobilize all efforts to find the reasons for the problems, to solve them and to re-establish regular operation conditions, i.e. to conduct a troubleshooting operation. The objective of this book is to provide for a milk powder technologist the guidelines for trouble-shooting actions. However one cannot discuss trouble-shooting without knowledge of the fundamentals of evaporation and spray drying and the principles of milk powder manufacturing technology. Even well established and well controlled milk powder production facilities cannot fully avoid some production irregularities. An appreciation of basic principles can, to a great extent, reduce their occurrence, and moreover provide means to facilitate the trouble-shooting action. Therefore this book draws the attention to these aspects.

Even if this book is focusing on dairy products, the principles described herein covevering equipment and processes may be used as well in drying other products whether food, chemical or pharmaceutical.