Live steam is used to process a large number of foods. Equipment to generate steam and use it for industrial purposes has existed since at least the middle of the 18th Century. Efficient use of steam to prepare food beyond household scale was documented by the early 19th century. While fuels, metallurgy, control systems, and maintenance programs have changed since that time, the fundamental scientific principles, basic designs, and problems associated with those systems have remained constant. (reference)
Steam, historically, has been a vital part of the food processing industry. It is used, both directly and indirectly, for heating, cooking, sanitizing, and sterilizing. The advent of the industrial revolution provided the impetus for the large scale processing of food. Steam was the medium which allowed this to happen. It was easy to produce and simple to transport to points of use. Because of this ease and simplicity steam was taken for granted and no thought was given to improving the ways in which steam was used or of alternatives to the use of steam. Through the years, fuel costs were low and the systems that were in place did the job satisfactorily. The production of superheated water under pressure suitable for direct food contact called ‘culinary steam’ requires food-grade equipment, clean water, and sanitary conditions where food contact is a possibility. Food processors have fewer options in metals, water treatments, fuels, and other aspects of steam generation and boiler operations than those who operate boilers for non-food uses, such as electric power generation. (Reference 37)
Typical problems that occur with steam equipment are pitting, deposition of insoluble compounds (scale), and corrosion. This damage is mitigated through system design, selection of suitable fabrication materials, process control, and the use of controlled dosages of particular substances that prevent or reduce these problems.
Pitting is generally caused by the impact of solids against the sides of a boiler. The best solution for this is the filtration of water to remove such solids. Some filters may use chelating agents to attract and retain solids through chemical reaction. Scale is a coating of thermally non-conducting solids on the waterside of a boiler, usually composed mainly of precipitated calcium carbonate (CaCO3). This frequently is the result of water that has a high mineral content, known as ‘hard’ water.
Water can be treated a number of ways before being fed into a boiler to remove calcium and other minerals responsible for scaling. Filtration, activated carbon, ion exchange, and reverse osmosis (RO) are all used by food processors to remove undesirable particles and chemicals from water. Water can be deionized by filtration with either natural or synthetic substances. Various colloids and chelating agents can also remove minerals from feedwater.
Water may also be chemically treated to prevent scale. Among these are sodium phosphates, lignin sulfonates, sodium hydroxide, and sodium silicate. These compounds can usually be reduced to acceptable levels by precipitation, filters, or traps.