The quality of the water used for bakery and food processing has been of increasing interest over the last few years. Previously, when owners would inquire about using chillers for their bakery or snack business operation, the driving motivation was a chiller’s ability to provide a consistent temperature. (Often, they were looking to switch from using ice to cool their ingredients.) They were not as concerned about filtering out lead, pathogens or poor taste from the water they used in their ingredient mixes. A typical response was, “They like the taste of our products. Why do I need to change it?”
But, when a large national pizza company wanted to make a change in their ingredient chilling process, their engineers had more stringent requirements. The company’s goals were to ensure that its products were safe and of consistently high quality. The chilled water used in their ingredient mixes had to be free of contaminants (bugs). To make sure this would happen, the company installed valves to shut off the water going to their mix lines if a UV sterilizer bulb went out in the purification unit on the makeup water line. This way, they knew the water going in the mixers was always going to be safe and of the highest quality.
The pizza company employs an inline filtration unit that uses a three-stage water purification system on the makeup water going to the ingredient water chiller. The process to filter the water for the pizza dough starts with particulate filters and carbon purifiers before flowing through the UV sterilizer to remove disease-causing bacteria, viruses and microorganisms. This is the same filtration process used for drinking water applications around the world.
The application is long proven: During World War II, the U.S. Army contacted one chilled water equipment manufacturer for a solution to produce filtered and cold water for the food services at the U.S. Army field camps. Particularly in hot locations such as the desert, food services wanted to have more control over the temperature of their dough mixes. During high ambient conditions, the yeast in a dough mix would activate too quickly, causing the dough to rise too early. Also, there was no way to be sure that the ingredient water would be safe.
Working closely with U.S. Army engineers, the chilled water equipment manufacturer designed a batch-type ingredient water chiller for government bakeries. Taking advantage of its storage method of cooling, the chilled water equipment manufacturer designed a water chiller that, at the push of a button, could supply batches of consistent 34°F (1°C) water into a dough mixer without danger of freezeup. The chiller included a water purifier so that bread for the troops was mixed with purified water.
How does the batch draw chiller work? The chillers are specially designed with a high transfer immersion coil evaporator and large holdover storage to supply ingredient water at 34°F (1°C) and to maintain temperature setting within ± 1.5°F (0.8°C). This important storage feature provides a large volume of chilled water for the dough and acts as a refrigeration “cushion.” This means the stored water volume helps prevent overload and short cycling that is common to chillers without storage.
Sometimes, a multi-stage purification system is best for the application (table 1). When considering the stages of ingredient water purification, there are a few considerations. For the first stage of the water filtration, the particulate filters act as prefilters to remove sediment and other suspended particles from the water using cartridges made from thermally bonded microfibers of polypropylene. The graded-depth construction is made up of fibers that are wound more tightly toward the core of the cartridge. Consequently, the entire depth of the filter element is used for more effective filtration and longer service life. The filter improves the clarity of the water and extends the life of the purifier.
In one chilled water equipment manufacturer’s equipment, the second-stage carbon elements qualify for the NSF/ANSI Standard 42 for removal of sediment down to 5.0 microns as well as organic or chlorine taste or odors. The carbon block — a naturally occurring material — is biodegradable and is replaced easily.
Both the particulate and carbon elements are cut to size. The length and amount of elements are related directly to the flow rate: The higher the flow rate, the more elements are required. The filter and purifier housings are constructed of heavy-duty stainless steel and are rated at 120 psi working pressure.
For extra purification, a third-stage UV water sterilizer is added. One chilled water manufacturer’s equipment has a germicidal that eliminates microorganisms that can cause waterborne diseases without the use of chemicals or toxic products. Operation is low cost because the energy consumption is equal to ordinary fluorescent tubes.
UV radiation, with a wavelength of 2,536 angstroms, is produced from a low pressure mercury lamp. The lamp is encased in a high purity quartz sleeve that is immersed in water inside the stainless steel sterilizing chamber. The chamber is removed as a bundle for inspection or cleaning. By regulating the flow of water through this chamber, disease-causing microorganisms such as bacteria, algae, spores and viruses are exposed to a dose of at least 40,000 µw-sec/cm2 (table 2).
How does this filtration system work with the chiller? City water is sent to the particulate filter, where suspended particles from 0.5 to 20 microns, depending on the filter used, are removed from the water. The water then flows to a purifier to remove poor taste and unwanted odors. Both filter and purifier elements are housed in stainless steel filter canisters. The sizes and the number of filters, purifiers and UV sterilizers are determined by the user’s water requirements.
The final stage of water filtration is the UV sterilizer system to eliminate the bacteria and other contaminants from the water (table 2). The differential pressure switch (DPS) monitors the filter elements and sets off a light when the filter or purifier needs to be changed. The air vents prevent air locks and ensure that the filters operate properly. The flow regulator controls the flow rate of the water entering the UV sterilizer chamber. This is important because the exposure time the water has to the UV will determine what germs and microorganisms are killed. The treated water is sent to the chiller where it is cooled before mixing with the ingredients.
The combination of storage-type chiller and water filtration system allows for better control of taste and consistency of the product for food processing and other applications.