Water’s impact on fountain beverages and beverage systems: Part three

Nov. 1, 2013

Expert discusses water quality’s effect on ice machines.

No fountain beverage program is complete without ice. In the U.S. there are well over a half million restaurants and nearly all of them have at least one ice machine. Since ice is 100 percent water and such a key component of foodservice it is good to understand how water impacts both the quality of the ice as well as the performance of the ice machine.

In commercial foodservice there are three types of ice machines: Cube, flake and chewable. Cube ice machines can use water-cooled condensers, air-cooled or remote air-cooled. Remote air-cooled is where the condenser is outside the restaurant, usually on the roof. In all ice machines, water fills a sump, where it is pumped through a distribution tube at the top of an evaporator plate. Refrigerant removes the heat from the water as it is cascaded over the freezing evaporator plate and forms into cubes (evaporators can be either horizontal or vertical). Water that doesn’t freeze returns to the sump and is recirculated again. During the harvest cycle, warm water flows over the evaporator plate, dislodging the ice cubes and dropping them into the ice bin.

With flake ice, water flows to a sump and is drawn to an evaporator chamber or cylinder drum surrounded by refrigerant tubing. Ice forms on the evaporator walls, where a screw-shaped auger scrapes the ice off. The ice has more air and, therefore, is less dense, so it is about 20-25 percent softer than cube ice. Chewable ice is formed using a similar process as flake, but the ice is compressed into cylindrical ice “nuggets.” They actually have less liquid and more air than flake ice so they are even softer and easier to chew.

How water affects the quality of the ice

Before we discuss how the tap water affects the equipment, let’s look at how water contaminants affect the ice itself:

  • Hard water causes ice to be cloudy. This is because the dissolved calcium and magnesium solidify into particles during the freezing process and become trapped in the ice.
  • High total dissolved solids (TDS) can cause misshapen ice, resulting in freeze-up and/or bridging in the machine (more on this later).
  • Water high in dissolved sodium can cause soft, fast melting cubes.
  • High iron can promote slime buildup inside machine and bin. This is because there are iron bacteria that feed and multiply on ferrous (dissolved) iron. A byproduct of these bacteria is slime. This slime is not only unappealing and gets onto the ice, but it can also cause corrosion (more on this later).
  • Chlorine can give ice a “swimming pool” taste and odor. While some of the chlorine will gas off during the freeze process on the evaporator plate, some will become trapped in the cube. As the ice melts in the drink, the chlorine is released.
  • Organics affect taste, odor and color. Tannins, for example, result from the natural breakdown of decaying vegetation and cause yellow/brown tones. They can impart an astringent and “earthy” taste.

How water affects cube ice machines

Most water-related problems with ice machines and ice quality are caused by TDS, the mineral content of the water which can include carbonates, chlorides or both. Hard minerals, such as calcium and magnesium, when the alkalinity is favorable, leave scale deposits. Scale causes a number of problems with cubers:

  • Scale on the ice thickness probe can trigger a false harvest. If it can’t sense the water, it may start the harvest cycle prematurely, releasing the ice before it is fully shaped.
  • Scale can cause “freeze up,” a fairly common problem. As minerals collect on the evaporator plate, they can impede the heat transfer. This can result in ice that sticks to the evaporator instead of dropping during the harvest. The ice refreezes with each cycle, creating large chunks.
  • Scale can cause valves and floats to stick:
    • An inlet valve or float that is stuck partially closed can result in a longer harvest cycle and unusually large cubes. Low water flow can also lead to small cubes. If the valve is stuck completely closed, it would activate the low water safety and stop ice production. (Note: Low water flow can also be due to an inlet screen that is plugged with debris.)
    • A valve that is stuck open can cause leaking and overfilling of the reservoir or sump. This can cause three problems:
      • The water temperature can be tempered to the point that ice can’t be formed.
      • Freeze up and bridging of cubes:
        • Low water flow caused by a stuck valve can cause freeze up, in which the ice stays attached to the evaporator plate during harvest.
        • Excessive water in the reservoir, due to a valve stuck open, can release too much water during the freeze cycle, building excessive layers of ice that “bridge” together. When released, the cubes don’t break apart in the bin, but instead remain as large chunks.
      • A valve stuck open can also result in a lot of water waste.
  • Water distribution tubes can clog due to scale. This can lead to ice bridging on some portions of the evaporator plate and no ice on other portions.
  • A stuck bin control due to scale can send a false signal that the bin is full, stopping ice production.

Another problem is corrosion. Corrosion due to water primarily comes from chlorides, although there are other sources such as chlorine and slime. Chloride ions can enter water through mineral deposits of sodium chloride, potassium chloride and calcium chloride, which easily dissolve in water. Chlorides cause pitting in stainless steel by breaking down the passive oxide layer. This layer naturally forms when the elements react with oxygen in air or water. This protective film helps to give stainless steel its resistance to rust. Once this layer is compromised, a pit is formed. Once corrosion forms future corrosion is focused in the pit, causing it to grow until it bores through the metal and/or causes a stress crack.

Bacteria and slime, as mentioned, are common issues in ice machines. Ice machines and bins should be cleaned per the manufacturer’s recommendations and sanitized in accordance with FDA regulations. In certain environments, the ice machine may require more frequent cleaning, such as areas that have yeast in the air (for example bakeries and micro-breweries).

Bacteria can enter an ice machine in three ways: Through the water, by air or by touch as ice is removed from the bin. The bacteria feed on organic material and begin to colonize, producing a byproduct of polymer biofilm, or slime. (Note that bacteria adhere better to rough surfaces, such as surfaces that have mineral scale deposits.) This slime can cause fouling inside the machine and detach and fall onto the ice. Slime can also contribute to corrosion, especially when the biofilm is produced by bacteria feeding on iron and manganese and causing oxidation. In addition, slime can plug the sump drain, causing overfilling.

How water affects flake/chewable ice machines

Many of the issues described above apply to flake machines as well. However, due to the different method of producing ice, there are a few problems unique to these types of machines:

  • When scale builds up on the evaporator cylinder, it insulates the freezing surface. This prevents heat transfer, causing the ice to come out of the extruding head wet. This can put extra stress on the gear motor from rotating the auger for extrusion. This not only can make a lot of noise, but it can also cause the motor to wear prematurely. It could increase the running amperage, activating the overload reset on the motor and shutting the machine down.
  • A softer/wet flake is more likely to bridge in the ice bin.
  • Scale and dirt that collects on the bearings can affect the auger movement. The space between the auger and the evaporator is very tight, so if the auger is off kilter, it can scrape the cylinder, damaging the auger blades.

Treating water for ice

With ice machines you want to remove the dirt and particulate that can clog screens and holes, cause abrasion on the augers and extruders in flake/nugget machines and affect the appearance of the cubes. You also want to remove the chlorine and chloramines that can affect the taste and smell of the ice and can contribute to corrosion (unless slime is a problem, then you may want to consider a carbonless filter, more on this later). You also want to lower the TDS or use a scale inhibitor to prevent scale deposits on the evaporator plate, probes, solenoids and floats.

Reducing the dirt and particulate can be achieved with an inexpensive coarse pre-filter. For water that is extremely high in particulate there are industrial-grade pre-filters and self-cleaning hollow fiber ultrafiltration systems available.

Carbon filtration is excellent at reducing chlorine. For chloramines (a compound of chlorine and ammonia that many municipalities are switching to) a special catalytic carbon is required. There are a number of chloramine-reducing systems on the market to address chloramines.

For scale control, a water filter with polyphosphate is a low cost solution. The phosphate prevents scale by keeping most of the dissolved calcium and magnesium mineral from nucleating on dirt particles and falling out of the solution. Instead, the mineral passes harmlessly through the ice machine. For areas with very high TDS, a reverse osmosis (RO) system with blend capability and a storage tank are best.

The definition of “high” TDS will vary depending on the composition of the dissolved mineral. For example, a TDS of 500 ppm composed primarily of sodium chloride is more detrimental to ice and equipment than a TDS of 500 ppm composed mostly of calcium bicarbonate because the sodium will cause mushy ice and corrosion. The blend capability on the RO system means that the system can blend filtered water (that contains TDS) with the pure permeate water, diluting the TDS to approximately 250 ppm or less. You do not want to use pure RO water with ice because the low pH will lead to corrosion on metals and poor tasting ice (remember that hard mineral helps to give water its flavor). An additional note regarding RO: A brine water softener should not be used directly on an ice machine because the added sodium leads to soft, fast melting ice. A softener could feed an RO system because the sodium would be removed during the RO process. By feeding the RO system with softened water, the production of pure water is increased and the RO membrane will last longer.

There are a number of products on the market for preventing bacteria and slime growth in ice machines and bins, including silver-coated ceramic pellets, UV and ozone. Another method is to treat the water for particulate, but allow chlorine or chloramine to pass through the ice machine. There are water filters on the market that are carbonless, but still remove particulate and provide scale inhibition.

With the growing popularity of iced coffees, sweetened iced teas, bubble (“milk”) teas and artisan sodas in foodservice, the demand for ice is higher than ever. Keeping the ice machine running at peak efficiency with the right water treatment will reduce operating costs and prevent downtime (and lost revenue). A secondary benefit is hard, crystal clear cubes with no off-flavors. A good water filter system is a small investment when compared to the cost of an ice machine and it will pay for itself in reduced ice machine headaches.

Roy Parker is the global senior marketing manager for the foodservice vertical of Pentair, which includes the product lines Everpure® and Shurflo®. He’s been with Pentair for seven years and is based at the foodservice World Headquarters in Hanover Park, Illinois. He can be reached at [email protected]. Pentair Everpure is celebrating 80 years and Pentair Shurflo is celebrating 45 years of providing innovative water treatment and beverage system solutions for foodservice operations around the world.

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