The Professor: Hard Ice vs. Soft Ice

June 4, 2012
Ice 1
Homes, restaurants, and businesses rely on clear, clean ice for many applications. Ice is considered a food source, and the water that makes the ice must be of good quality. Good quality water will produce a crystal-clear, hard piece of ice.

Ice hardness is a measure of the thermal cooling capacity (Btus) of the ice. Ice hardness is measured as a percentage. Flake ice falls in the 75 percent hardness range where block ice falls in the 95 to 100 percent hardness range depending on the quality of water making the ice and how the ice is made. The higher the percent of hardness, the more cooling ability or cooling capacity the piece of ice will have. This occurs because hard ice is denser than soft ice. Harder ice will last longer in a glass when cooling a drink or in a cooler cooling food.

However, do not confuse ice hardness with water hardness. Water hardness has to do with the amount of minerals dissolved in the water. The more minerals dissolved in the water, the harder the water. Hard water reduces the ice hardness and its cooling capacity because of the higher mineral content in the ice.

Figure 1 shows the difference between hard and soft ice. The ice sheet on the left in the photo is cloudy and soft. It contains a lot of minerals. The ice sheet on the right is clearer, denser, and will have a higher hardness percentage with more cooling capacity.

Ice Machine Service

Consider this scenario of a typical problem that may occur with an ice machine. A service technician is called to service an ice machine. The restaurant manager says that customers are complaining about how cloudy and white the ice is in their beverages. Customers are also complaining about a fine, white powder in the bottom of their beverage glasses once the ice has melted, and that the ice melts very fast.

The service technician takes the front cover off the ice machine and observes a fine white chalky powder in the water sump (see Figure 2). The technician then places his fingers into the bottom of the water sump and pinches a sample of the white powder (see Figure 3). A closer examination reveals that the fine white powder is concentrated, undissolved mineral buildup in the bottom of the water sump. In fact, a close examination of the ice sheet also reveals this fine white powder spread throughout the sheet.

The service technician then carefully watches the ice machine as it runs through a complete ice making cycle. The inside of the front cover of the ice machine has a complete step-by-step written sequence of events and a wiring schematic for the technician to follow as he reads the sequence of events for the ice machine.

The service technician notices that the water in the ice machine’s sump did not dump out during part of the harvest cycle. Because of this, no new water was allowed to enter the ice machine’s water sump because of a water level sensor being satisfied during the harvest cycle. Further investigation reveals that the water dump solenoid valve is not operating. The inoperable dump solenoid valve prevented the mineral-laden water from being flushed out of the ice machine every cycle. Ideally, if the water velocity and water volume over the evaporator is correct, only water should freeze on the evaporator. However, with the water in the ice maker’s sump being so concentrated with minerals because of an inoperative water dump solenoid, both water and minerals are freezing and causing cloudy, soft ice.

The technician then waits for the next ice harvest cycle and places the probes of his voltmeter on the terminals of the solenoid coil of the water dump solenoid. The technician measures proper voltage to the solenoid coil at the appropriate time during the sequence. The technician then disconnects power to the ice machine, removes a wire from the dump valve’s solenoid coil, and ohms the coil. The service technician reads infinity with an ohmmeter. This proves an open solenoid coil. A new solenoid coil is placed on the water dump valve and then wired. After a thorough cleaning, the ice machine is put back into service. With the water dump valve and new solenoid coil working properly, the first batch of ice is crystal clear and hard.

Publication date: 6/4/2012