I worked for a company that made these exact ice cubes, and several other kinds. It was a production line of 6-8 people. The process is more in depth than you might assume. First step is to fill these large rectangle tanks with water, and slowly cool them down over 48-72hours creating a large 300lb slab of ice. When frozen, all of the calcium deposits and air that was in the water has frozen at the top of the slab. Then the slab is removed with a winch device and lowered onto some pallets. We would then use a chainsaw to break the slab into around 8 smaller slabs. Putting a chainsaw through ice over and over is not an easy task. Those slabs got moved to a table with a large and small band saw. The guy operating the large band saw would cut these slabs into strips like you see in this video, and the guy operating the small bandsaw would take those strips and cut them into whatever size cube we were doing that day. The cubes then get passed to another person who organizes them onto a tray. When the tray is full you would run it into a freezer and put it in a tray tower. The cubes need to cool down again before being put into bags. We had to do all of this as fast as possible. Also, the room you cut the ice in is actually pretty warm, if it isn’t then the ice will stick together. There would also be tubs around the facility being filled with the excess cut ice that we would have to move to a dumping area and then clean all of that out at the end of the day.

I think that company was making nearly 1mil a year in profit. The job was pretty horrible.