Hydrated Lime

March 19, 2005                                                                                                                                                                                                    ISSUE #159

Dan Vincent's patent on adding hydrated lime [calcium hydroxide, Ca(OH)2] to orange peel issued in 1940. This was a key piece of technology that revolutionized the citrus feedmill industry. The patent describes how lime will react with citrus peel, causing it to release bound moisture. This, in turn, allows a screw press to become an effective machine for dewatering citrus waste.

Over the years, we tried adding lime to a variety of other materials, with negligible results. Somehow, the chemistry was not the same.

It was not until 2000 that lime was added to coffee pulp. (This pulp is the soft tissue on the outside of the coffee bean.) It proved remarkably effective. After the pulp reacts with the lime, a screw press can separate about a third of the mass as a liquid.

In 2003, projects were undertaken to dewater onion waste. Initial efforts focused on developing a shredder that would not jam on the parchment. This was achieved with the scissors action Series VCS machines. With proper shredders, a screw press separated half of the waste as a liquid.

Noting the acid nature of the onion, we tried adding 1% by weight hydrated lime. It worked just as well as it does on citrus waste and coffee pulp. After the onionskin was reacted with the lime, the screw press separated two-thirds of the mass as a liquid fraction.

This testing was done at Gills Onions in Oxnard, California. Gene Ruhnke, our sales rep, noted that there is a Smuckers strawberry plant only a few blocks away. We checked the pH, and it was quite low. Sure enough, lime addition tremendously improved the dewatering of strawberry waste.

The test is simple. Place samples of the material in two plastic bags. Add a tiny amount of the hydrated lime and a little water to one of the bags. (Horticultural hydrated lime from the garden shop will do.) Massage the bags for five minutes. Then squeeze the samples to see if there is a difference in the amount of water that separates.