Egg crackers make up an industry that not many people are aware of. Their business is to process truckloads of eggs from layer farms into basic food ingredients: egg whites and yolks. These two bulk commodities are sold to food processors who use them as food ingredients. They ship their products in refrigerated tanker trucks containing approximately 5,000 gallons each.
One member of the industry is Daybreak Foods of Minnesota. We visited one of their plants where they have six egg cracking machines. These are contained within the "sanitary" half of their small factory. They crack about 3,000,000 eggs per day.
Banks of suction cups lift the eggs from the shipping cartons. Some cracked and broken eggs are culled by inspectors. Next the eggs are candled: a bright light is shined through the egg to detect internal impurities. This is done to eliminate any fertile eggs containing
blood spots (embryos). Following an automatic wash cycle the eggs are conveyed into the room with the egg cracking machines. These are Lazy Susan type machines that automatically crack the eggs and separate the egg whites (albumen) and yolks into two separate flows.
This factory generates about 18 tons of waste material per day. This waste is mostly eggs shells, but it also includes the cull eggs, the no-cracks from the egg crackers, and other "bad" eggs. This material is sent to a landfill.
As an experiment we tried pressing this waste material. One objective was to crush the shells so as to increase the bulk density; this was aimed at reducing the number of truckloads being hauled to landfill.
Another objective, with a much better payoff potential, was to separate the yolk and egg white from the shells. The yolk and egg white "juice" is classified as non-edible since it is unfit for human consumption. However pet food companies will pay $0.045 per pound for the material.
Our press definitely ground up the eggshell. The testing was done with a KP-6 press, and the press was easily overloaded. Consequently we would recommend a Series CP press for the application because it has the screw shaft supported at both ends of the press. [In 2004 this is no longer so.]
In one test we ran 56 pounds shells and got 43 pounds of fine ground shell (press cake) along with 12 pounds of "juice" (press liquor). Unfortunately the juice was (1) very foamy and (2) full of eggshell chips. But it did represent 20% yield by weight (including chips) salvaged for sale to the pet food companies.
In another test we pressed whole cull eggs. The press liquor yield was 85% of the inbound flow.
The foam was not a real problem, but it was felt that the shell bits would have to somehow be screened out.
In the end the use of a press could not be justified by Daybreak. They have installed a drain pan system at the back of the waste truck. It allows the juice to drain into a tank while the truck is being filled. The juice is rather clear, and they screen it through a 3/8"
perf sheet followed by 3/32" perf on its way into the tank. The tank holds about 25 gallons.
We did get measurements of flow rate and bulk density improvement. Ten gallons of eggshell from the truck came down to seven gallons of press cake. Flow of this material was 2,000 pph in the KP-6 at 30 rpm. On another flow test results were even a little better.
2011 UPDATE: Be sure to see the EGG SHELL UPDATE newsletter. This market has really taken off!