Last month we had an opportunity to runs tests with mushrooms.  Button mushrooms were purchased at the produce market, and we tried squeezing liquid out of them using a variety of tactics.

The most interesting thing that happened occurred when we used steam injection in a screw press.  This, as hoped, did increase the dewatering.  But what was strange was that the press liquor, as it cooled down in our sample collection bags, turned into jelly.

We started running the fresh mushrooms in a laboratory CP-4 press.  A video of this is posted on YouTube; enter VincentCorp1931 on their web site and you should be able to find it.  Extremely low air pressure had to be used on the discharge cone, and low screw rpm.  Even then the material channeled (squirted) out from one side of the cone.  50% juice yield was obtained.

Because of the channeling, our next test was run with a KP-6 press with the rotating cone option in play.  This eliminated the channeling, and much better results were obtained.  The mushrooms as we received them had 93% moisture content; this went down to 91%, with a 25% juice yield.

In order to improve the moisture reduction, we switched screws in that press.  Re-running the test with a screw with a tapered shaft made a notable improvement.  50% juice yield was obtained, and the moisture content of the press cake dropped to 90%.  The tapered shaft adds a third squeezing mechanism to the normal tightened pitch of the screw flights and pressure exerted by the discharge cone.

Since it was still possible to squeeze quite a bit of liquid from the press cake, we tried double pressing.  It appeared that the mushrooms were torn apart in the first pressing.  Consequently, with the second pressing, a significant amount of additional juice was obtained.  The moisture content of the press cake dropped a couple percentage points, to 88%.

Along the line we chopped some mushrooms, and we put them in a Baggie with some hydrated lime.  With a bit of massaging, it was evident that a chemical reaction was occurring that released moisture.  So, we took some of our press cake from previous runs, added 3% hydrated lime, and tried pressing that.  The results were impressive.  An extremely dry press cake was produced, with only 74% moisture content.

While the press liquor generally seemed rather clear, the dry matter solids in it measured fairly high.  Checking the Brix, we found that mushroom juice measures 3° to 4° Bx.  That helps explain the high dry matter content of the press liquor.  In all of our trials the total dry matter content of the press liquor measured 5% to 6%.

Our final test of the day involved pressing fresh mushrooms in a screw press that was set up for steam injection.  Steam was injected through the resistor teeth, achieving temperatures around 160 F.  As with fresh organic materials like orange peel and fish, a great deal of moisture was released from the mushrooms.  This took the mushrooms, with 93% as-received moisture content, down to 89% moisture in the press cake.

This was the test with steam injection which lead to the observation that the press liquor, which flowed freely from the screw press, turned in jelly once it cooled down.

There is one thing we did not try which would work very well.  If a shredder were mounted over the inlet to the screw press, surely high juice yield would be obtained.

Test results are pasted below:

SUMMARY OF TEST RESULTS: