December 22, 2017
September 2019 Update
Back to the drawing board. It has not been possible to repeat the initial results. Orange and mandarin waste was stored anaerobically and then run through a screw press. Instead of going through the press like it did in our original video, it became spoiled and slimy, and no moisture could be squeezed from it. Hydrated lime was added, but no useful chemical reaction occurred. The peel would not dewater in a screw press.
That failure has motivated us to issue this revision to our original newsletter.
This process would had have potential if we could make it work. So we have decided to try one more thing. Some fresh peel, without hydrated lime addition, will be pressed. This initial pressing should remove up to 25% by weight of oily emulsion. The remaining 75% (press cake) will have a moisture content still in the low 80%’s. It will be stored in anaerobically, but with provision for draining any free liquid which is released. An option will be tried where hydrated lime will be sprinkled on the press cake from this pressing, before the anaerobic storage. We’ll let you know how it turns out.
At least our original newsletter, below, started with the word “SOME”:
SOME ENSILED CITRUS PEEL WILL PRESS THE VERY SAME AS PEEL WHICH HAS BEEN REACTED WITH HYDRATED LIME
That was the interesting conclusion from trials run earlier this year in Tampa and Spain.
This question arose because small citrus processors, plants with only a few orange juice extractors, do not generate enough citrus waste to justify a citrus feedmill. The citrus feedmill would need to be sized for production peak flow, even though the equipment would be underused or even idle most of the time.
The idea posed was: What if that the peel could be stored, allowing it to ensile, before it was pressed? With that process the ensiled peel could be fed to the feedmill at a steady year-round rate. This would greatly reduce the factory investment by avoiding the need to size everything for the peak harvest months.
It was known that ensiling occurs if orange peel is pressed and then stored in an anaerobic condition. Pressing News #289 CITRUS WASTE DISPOSAL describes the process. This new effort involved pressing peel after it ensiled instead of before.
As luck would have it, Cook Manufacturing had access to ensiled citrus peel. This was peel from Brown extractors, as can be seen in the video. It turned out to be grapefruit peel, and it is significant that this peel is on the acidic side with, a pH of only 3.5 or lower.
We had anticipated that it might be necessary to shred this peel. However it became evident that the ensiling process made the peel fragile; it broke up while going through the screw press.
Before fresh citrus waste can be pressed, it is necessary to first react it with hydrated lime. This is done to break down the pectin so that moisture is released. We wondered if that would be necessary with the ensiled peel, so we tried it both ways. The trials showed no improvement when treated the peel with lime. We figure that the ensiling process must break down the pectin.
Here is the link to the video made during the testing in Tampa:
PRESSING ENSILED CITRUS WASTE https://youtu.be/SacG7z0OzUE
When fresh orange peel is reacted with lime and then pressed, the moisture content of the fiber is reduced from 78-82% down to 73-75%.* When pressing our ensiled grapefruit peel, without lime, the results were the same, going from 82% as-received to 75% coming out of the press. Thus we concluded the ensiled peel presses the very same as peel which has been reacted with hydrated lime.
HOWEVER: Following the success of the initial trial, a complete failure was experienced. Fresh citrus waste was placed in a sealed plastic container for over a month. Instead of ensiling, the peel formed a gelatinous mass which could not be dewatered with a screw press. It seems possible that this peel had too high a pH (such as 4.5) or too low a sugar content for ensiling to occur. This would tie to the citrus variety. Or it may be that for ensiling to occur, the waste must be piled on open ground, allowing free liquid to drain off.
Further trials are underway.
*If citrus molasses, made from the press liquor, is added back in the feedmill process, the press cake can be reduced to 62-65%. But that is a different story.
Issue #301