Lemon juice processing

An important crop in Italy and some other Mediterranean countries, the lemon is also grown commercially in the United States. The characteristic oval-shaped, yellow fruits, apart from their culinary use, are an important source of juice and flavouring for the soft drinks industry.

The main criteria for juice processing, on the other hand, are more straightforwardly that the fruit should be sound, of good quality, and of correct maturity. If the fruit producer has followed GAPs and the harvest and handling have been accomplished effectively, fruit arriving at the processing plant should be reasonably sanitary and of optimum quality, thus simplifying succeeding operations.

The following are the key manufacturing stages:
*Selection and preparation of raw material
*Juice extraction
*Filtration (optional)
*Batch preparation
*Pasteurization
*Filling and bottling

There are several methods to extract juice depending on the type of fruit used. The goal in juice manufacture is to remove as much of the desirable components from the fruit as possible without also extracting the undesirables.

Juice extraction equipment ranges from hand operated crushers to tonnes/hour mechanical extractors (Figure 6.5). With soft or comminuted fruit a cone screw expresser or paddle pulper fitted with appropriate screens serves to separate the juice from particulate matter.

In the separation of juice from its fruit, the traditional method has been to apply pressure to the mashed, or pulped, fruit in order to force the liquid portion through a cloth or some form of screen.

In the horizontal rotary press, mash is pumped into the press to partly fill the cylinder space. The piston then moves forward under hydraulic pressure to express the juice by consequently forcing it through the filter sleeves and along the channels in the drainage cores, to be fed through outlets in the specially designed plates for collection in a juice tank. The piston then withdraws whilst a second mash charge is received and the process repeats. During the pressing operation the endplate of the unit rotates with consequent meshing of the filter-lines, so that at the end of a pressing cycle the lines are loosely meshed together within the press-cake, or fruit pomace.

A thermal screw is a continuous system for both transporting and heating or cooling crushed fruit or whole small fruit. In a hot press regimen, the material passes directly from the crusher to the press holding tank via the screw, adjusted to deliver the crush at the proper temperature for enzyme activity, ~60ºC. In continuous pressing, the screw can even be slowed down enough to accomplish the holding time and then feed directly to the press (or to another feed/holding screw).

When the juice or pulp has been collected, it is necessary to prepare the batch according to the chosen recipe. This is very much a matter of choice and judgment, and must be done carefully to suit local tastes.

Clarification is an important processing step used by the lemon juice industry. Clarification is necessary in order to obtain a bright, clear product with low viscosity. Clarification of juice involves the use of bentonite gelatin and silica sol as fining agents.
Lemon juice processing