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Soda in the treatment of table olives

Directions for use. With some useful advice on the debittering process from the expert Mario De Angelis

Caustic soda is the common name of sodium hydroxide (NaOH), which can be purchased in flakes, drops or beads. The first type is the more common, especially in 1 kg packages. It can be bought in chemicals suppliers stores or in groceries. The treatment has to last for 8 to 12 hours, and to end when the soda has penetrated the flesh for about ¾ to 4/5 of its depth. The treatment with soda debittering ends when the flesh by the pit, not attacked by the soda yet, is 1-2 mm thick.

To control the part attacked by the soda, some olives have to be cut longitudinally, down to the pit. After a few seconds, the flesh interested by the penetration of the soda darkens, while the rest remains white.

The concentration of the soda solution is normally 1,8-2,1% (e.g., 2% means 20 g per liter of water) and it has to be at room temperature. When the soda is immersed in water, an exothermic reaction takes place. For this reason, the solution has to prepared by dissolving the soda in some water (stir well while pouring the soda, being careful not to breath the fumes which are exhaled), and then more water should be added to obtain the desired concentration. For example, 10 liters of 2% solution can be prepared by dissolving 200 grams of soda in 4 liters of water, and by adding 6 liters in the following, to obtain the desired 10 liters volumes.

Olives are then put in a plastic food container, including a press, or in other food containers (terracotta, glass, etc.), but not in a metal container. The container has to be full before the solution is poured until it covers the fruits.

The capacity of a container will be taken by the olives for 60-65% and by liquids for the remaining 35-40% (soda solution, water, pickle).
When preparing the solution, some liters of solution in excess should be prepared. In all phases of the process the olives need to be totally immersed in the liquid, which is the reason why the press should be in plastic, seasoned wood or white cloth, but not metal.

During the process, the level of the solution covering the olives need to be maintained by repeatedly filling up the container. The level gets lowered because the olives absorb the water during the first hours of the treatment.

At the end of the process, the soda is washed out by 3-4 washings with drinkable water, in the span of 24.30 hours, then prickle is added (sodium chloride in water, the common cooking salt) at an 8% concentration (80 grams of salt per every liter of water).

The concentration should be stabilized by repeatedly adding salt, only after determining the concentration with a densitometer or via a chemical method. The obtained result allows to carry out the necessary computation to determine the needed quantity of salt. It is not appropriate to add quantity like 3% in one solution, in order to prevent olives from wrinkling. The salt has to be added twice, with the two additions 48 hours apart.

by Mario De Angelis
01 november 2010, Technical Area > Olive & Oil