Table Olives
The olive fruit is a
drupe. It has a bitter component (oleuropein), a low sugar content
(2.6-6%) compared with other drupes (12% or more) and a high oil
content (12-30%) depending on the time of year and variety.
These
characteristics make it a fruit that cannot be consumed directly from
the tree and it has to undergo a series of processes that differ
considerably from region to region, and which also depend on variety.
Some olives are, however, an exception to this rule because as they
ripen they sweeten right on the tree, in most cases this is due to
fermentation. One case in point is the Thrubolea variety in Greece.
Oleuropein,
which is distinctive to the olive, has to be removed as it has a strong
bitter taste: it is not, however, pernicious to health. Depending on
local methods and customs, the fruit is generally treated in sodium or
potassium hydroxide, brine or successively rinsed in water.
SEMI-RIPE OLIVES
These
are obtained from olives that are picked when their colour is starting
to change. They are harvested before full maturity, when the flesh is
quite firm and oil formation has not concluded. The process of
darkening the fruit by oxidation is typical of California. Olives
suitable for processing as green olives are selected as they enter the
factory, then placed in brine at concentrations between 2.5 and 10
percent in inverse relationship to fruit size, and they are protected
from air.
The olives are placed in large concrete tanks in an
initial solution of 2 percent lye until they are ready for subsequent
preparation. When they are to be prepared for the market, they are
placed in low-concentration lye and then washed in water into which
compressed air is injected. Further treatments in dilute lye, each
followed by aeration, facilitate penetration through to the stone.
Next, the olives are washed to eliminate lye residue and to lower the
pH to close to neutral. Solutions of 0.1 percent ferrous gluconate or
lactate are often applied to enhance fruit darkening. After placement
in brine for a few days, the olives are ready for canning. Heat
processing in the form of temperature and pressure-controlled
sterilisation is fundamental to ensure the product keeps properly.
GREEN OLIVES
Green
olives are obtained from olives harvested during the ripening cycle
when they have reached normal size, but prior to colour change. They
are usually hand picked when there is a slight change in hue from
leaf-green to a slightly yellowish green and when the flesh begins to
change consistency but before it turns soft. Colour change should not
have begun. Trials have been run to machine harvest table olives, but
owing to the high percentage of bruised fruit they had to be immersed
in a diluted alkaline solution while still in the orchard. Recently
harvested, the olives are taken to the plant for processing on the same
day if possible.
How are they Processed?
Green
olives are processed in two principal ways: with fermentation (Spanish
type) and without fermentation (Picholine or American type).
Spanish or Sevillian Style
The
olives are treated in a diluted lye solution (sodium hydroxide) to
eliminate and transform the oleuropein and sugars, to form organic
acids that aid in subsequent fermentation, and to increase the
permeability of the fruit. The lye concentrations vary from 2% to 3.5%,
depending on the ripeness of the olives, the temperature, the variety
and the quality of the water. The treatment is performed in containers
of varying sizes in which the solution completely covers the fruit. The
olives remain in this solution until the lye has penetrated two thirds
of the way through the flesh. The lye is then replaced by water, which
removes any remaining residue and the process is repeated. Lengthy
washing properly eliminates soda particles but also washes away soluble
sugars which are necessary for subsequent fermentation.
Fermentation
is carried out in suitable containers in which the olives are covered
with brine. Traditionally, this was done in wooden casks. More
recently, larger containers have come into use that are inert on the
inside. The brine causes the release of the fruit cell juices, forming
a culture medium suitable for fermentation. Brine concentrations are
9-10% to begin with, but rapidly drop to 5% owing to the olive’s higher
content of interchangeable water.
At first Gram-negative
bacteria multiply, but after a week and a half they disappear. They are
a consequence of contamination produced in the plant installations, and
in the atmosphere and brine and can be avoided by stepping up hygiene
measures. At a pH level of 6 and upwards, lactobacilli develop
massively until the Gram-negatives disappear and the brine attains a pH
of 4.5. There is a predominance of Lactobacillus plantarum which
produces lactic acid from glucose almost by itself. When the
fermentable matter is spent, acid formation ceases. Yeasts appear
together with the lactobacilli. Fermentative yeasts do not cause
deterioration but oxidant yeasts consume lactic acid and raise the pH
level and may therefore jeopardise the process.
Under certain
conditions normal fermentation processes can be altered by the presence
of undesirable microorganisms which can transmit poor organoleptic
properties to the olives or impair their keeping properties. Gas pocket
fermentation is caused by the Gram-negative bacilli in the first stage
of fermentation, but can be controlled by intensifying hygiene
precautions when the olives are delivered to the plant, as well as
during lye treatment and washing. If gas pockets still appear in spite
of these measures, the pH level can be lowered to 4 by adding an acid.
Butyric fermentation is well controlled by ensuring the proper pH
level. Putrid fermentation is caused by poorly-kept containers and bad
water. Lastly, there is a type of deterioration known by its Spanish
name of “zapatería” (cobbler’s) which produces an unpleasant taste and
odour at the end of the fermentation process, often coinciding with
rising temperatures in the spring or early summer. It is produced by
bacteria belonging to the Clostridium and Propioni-bacterium genus. The
right combination of brine concentration and pH level (5% salt and 4.5
pH) helps to control fermentation processes.
When properly
fermented, olives keep for a long time. If they are in casks, the brine
level must be topped up. At the time of shipment, the olives have to be
classified for the first or second time as the case may be. The
original brine is replaced and the olives are packed in barrels and tin
or glass containers. Sometimes they are stoned (pitted) or stuffed with
anchovies, pimento, etc.
The most commonly used varieties are Manzanillo, Gordal and Moroccan Picholine.
Picholine Style
Olives
belonging to the Picholine variety from Languedoc and Lucques in
southern France are prepared in this manner, as are other varieties
from Morocco and Algeria.
The bitterness of the olives is
removed by treating them in a 3-3.5º B lye solution in which they are
left for 8 to 72 hours until the lye has penetrated three-quarters of
the way through the flesh. They are rinsed several times over the next
day or two, and then placed in a 5/6% brine solution for two days. A
second 7% brine solution is prepared, and acidity is corrected with
citric acid (pH 4.5). After 8-10 days they are ready to be eaten and
retain their intense green colour. Sometimes the consignment has to be
postponed, and it is necessary to store the olives. This is easy, as
long as temperatures do not rise. The olives can stay in an 8% brine
solution until spring, but then it has to be raised to 10%. In larger
installations they can be kept in cold storage, at a temperature of
between 5º and 7º C, in a 3% brine solution.
Before shipment, the olives are washed repeatedly, sorted and packed in suitable containers in 5º or 6ºB brine.
RIPE OLIVES
There
are olives that are harvested when the fruit is close to full ripeness,
once it has attained the colour and oil content corresponding to each
particular variety. The are many types of preparations depending on
local tastes. Those in greatest commercial use are now outlined.
Black Olives in Brine
These
are typical of the eastern Mediterranean countries; in Grecce they are
from the Conservolea variety, which grades at around 200 fruits per
kilogram, and in Turkey they are made with the Gemlik variety. The
fruit is picked by hand when black ripe, but before the olives
overripen or are shrivelled by frost. They have to be transported as
quickly as possible to the processing plant where they are sorted,
washed and immersed in 8-10 percent brine. Large-scale plants use big
10-20 tonne tanks while small-scale processors continue to use wooden
vats. At the start of fermentation the tanks are tightly sealed because
the olives must not be exposed to air. The brine stimulates the
microbial activity for fermentation and reduces the bitterness of the
oleuropein. It drops to a concentration of 6 percent, which makes it
necessary to increase it to 8 percent and even 10 percent, while
homogenising it by operating a pump to activate circulation.
\When
the bitterness has been sufficiently weakened – how long this takes can
vary greatly – the fruit can be sold. The colour fades during the
process, but is corrected by aerating the olives for two or three days,
although sometimes they are treated with 0.1 percent ferrous gluconate
or lactate to make them a deeper black. Lastly, the olives are selected
and packed in barrels or internally varnished cans, which are filled
with 8 percent fresh brine. They are popular on the market because of
their slightly bitter taste and aroma.
They are also packed in
vinegar (25 percent of brine volume) and may even be heat processed; a
few grams of oil are then added to each can to form a surface layer.
The Kalamata variety is prepared in this way; the elongated,
medium-sized olives are slit to absorb the flavour of the marinade and
then canned.
Black Olives in Dry Salt
Also
of Greek origin, these are prepared using overripe olives of the
Megaritiki variety. They are vigorously washed and placed in baskets
with alternating layers of dry salt equivalent to 15 percent of the
weight of the olives. The end product is not bitter, but salty, and it
looks like a raisin; it is for local consumption.
Finally, a
mention should also be given to the numerous styles of table olive
preparations in the different olive-growing regions. Some examples are
olives treated solely with water to sweeten them prior to crushing or
splitting, which facilitates washing. In many cases, the olives are
eaten after being seasoned with herbs, pieces of orange, lemon, garlic,
paprika, oregano, etc. Until the turn of the twentieth century, the
table olive market was local, but since then it has expanded to
non-producing areas where table olives have become popular. This is
particularly true of the Spanish, Greek and California types.
Back to
Olive Page
|