the lye treatment and washing, fermentable sugar may be added to the
brine.
Complex sequences of bacteria have been reported by different inves-
tigators but the most important species appears to be Lactobacillus
plantarum. Several other LAB have been reported, including an early
phase of growth byLeuconostoc mesenteroides. This, in particular, will
depend upon the salt level used sinceLeuc. mesenteroidesis not markedly
salt tolerant. Essentially though, the decreasing pH, increasing acidity
and the salt combine to eliminate the natural microflora dominated by
Gram-negatives and replace it with one composed of lactic acid bacteria
and some yeasts. The fermentation process lasts for several weeks and
culminates in a product with a pH of 3.6–4.2 containing around 1%
lactic acid. Starter cultures are available but rarely used at present, the
most important measure taken to control the fermentation is to ensure
that air is excluded from the fermenting product to prevent the growth of
oxidative moulds and yeasts.
The traditional Greek-style product, natural black olives in brine,
accounts for 31% of world production. Processing starts with ripe olives
which are placed in a higher strength brine than Spanish-style olives,
usually containing up to 10% w/v salt. Fermentation is very slow
because the absence of a lye treatment means that oleuropein is still
present and that nutrients diffuse slowly through the tough fruit skin.
The microflora is usually dominated by yeasts of which a large number of
different species have been isolated and identified including members of
the genera Saccharomyces, Hansenula, Candida, Torulopsis, Debar-
yomyces,Pichia,Kluyveromyces, andCryptococcus. Lactic acid bacteria
may be significant if the salt content is low (o6–7%) but are generally a
minor component. As a result, there is less acid production than in low-
salt vegetable fermentations and the final product generally has a pH of
4.5–4.8 and a total acidity of 0.1–0.6% expressed as lactic acid. This is
not sufficient to confer reasonable stability on the product so the salt
content is usually increased to above 10% for storage.
9.7.3 Cucumbers
Lactic fermentation following pickling in a brine was once the only
method for successful preservation of cucumbers. Since the 1940s, ‘fresh
pack’ techniques have evolved which do not require a fermentation to
confer stability. The first of these is based on direct acidification with
vinegar or acetic acid followed by pasteurization while more recently
direct acidification coupled with refrigerated storage has become increas-
ingly popular. Today in the United States, where more than half a
million tonnes of cucumbers are preserved each year, only about 40% are
preserved by fermentation, approximately equal volumes are pasteurized
Chapter 9 341