Food Protection Trends - July/August 2020 - 260

2.5% will help processors produce a consistent product and
increase their ability to determine the necessary fermentation duration for every batch. The level of added NaCl also
impacts the flavor of the final product.
Development of an SOP for vegetable preparation and
NaCl addition promotes consistency, quality and safety in
the finished product. Since acid penetration is slower in
larger vegetable pieces than in smaller ones, a separate SOP
should address vegetable preparation so that there is consistency from batch to batch. NaCl may be added through
a dry brining method (e.g., for cabbage) or by submerging
vegetables in a liquid brine (for cucumbers, hot peppers).
Dry brining involves the direct addition of NaCl to shredded or chopped vegetables, with the subsequent release of
exudate containing plant sugars from the vegetables, creating a brine. Alternatively, NaCl can be dissolved in water
and used to cover vegetable pieces. Since the preparation
method and form of the vegetable tissue has been shown
to affect fermentation, this should also be addressed in the
SOP (28).
SOPs for vegetable preparation and preparation and
addition of NaCl therefore address: preparation of vegetable tissue, including form, e.g., whole, shredded, chopped,
etc.; the mass of each type of prepared vegetable tissue in
the fermentation vessel; the weight of NaCl added per total
mass; the method of NaCl addition, and, in aqueous applications, the amount of added water. Appropriate records
should be kept. Iodized salt, some specialty and flavored
salts, and other forms of NaCl have traditionally not been
recommended in vegetable ferments because they contain
heavy metals that may inhibit fermentation and decrease
overall quality.
CP2: Temperature and time
The temperature at which traditional vegetable fermentations proceed will impact the growth rate and rate of acid
biosynthesis. However, strictly limiting those conditions to
ensure acidification in a prescribed amount of time is not
necessary to ensure food safety. This is particularly true at
cooler temperatures, which extend fermentation periods
but do not necessarily enhance food safety risk. Typical
vegetable fermentations are held at 18-23°C (65-72°F)
for three to six weeks (52). Decreasing the temperature to
below this range slows LAB metabolic activity and extends
fermentation time but does not necessarily impact quality.
Quality impacts are, however, noted if temperature increases significantly above the desired range (>27°C/80°F)
as the result of selective growth of spoilage bacteria and
enhanced enzymatic activity that contributes to vegetable
softening, off-flavor development, and discoloration (16). It
is worth noting that excessively sluggish fermentations can
lead to quality problems and, in some cases, may increase
risk because of the development of secondary fermentations
and subsequent outgrowth of clostridial species. Effective

260

Food Protection Trends July/August

pH monitoring, as noted previously, will help detect problems that may lead to spoilage.
Park and colleagues investigated the effect of fermentation at 4 or 25°C (39 or 77°F) on the final pH of kimchi
(43). The purpose of the study was to understand the rate
at which kimchi ferments at different temperatures. Results
showed that at a fermentation temperature of 25°C it took
46 h before a pH below 4.6 was recorded, i.e., 4.21, whereas
no significant change in pH was noted for samples held at
4°C for the same period of time. The pH of cabbage fermentation brine was monitored for up to 15 days as Niksic et al.
investigated the survival of Listeria monocytogenes and E. coli
O157:H7 in sauerkraut fermented at 18 and 22°C (64.4 and
71.6°F) with NaCl concentrations of 1.8, 2.25 or 3% (39).
Regardless of fermentation condition, brine pH decreased
steadily over the first 4 days, from ~6.2 to 4.2, eventually
reaching a pH of 3.5 when shredded cabbage was fermented
at 22°C, or a pH of < 4.0 for fermentation at 18°C. A 5-log
pathogen reduction was seen over the first 4 days, with
continued log reductions until day 10, when the detection
limit was reached.
An SOP should be developed for the fermentation
process that identifies expected temperature and time for
completion of the process and options for storage post-fermentation. The SOP also identifies factors such as sealing
of the fermentation vessel. Record keeping will support
effective decision-making in the event of a fermentation
that is progressing more slowly than expected, or when
spoilage becomes an issue. Once fermentation is complete,
the processor may choose to hold the sealed fermentation
vessel at ambient or refrigeration temperatures without
compromising safety. Extended room-temperature storage
may lead to softening of texture (depending on the type and
concentration of salts present) but does not present a food
safety risk because of the low pH, high levels of organic acids present, and lack of fermentable sugars. It is best to limit
ambient temperature storage in favor of refrigerated storage
for finished products.
CP3: Packaging for shelf stability
Vegetable ferments may be packaged as a shelf-stable product or packaged and stored under refrigeration.
Effectively performed, the fermentation process achieves
a 5-log pathogen reduction and uses up simple sugars, so
that thermal processing is not required for product safety.
Pasteurization will, however, inactivate the fermentative
cultures that may continue to produce carbon dioxide and
acid during storage, thus helping to stabilize the product.
Processors packaging fermented product in hermetically
sealed containers without a thermal process would need to
verify shelf stability (1).
Packaging involves placing fermented vegetable tissue,
either hot or at room temperature, into containers with added fermentation brine or acidic cover-brine and applying

Food Protection Trends - July/August 2020

Table of Contents for the Digital Edition of Food Protection Trends - July/August 2020