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INTRODUCTION
Refrigerators are a most important class of equipment. They are the
heart of the food service kitchen. They must perform longer and harder
than any other piece of equipment. Truly, the refrigerator is a silent
twenty-four hour work horse. Unfortunately, they are often taken for
granted and are the most misunderstood piece of equipment in the
kitchen. Failure to maintain and optimize refrigerators will only result
in economic losses associated with: waste and spoilage of food products,
higher than needed energy bills, dissatisfied customers, and a potential
food borne illness claim.
Understanding the fundamentals of refrigeration and cold preservation
will allow food service managers to discover overlooked problems,
optimize the use of their refrigerators, cut costs, and provide a safer
operation.
A HISTORY OF REFRIGERATION
It might be argued that one of the greatest inventions of the 20th
century is that of the refrigerator. The arrival of the industrial
revolution created a change in the geographic distribution of our
population. The majority of the population had lived in a rural farm
communities where people grew and exchanged their freshly harvested food
products with their local neighbors. A majority of these food products
were often consumed in that same day. As a larger portion of the
population migrated from their farms to the city for work in factories,
the need to preserve and distribute food products increased. Farms
became fewer, yet much larger in size. The need to provide for the safe
storage and distribution to the main markets located in the cities was
the driving force behind the development of the modern day refrigerator.
In 1924, the first self-contained mechanical refrigerator was
manufactured. This migration had also given rise to new industries. We
know them today as the wholesale/retail suppliers of food products and
the food service industry.
WHY DO WE REFRIGERATE ?
The refrigerator’s main goal is to remove heat energy and maintain safe
storage temperatures to extend the shelf life of raw and processed foods
and beverages. shelf life is a catch-all term encompassing the chemical,
biochemical, microbiological, sensorial, and nutritional stability of
foods and beverages.
TO MAINTAIN QUALITY AND MINIMIZE COSTS
Annual losses due to waste and spoilage of food products are in the
billions of dollars. The result is the needless loss of unrealized
profits from waste and unsatisfied non-repeat customers. Assuming that
fresh, properly handled food products have been purchased from
suppliers, food service managers must take the necessary steps to
preserve maximum quality once the food products arrive on their
premises. Safe, profitable food storage and preparation begin with
proper refrigeration. This starting point allows the safe storage and
the ability to preserve the quality, appearance, firmness, flavor, color,
texture, and nutritive value of food products and beverages pending
preparation and consumption. In addition, it allows stocking up to meet
peak demands and the ability to store food products during periods of
low demand.
FOR HEALTH
Preservation of food products is not only of economic importance, it is
an issue of public health. The FDA estimates that annually some 40-80
million people become ill and 11 thousand die in the United States as a
result of something they ate. Medical expenses to treat these cases are
estimated at 80 billion. The cost to a food service company is between
$1,500 and $ 78,000 to defend and settle a food borne illness claim.
Food products are all subject to deterioration by microorganisms.
Microorganisms are so minute that they cannot be seen with the naked
eye. Un-educated food service personnel generally do not consider their
existence. Pathogens are disease causing microorganisms. Within hours,
under optimum conditions of elevated temperatures and high moisture
levels, these organisms exponentially replicate themselves into the
millions on the surface of and within food products. A single cell can
replicate itself into the millions in 10-12 hours. The average
temperature range for the growth of most microorganisms of public health
significance is between 45° to 130° F. It is generally acknowledged in
the food service industry that food should not be held in this danger
zone for more than four hours. Illness can result through infection,
which is consumption of the microorganism, or intoxication, which is the
consumption of the poisonous metabolic waste (exotoxins) produced and
excreted by microorganism into its environment, the food product.
WHY FOOD PRODUCTS DETERIORATE
The major cause of deterioration and waste of stored foods and beverages
is due to inherent chemical and enzymatic reactions within food
structures and the biological actions produced by external microbial
contaminants. Temperature governs the rate of all these reactions.
Enzyme initiated spoilage is a result of carbohydrates, fats, and
proteins hydrolyzing into substances that cause break-down of protective
cells or texture alterations: flavor, odor, and color changes; the
transformation of starches into sugars, resulting in toughness;
oxidization of ascorbic acid; and so on. It can occur where the food
tissues have been wounded, desiccated or when the food reaches maturity,
at which point enzymes initiate these deteriorative activities. Simply
speaking, chemical and enzymatic reaction break-down protective tissues
which lead to infection and further degradation by microorganisms.
Microorganisms including bacteria, yeasts, and molds, also rely on
enzymes within their systems to maintain life-support activities. When
ideal conditions prevail they grow and multiply to sufficient levels to
cause disease or spoilage. Ideal conditions occur when nourishment in
the form of proteins, carbohydrates, fats, vitamins, and minerals
provided by the host food coupled with a warm, moist and a neutral to
slightly acid environment occur. The metabolic activities of microbial
contaminants result in the liberation of chemical substances that can
cause changes in foods similar to initiated by food enzymes.
Microoganisms can also release poisonous exotoxins which are toxic to
humans.
Yeasts and molds are cold loving vegetative microorganisms. Yeasts
thrive in foods with high sugar content. Yeast cultures are found in
canned foods, fruits, juices, and syrups after several days of
refrigerated storage. They are easily detected by a bubbly or froth
appearance. Taste and smell will identify yeast contamination, as an
alcohol taste and odor will appear. Most yeast metabolize foods sugars,
liberating bubbles of carbon dioxide and alcohol.Molds thrive in similar
conditions and are responsible for product storage deterioration in
juices, breads, pastries, and bruised fresh fruits and vegetables.
Microorganisms are carried into the refrigerator on produce, produce
boxes and distributed throughout the refrigerator by air circulation,
condensation and dripping. In addition, spills that are not or properly
cleaned up provide a continuous source of recontamination to incoming
fresh, cooked, and leftover foods.
Fruits and vegetables are living dynamic organisms even after detachment
from the mother plant. They continue the metabolic processes of
respiration (the-take up of oxygen, it’s distribution, utilization, and
the oxidation of energy rich cellular organic substances such as starch,
sugars, and organic acids to produce CO2, H2O, and heat energy. They
also continue to transpire (the process of water loss). Overly high
temperatures during handling, transport, and refrigerated storage
accelerate the rate of these metabolic processes and hasten ripening and
aging. The result is an increase in the production of ethylene (an aging
hormone), and the depletion of nutrient reserves (carbohydrates and
sugars) which fuel respiration and support plant cell wall tissues.
These tissues serve as a protective barrier against infection. Produce
is usually covered with microorganisms. The break-down of protective
cell wall tissues occurring from either: mechanical damage, moisture
loss from transpiration, internal tissue break-down from depletion of
supportive nutrients and/or the production of internal ethylene,
independently or in combination, open the door in the form of a wound
for these degrading microorganisms. The warmer and more humid the
conditions, the greater the rate of their infection and exponential
growth. It is impossible to eradicate these microorganisms for they are
constantly being re-introduced into refrigerators. Therefore, it is
necessary to maintain an environment that is less favorable to the
support of their growth and more conducive to maintaining the healthy
integrity of protective cell wall tissues. It is best accomplished by
maintaining low refrigeration temperatures and proper humidity control.
Meats: The shelf life of meats is generally judged as quality attributes
by consumers. They include qualities such as color, odor, flavor,
tenderness, juiciness, nutritional quality, and safety. Changes that
occur during storage include oxidation, spoilage by microorganisms,
dehydration, and changes caused by natural enzymes. Bacterial spoilage
is the major factor affecting shelf life. Most of the microorganisms
that cause spoilage of meats are either present at the time of slaughter
or are introduced during dressing, cooling and cutting in the processing
rooms. Again, low refrigeration temperatures and proper humidity control
are the best ways to control these organisms and preserve meat products.
REFRIGERATION FACTORS
Microorganisms are ubiquitous. They are constantly being reintroduced
into your refrigerators by new food products, containers and personnel.
It is virtually impossible and economically not feasible to maintain a
microorganism free refrigerated storage environment. To maintain safe
and economic food preservation it is imperative to control all of the
environmental factors that enable these microorganisms the ability to
infect, accelerate growth, and transfer to other food products.
TEMPERATURE
The most critical environmental factor in preserving the quality and
extending the storage life of food products is the control of
temperature. Temperature has an adverse affect on all perishable food
products. The rate at which molecules move (increasing with heat)
determines the rate at which they react with others or initiate chemical
reactions. Therefore, the ambient (surrounding) temperatures are
transferred into the food products increasing: the rate of respiration
and ethylene production in living plant tissues (fruits and vegetables),
as well as enzyme activity, transpiration, microbial respiration, and
growth within all types of food products. Slowing these activities are
best achieved by maintaining the lowest possible storage temperature
without freezing the food product. One-two degrees above the freezing
point of the specific food product is recommended. In smaller food
service facilities, it is difficult to maintain optimum temperatures for
different food groups, due to the limitations on the number of
refrigerators available to isolate the food groups. |
