Over the past months, we have been contacted by the QA departments of several juice bottlers for information regarding the pasteurization of apple and other fruit juices. We have decided to post this "primer" on pasteurization to help answer some of the questions.
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Juice Makers' Dilemma
Juice makers have classically marketed juice in two extremely different forms -- completely unpasteurized/"raw" juice and ultra-pasteurized/sterile juice. The makers of raw juice have recently come under scrutiny due to safety concerns and many feel they are going to have to change their production methods in order to maintain public trust. However, these makers do not wish to ultra-pasteurize their juice because of possible changes to the flavor.
There is another option. The method by which milk has been pasteurized for decades can be considered a "middle ground" between raw and ultra-pasteurized. The flavor of milk is affected by pasteurization much more strongly than fruit juices tend to be. Therefore, methods had to be found which made the product safe, yet still palatable to the customer. This paper attempts to describes this "middle ground" form of pasteurization and provide information on the equipment required.
Background Information on Pasteurization
Before launching into the discussion of the equipment, some background information on pasteurization may be helpful. We also would be glad to link to sites containing information specifically regarding e. coli, if anyone would care to suggest any.
Pasteurization vs "Reducing Bacteria"
The process of "pasteurization" envisioned by Louis Pasteur was aimed at the destruction of all bacteria, molds, spores, etc. Pasteur discovered that the destruction of bacteria can be performed by exposing them to a certain minimum temperature for a certain minimum time -- the higher the temperature, the shorter the time required. Most of Pasteur's early experiments involved using boiling water to maintain temperature. This process killed all bacteria. Eventually, lower temperatures for longer times were determined to have similar effects. Pasteur's experiments with milk eventually proved that heating to 145 degF for 30 minutes destroyed 99.9% of the bacteria (known as a 3-log kill), which was enough to make a product safe. Long after Pasteur, micro-biologists have been able to create a "curve" of different time/temperature combinations that will sufficiently reduce a given bacteria population. These curves are different for every organism.
Note: We use the phrase "100% kill" a few times in this document. There really is no such thing as a 100% kill of any micro-organism ... ever. Some incredibly small population will always survive. When we say 100%, we really mean 99.999% or 99.9999% (5-log or 6-log) kill. A 5-log kill of pathogens is often considered the goal of any pasteurization process.
Today, many of the products available for sale are "pasteurized" using Pasteur's information. This does not mean 100% of bacteria are gone -- bacteria still exist in these products, but in very low concentrations. These products are refrigerated to keep the growth of the remaining bacteria very low. They also have a predetermined shelf-life after which bacteria concentrations rise to unacceptable levels. This is the practice for milk in the U.S. The term "pasteurized" can therefore be used to refer to products with reduced bacteria. Products with no bacteria are referred to as "sterile" or "ultra-pasteurized".
The general term "pasteurization" used in the dairy and beverage business is sometimes mis-understood. Knowing that some bacteria still exist, many people think of it as the process of destroying all the bacteria "that can make you sick". This is not necessarily the only goal. Pathogenic bacteria (those that make you sick) such as e. coli, lysteria, salmonella, and others are much more easily killed off than people may think. Making milk "safe" to drink requires much lower pasteurization temperatures than are used in the industry. There are other bacteria in milk that are not necessarily very harmful to humans, but produce the acids that sour the milk and make it undrinkable. These bacteria are called lactophilic because they consume the lactose in milk and produce lactic acid. The time/temperature required to for a 3-log kill of these lactophilic bacteria conveniently results in a 100% kill of most of the pathogenic bacteria. Therefore, the process required to simply make a product safe may not be identical to those finally decided on for the product.
Some products are actually "sterilized" before they are sold to the public. Most of the fruit juice sold on store shelves is produced this way. These products have relatively unlimited shelf life without refrigeration. However, the time/temperature combination required to kill 100% of bacteria also destroys some of the flavor components in the juice. There is some dispute over how much flavor degredation actually occurs and since this is solely a subjective opinion on the part of the consumer, no definitive data is available.
The current trend toward "natural" products has led some manufacturers to produce un-pasteurized products. These makers are relying on low bacterial counts in the raw juice and then refrigerating the product to retard growth. Makers of "natural" juice products are currently stuck in the quandary described above -- pasteurize and possibly give up some of the flavors that make their products unique or risk leaving unwanted bacteria in their product.
Accepted Methods of Pasteurization
The following methods of pasteurization are in common use across the country and are accepted by the US public health agencies.
Batch or Vat Pasteurization
The first form of pasteurization to come into use for milk was simple vat pasteurization -- heat your product to about 145 degF for about 30 minutes and you could consider the product to be safe. This method destroys most common pathogenic bacteria. However, as production demands grow, simply adding more and more vats is usually not feasible.
HTST (Short-Time) Pasteurization
High-Temperature, Short-Time pasteurization gets its name from the relatively short "Hold Time" of 15 seconds. The "High Temperature" is typically 161 degF for whole milk. It is the industry standard in the milk industry due to its simple adaptation to continuous processing. A "Hold Time" of 15 seconds can easily be achieved in a continuous process by installing a "Hold Tube". A Hold Tube is simply a length of tubing included in the system after the point where the product is heated. The tubing length/diameter is sized so that it takes a minimum of 15-20 seconds for the product to travel completely through it. If the product temperature is still at or above the pasteurization temp at the end of the Hold Tube, then the product is considered to be pasteurized. The product is then typically cooled down again for storage. Most of the milk produced in the US is pasteurized via this method. This method provides the convenience of continuous processing, yet still does not adversely affect the taste of the product by "cooking" it.
In UHT pasteurization, product is brought to over the boiling point (under pressure) for only a fraction of a second. This results in a sterile product that requires no refrigeration later. Typical applications that US residents will be familiar with are coffee creamer and juice boxes. Much of the milk in Europe is UHT pasteurized. However, after being brought to this temperature, a slight "cooked" taste is sometimes said to be detectable.
HTST (High Temperature - Short Time)
UHT (Ultra High Temperature)
Short-Time or HTST Pasteurization of Juice
Most apple juice producers are relatively familiar with both Vat and UHT pasteurization. The Vat method is used by smaller producers and UHT systems are commonly employed by the large corporate producers. We have found that very few producers in the fruit juice industry are acquainted with the process and equipment involved in HTST systems.
HTST or Short-Time Pasteurization may be an acceptable "middle-ground" for the pasteurization of juice. It will provide a safe product for the public, yet keep to a minimum the amount of flavor-degradation found in ultra-pasteurized product. Such a product will be free of pathogens with an extended shelf life under refrigeration. The following sequence of events details the general process steps. Refer to the attached flow diagram for assistance in following the flow.
Sequence of Events
In order to ensure that the process of pasteurization occurs as expected, the government requires that certain public health controls be installed on all dairy product pasteurizers. Whether or not these controls will be required on juice system is still unknown.
The question on everyone's mind is "How much is this going to cost?" The cost of a Short-Time pasteurizer can vary considerably with the required capacity. However, some costs are extremely variable while others are relatively fixed. The table below classifies the required equipment:
|Fixed Costs||Highly Variable Costs||Somewhat Variable Costs|
|Controllers/Instruments||Heat Exchanger||Flow Diversion Equipment|
|Public Health Controls||Hold Tube||Balance Tank|
|Mounting Skid (if used)|
Fully-Legal Systems vs "Heat Treat" Systems
A major question at the current time is whether or not the government is going to require full "dairy-type" controls on pasteurizers for apple and fruit juices. If fully legal controls are not required, the same functionality can be obtained via less expensive controls. In some cases, equipment can be used that is fully "sanitary", but not currently "approved" for use with milk. Since such a system has no formal definition, we are currently dubbing it a "Heat-Treat" system. The difference in price between a "dairy" type pasteurizer and a fully-functional, but non-approved heat-treat system could be quite substantial. At this time, we cannot predict if the regulatory agencies will permit the use of the word "pasteurized" on products pasteurized on non-approved system. We are aware of apple cider producers who are using this designation on non-approved systems without any trouble from the inspection agencies. There appears to be no labeling law which directly dictates the use of the word "pasteurized", but it is recommended that anyone considering the use of a system such as this should check with their local authorities before making any decisions.
The additional cost of "fully legal" controls become less significant as the size of the system increases. However, for smaller systems, the cost of the legal controls can increase the cost of the system substantially. Some producers are already being pressured by their larger customers (especially large supermarket chains) to provide pasteurized product. If the likelihood of government regulations decreases, smaller producers may wish to reduce capital investment via the use of "heat treat" systems to satisfy their customer's immediate demands. They may risk, however, being forced to upgrade these systems at a later date. The answers to these questions will only be answered when the regulatory agencies finally decide whether or not to enforce dairy-style controls on juice bottling operations.
We hope this information is useful to any producer who is
considering adding pasteurization to its beverage bottling process. We've
directed this discussion toward the apple juice industry due to the all
the inquiries sparked by the unfortunate e. coli contamination of some bottled
product. The information above can, of course, be considered valid for nearly
any other beverage product. We certainly hope that no other product comes
under scrutiny for the same reasons as apple juice / cider. We will be happy
to answer any questions. Please direct e-mail to
February 26, 1997