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Why Pasteurize Juice and Cider?

Historically there had been little concern about the safety of apple cider. The high acidity, typically around pH of 4, acts as a natural barrier against most microorganisms. However, due to multiple outbreaks of E coli O157:H7, along with Salmonella and Cryptosporidia in the last 15 years, there has been an increased concern about the safety of all fruit and vegetable juice products. There has been an estimated 16,000 to 48,000 juice-related illnesses each year (NFPA 1999). The outbreaks have exhibited the ability of E. coli O157:H7 to be sustained at low pH and refrigerated temperatures.

This spawned somewhat of a scramble to develop better pasteurization methods and equipment in order to save the juice and cider industry. In the beginning there was simply thermal/heat pasteurization, but within the last decade there has been a vast number of pasteurization methods developed. Every new method is an attempt to find a better way of pasteurizing. Better, in terms of pasteurization, usually means to further extend shelf life and preserve taste, look, and other sensory aspects, while effectively killing harmful bacteria and pathogens. This article is an attempt to give a brief overview of the current pasteurization methods and technology.

Current Pasteurization Methods as of February 2013:

    Thermal:

  1. Low Temperature Long Time Pasteurization (LTLT)
  2. High Temperature Short Time Pasteurization (HTST)

    Non-Thermal:

  1. High Pressure Processing(HPP)
  2. Ultraviolet Light (UV)
  3. Pulsed Electric Field (PEF)
  4. Power Ultrasound (US)
  5. Hydrodynamic Cavitation(HC)
  6. High Pressure Homogenization (HPH)
  7. Membrane Filtration (Ultrafiltration and Microfiltration)
  8. Chemical Methods / Preservatives

Low Temperature Long Time Pasteurization (LTLT)

LTLT has been traditionally pasteurized by batch heating at 145 F for ½ hour to 1 hour. One could see these units at small dairies in the old days. Milk for cheese production is still done this way in small cheese plants. This method has been replaced by high temperature short time treatment due to the undesirable quality changes during the process.

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High Temperature Short Time Pasteurization (HTST)

HTST could minimize those undesirable quality changes inherent in the LTLT method due to the much shorter processing time. Currently, HTST is the most common method for heat treatment of fruit juice, and the method underlying most pasteurizers made my Goodnature Products. In these units apple juice, for instance, is quickly heated from cold to hot (160F), held for just 15 seconds, and then rapidly cooled until cold again. The entire process can take place in less than a minute.

    Advantages of HTST:

  • Most well documented and widely used method.
  • Many standards have been established.
  • Works on cloudy, clear, puree, etc.
  • Can be done on a large scale continuous flow prior to filling, or in the bottle after filling (tunnel pasteurization).
  • Can kill spores at a high enough termperature.

    Disadvantages of HTST:

  • Many people notice a slight taste, color, and odor change after heat treatment. It is often perceived as “processed” tasting, and less “nutritious” as it does interrupt many natural reactions, and kill enzymes.
  • Orange juice does not settle out because the PME (poly methyl esterase) enzyme is no longer active.

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High Pressure Processing (HPP)

HPP was actually developed more than 20 years ago, originally as a method of treating seafood and meat, which cannot be thermally pasteurized. Through the use of extremely high pressures (60,000 psi) for usually about 5 minutes, the microbes are “crushed” to death.

    Advantages of HPP:

  • Very effective on E coli of all types as well as other microbes like Listeria and Salmonella.
  • Can be performed on bottled juice so long as the bottles are flexible enough.
  • Have been recognized by the FDA as providing a 5-log kill.
  • Many juice producers are already using it.
  • Does not affect flavor or nutrition of the juice as much as thermal techniques.

    Disadvantages of HPP:

  • Expensive. Currently $1Million - $3Million per unit.
  • Very heavy and energy intenstive with huge hydraulic power supplies.
  • Installation requires special foundations to support the weight of 3 inch thick steel walls.
  • Adds about $0.35 USD per liter to the cost of the juice.
  • Glass containers can not be used.
  • Works only on juices that are already in the bottle and capped.
  • Does not kill spores.

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Ultraviolet Light (UV)

UV Processing was originally developed in conjuction with Cornell University as a cheaper method than thermal for seasonal apple cider producers, many of whom could simply not afford a thermal pasteruizer.

    Advantages of UV:

  • Small models are very inexpensive, approx. $15K to $30K USD.
  • Easy to use.

    Disadvantages of UV:

  • Not absolute, as cloudy juice can contain particles that block the light. Works best on water and non-cloudy liquids.

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Pulsed Electric Field (PEF)

PEF uses lower than thermal pasteurization temperatures, and a pulsed high voltage (25,000 Volts) across a gap through which the juice flows. This allows for lower temperatures than thermal pasteurization. As many as 2,000 pulses per second are administered. Much of the earlier development work was done at Ohio State University in the late 1980's and 1990's.

    Advantages of PEF:

  • Less expensive than HPP, although the machinery has a cost still approaching $1Million.
  • Cheaper to run than HPP, only adding about $0.03 to $0.07 USD to the cost of a liter of juice.
  • Performed on bulk juice that is flowing through pipes, so it can handle relatively large production volumes.
  • Retains the original sensory and nutritional characteristics of the juice.
  • Environmentally friendly as it produces no waste.

    Disadvantages of PEF:

  • Requires an expensive aseptic filler because it only works before the juice is bottled.
  • Does not work on spores.
  • Still not widely available or accepted but is becoming more so.

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Power Ultrasound (US)

Power Ultrasound has proven to kill microbes by the application of high energy sound waves (usually 20,000 cycles per second, which is just above the normal hearing capacity of the human). The principle of ultrasound is the formation of small bubbles that, when they collapse, produce very high pressure and temperatures which can destroy microbes in the immediate vacinity of the bubble.

    Advantages of Power Ultrasound:

  • No heat applied
  • Minimal damage to liquid

    Disadvantages of Power Ultrasound:

  • Ultrasound transducer not available in large enough scale for a commercial juice producer.
  • Cannot achieve a 5-log kill without supplemental heat.
  • Not commerically aviable at this time.

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Hydrodynamic Cavitation

Hydrodynamic cavitation (HC) processing is an interesting technique wherein the juice is forced through orifices under high pressure, causing the same type of small vapor bubbles as in power ultrasound, but in this case the energy is coming from a pump rather than a sound generator.

    Advantages of HC Processing:

  • Higher production volumes are possible as compared to ultrasound.

    Disadvantages of HC Processing:

  • Still under development, and not completely understood.

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High Pressure Homogenization Processing (HPH)

HPH pasteurization is a promising non-thermal technology for fruit juices. It uses high pressure pumps and high turbulence, common in traditional homogenizers, to shear, break, and otherwise disrupt the cell walls. It is still under development at this time

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Membrane Filtration Processing

Membrane filtration, both ultrafiltration (UF) and microfiltration (MF) are the commonly used membrane filtration techniques for fruit juice processing. Traditionally these methods are used for filtration, and are able to actually filter out microbes as well. The effectiveness depends on many factors and is generally more applicable for more processed juices that are filtered anyway, like clear apple juice, hard cider, or beer. Since these methods cause color changes and some flavor changes, they are not widely used for natural juices that contain a cloud.

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Chemical Methods/Preservatives

Although not considered a pasteurization method, some chemical preservatives are widely used for the shelf-life extension of fruit juices and beverages. Potassium sorbate and sodium benzoate are the standard preservatives. The market is trending away from preservatives in favor of pasteurization.

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Conclusion

In summary, there are many new and interesting pasteurization techniques under development but as of now the only choices for a commercial juice producer are HTST, HPP, and PEF, with the majority of producers using HTST, but considerable interest in the other two.

Looking to Purchase Pasteurization Equipment?

Goodnature products manufactures and sells custom models of both HTST and PEF pasteurizers. For more information on pasteurization equipment, please send an email to sales@goodnature.com , call us at 1-800-875-3381, or request a quote.