Ultra Heat Treatment Milk Processing

UHT Milk Processing Record Format
UHT Milk Filler HACCP Sample
UHT Milk Filler Process Flow sample

Introduction to UHT processing options

There are a number of processing options for UHT milk depending on your requirements for automation, quality and cost of processing and capital cost of equipment. UHT is a process where the milk, juice, beer, wine, beverage etc is heated to approx 145 degrees C and held there for some two seconds. The UHT heat treatment time and temperature combination should be established based upon the product to be treated and it's viscosity, taste,colour, smell etc. UHT milk after heat treatment is pumped to a Sterile tank (Steri tank) to give a buffer prior to filling. Filling is usually done in a sterile atmosphere (Aseptic) where the UHT packing machine flushes the package with Nitrogen and also keeps the area within the filling heads flooded with Nitrogen to eliminate any air contamination as bacterea, moulds etc require air to grow. The shelf life of a UHT product can be up to 1 year at ambient temperatures.

UHT heat treatment can affect the flavour of the product and time and temperature combinations should be established to minimize this effect

The equipment required for uht is straightforward and the first part is a UHT processing line (Heat treatment to a high temperature and also holding section)


Generally UHT plants are tube in tube, plate heat exchanger, shell and tube, scraped surface or direct steam injection and all systems will have a simple holding section matched to the product and required holding time.
The type of systems vary in the degree of automation and also damage to the product so careful selection of the type of system should be made based upon accepted industry standards for the product to be heat treated
The immediate advantages of the aseptic process settled its success wherever it has been introduced. This technique allows products, formerly considered perishable, to be stored and distributed without refrigeration for prolonged periods of time (from 6 to 24 months depending on the product). In addition, the aseptic package ensures a contamination free product with virtually no loss of quality, taste or nutritional values. The aseptic process can be utilized to package a wide range of products, such as milk and dairy, fruit juices, flat drinks, wine, mineral water tomato sauce and others.

ASEPTIC PACKING LNES

The aseptic packaging machine forms, fills and seals packages in one continuous operation in a sterile environment.

The first "step" of the aseptic process is the sterilization of the product by heating and then cooling. The treatment temperature and holding time is varied according to the type and viscosity of product. The package seal is based on an internal polymer and internal polymer melting and eliminating exposed edges from the inside of the package.

For sterilization, hydrogen peroxide (H²O²) may be utilized depending on country legislation and the sterilizing agent at the end of the sterilization residues is less than 0,5 parts per million

1. UHT MILK

Direct Steam injection.

Direct steam injection is the most economical process operationally as it uses less steam (injected direct into the product giving 100% heat exchange)

Equipment manufacturers do not generally classify this as the most efficient process as there is no heat exchanger to recover the heat for preheating, this could be specified and would increase the capital cost as it would require a specialist design which included direct steam injection and a heat exchanger to heat the incoming cold milk with the outgoing hot milk which would result in a lower steam consumption and less waste heat.

The heat exchanger (tube in tube or plate) is replaced with a steam injection unit which is likely to be a lower cost and easier to clean and maintain and also have longer running hours. (tubes and plates have a build-up of bio-films and scale)

The time and temperature combinations for direct steam UHT milk Processing are likely to remain similar other UHT process heating methods.

Culinary Steam:

One of the main requirements of Direct Steam UHT is to have true culinary steam as normal steam may have traces of boiler chemicals and carries a higer risk of contamination in the event that the boiler is overdosed or has chemical carry over. Culinary steam has for years caused concern for manufacturers with engineering suppliers designing filtration units to filter out any rust of other particles carried over from the steam boiler and its pipework. Boiler chemicals need to be on an approved list for addition to boiler feed water and pipework should be of stainless steel. The addition of boiler chemicals is difficult to guarantee the process and the individual chemical and carryover. As the testing of finished products becomes more economical and frequent then this poses in my view an unacceptable risk to big brand dairy manufacturers. The only true culinary (edible) steam would be produced from water not requiring chemical treatment e.g reverse osmosis or ultrafiltration used to remove the excess salts from the boiler water befor turning into steam. This combined with all stainless steel pipework and fittings would give a true culinary steam.This is particularly important where infant milk is produced which should not contain any traces of contaminants (subject to in country laws)

Compressed Air - Sterile Air

Where compressed air is used to maintain a sterile environment in pipes and tanks then this should be clean and oil free which is usually established using carbon and other filters and having stainless steel lines which are cleanable. Where the atmospher in the filling line needs to be clean sterile air (heppa filtered) or an inert gas such as Nitroge is used. An inert gas is better than air as air will cause oxidation (oxidative rancidity) in products containing fat. Nitrogen is usually generated on site using Nitrogen filters. If Co2 is used then this is usually bought in in liquid form and required specialist designed tanks and lines and special attention paid to safety. Co2 is generally used in combination with nitrogen as when used alon it is absorbed into the product and can create a negative poressure in the container. This is particularly important for exporters going to higher or lowere elevations where the artmospheric pressure change can result in blown or compressed packages due to the fixed pressure in the can / package.

2. UHT

Indirect plate heat exchanger.

Indirect steam via a plate heat exchanger is the oldest / most well established method of Ultra heat Treatment (UHT) of milk but it does carry with it some disadvantages compared to a tube in tube or tube in tube heat exchanger.

Due to the need for efficient heat transfer, a thin corrugated steel plate is used. The corrugations are to give the sheet strength and to create turbulence. There are also raised nipple areas where there is plate to plate contact to maintain a gap between the plates. The plates are designed in such a manner that steam / cooling water flows on one site of the plate (heating medium) and the milk / water / cleaning solutions on the other side of the plate. The big plus with this type of plant is the small footprint and very efficient hear transfer. The downsides are numerous,

  • 1. If a pinhole occurs in a plate then is can be difficult to trace and may cause increasing contamination.
  • 2. Fluctuations in pressurfe or steam may result in an intermittent pressure increase / decrease resulting in the leak occuring only intermittently making the source of contamination more difficult to trace.
  • 3. Pasteurizer plate heat exchangers require crack testing at least once per annum by a specialist crack / leak testing company.
  • 4. Crack testing methods can vary and do not require regulatory approvals making some testing methods questionable e.g. ultrasound. The most well established / reliable and trusted methods are the gas test where helium is introduced into the milk side and a sensitive "sniffer" detector is placed in the pressurixsed side. Another methoud is the dye penetrant test for heat exchanger leaks. This involves stripping down the heat exchanger and coating every plate with a dye penetrant,, rinsing irt off and then using a UV Light to detect any dye remaining in pinholes.Some companies use ultrasonic testing which in my experience can be unreliable.
  • Where steam is used then there is a tendency for burn on the plates which reduces run times, can cause scorched particle contamination and will also result in the formation of heavy bioflilms where heat resisitant spores can multiply.
  • Stripping a large heat exchanger down to check for leaks or to clean burn on deposits can be very time consuming and often results in damage to plate rubbers which can be stuck to each other and damaged.
  • The plate heat exchanger needs to be pressurised / closed to a given size which may reduce with frequent opening / closing and reducing the efficiency of the plant.
  • Renewing plate gaskets can be very costly and also time consuming resulting in plant down time.
    • NOTE -- not complete April 2019 --- update in progress

      3. UHT

      Indirect tube in tube heat exchanger.

      4. UHT

      Indirect coiled tube heat exchanger.

      5. UHT

      Indirect plate heat exchanger.

      6. UHT

      Scraped Surface heat exchanger.

      7. Near UHT

      Steam infusion.

      Holding time should be be validated / checked annually (www.easytest.biz) and also heat exchangers should be checked for cracks on an annual basis.

      Note: all information on this website is for interest only and is not to be relied upon



      For more information or to discuss your requirements please contact us.

John Watson
Office: +44 1224 861 507
Mobile: +44 7931 776 499
jw@dairyconsultant.co.uk

We are a longstanding member of the Society of Dairy Technology and have Fellowship of the Institute of Food Science and Technology.
Member of the Society of Dairy Technology and have Fellowship of the Institute of Food Science and Technology IOD

 

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Office: +44 1224 861 507
Mobile: +44 7931 776 499
jw@dairyconsultant.co.uk

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