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Ultra-high temperature processing (UHT), ultra-heat treatment, or ultra-pasteurization is a
food processing
Food processing is the transformation of agricultural products into food, or of one form of food into other forms. Food processing includes many forms of processing foods, from grinding grain to make raw flour to home cooking to complex industr ...
technology that
sterilizes liquid food by heating it above – the temperature required to kill bacterial
endospore
An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., no ...
s – for 2 to 5 seconds. UHT is most commonly used in milk production, but the process is also used for fruit juices, cream, soy milk, yogurt, wine, soups, honey, and stews.
UHT milk was first developed in the 1960s and became generally available for consumption in the 1970s.
The heat used during the UHT process can cause
Maillard browning
The Maillard reaction ( ; ) is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor. Seared steaks, fried dumplings, cookies and other kinds of biscuits, breads, toasted marshmallows, and ma ...
and change the taste and smell of dairy products.
An alternative process is
flash pasteurization
Flash pasteurization, also called "high-temperature short-time" (HTST) processing, is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, wine, and some dairy products such as milk. Compared with other ...
, in which the milk is heated to for at least 15 seconds.
UHT milk packaged in a sterile container has a typical unrefrigerated
shelf life
Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a ...
of six to nine months. In contrast, flash pasteurized milk has a shelf life of about two weeks from processing, or about one week from being put on sale and, some can even last to many months.
[
]
History
The most commonly applied technique to provide a safe and shelf-stable milk is heat treatment. The first system involving indirect heating with continuous flow ( for 6 min) was manufactured in 1893. In 1912, a continuous-flow, direct-heating method of mixing steam with milk at temperatures of was patented. However, without commercially available aseptic packaging systems to pack and store the product, such technology was not very useful in itself, and further development was stalled until the 1950s. In 1953, APV pioneered a steam injection technology, involving direct injection of steam through a specially designed nozzle which raises the product temperature instantly, under brand name Uperiser; milk was packaged in sterile cans. In the 1960s APV launched the first commercial steam infusion system under the Palarisator brand name.
In Sweden, Tetra Pak
Tetra Pak is a Swedish–Swiss multinational food packaging and processing company with head offices in Lund, Sweden, and Pully, Switzerland. The company offers packaging, filling machines and processing for dairy, beverages, cheese, ice cream ...
launched tetrahedral paperboard cartons in 1952. They made a commercial breakthrough in the 1960s, after technological advances, combining carton assembling and aseptic packaging technologies, followed by international expansion. In aseptic processing, the product and the package are sterilized separately and then combined and sealed in a sterile atmosphere, in contrast to canning, where product and package are first combined and then sterilized.
The Importation of Milk Act 1983 was passed by the UK Parliament
The Parliament of the United Kingdom is the supreme legislative body of the United Kingdom, the Crown Dependencies and the British Overseas Territories. It meets at the Palace of Westminster, London. It alone possesses legislative supremac ...
following a successful appeal to the European Court of Justice
The European Court of Justice (ECJ, french: Cour de Justice européenne), formally just the Court of Justice, is the supreme court of the European Union in matters of European Union law. As a part of the Court of Justice of the European Un ...
that prevented the government from banning the importation of UHT milk.
In June 1993, Parmalat
Parmalat S.p.A. is a dairy and food corporation which is a subsidiary of French multinational company Lactalis. It was founded by Calisto Tanzi in 1961.
Having become the leading global company in the production of long-life milk using ultra-h ...
introduced its UHT milk to the United States. In the American market, consumers are uneasy about consuming milk that is not delivered under refrigeration, and reluctant to buy it. To combat this, Parmalat is selling its UHT milk in old-fashioned containers, unnecessarily sold from the refrigerator aisle. UHT milk is also used for many dairy products.
In 2008 the UK government proposed to produce 9 pints out of every 10 as UHT by 2020 which they believed would significantly cut the need for refrigeration, and thus benefit the environment by reducing greenhouse gas emissions
Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and lar ...
. However the milk industry opposed this, and the proposition was abandoned.
Technology
Ultra-high-temperature processing is performed in complex production plants, which perform several stages of food processing and packaging automatically and in succession:
* Flash heating
* Flash cooling
* Homogenization
* Aseptic packaging
In the heating stage, the treated liquid is first pre-heated to a noncritical temperature ( for milk), and then quickly heated to the temperature required by the process. There are two types of heating technologies: ''direct'', where the product is put in a direct contact with the hot steam, and ''indirect'', where the product and the heating medium remain separated by the equipment's contact surfaces. The main goals of the design, both from product quality and from efficiency standpoints, are to maintain the high product temperature for the shortest period possible, and to ensure that the temperature is evenly distributed throughout.
Direct heating systems
Direct systems have the advantage that the product is held at a high temperature for a shorter period of time, thereby reducing the thermal damage for sensitive products such as milk. There are two groups of direct systems:[
* Injection-based, where the high-pressure steam is injected into the liquid. It allows fast heating and cooling, but is only suitable for some products. As the product comes in contact with the hot nozzle, there is a possibility of local overheating.
* Infusion-based, where the liquid is pumped through a nozzle into a chamber with high-pressure steam at a relatively low concentration, providing a large surface contact area. This method achieves near-instantaneous heating and cooling and even distribution of temperature, avoiding local overheating. It is suitable for liquids of both low and high ]viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
.
Indirect heating systems
In indirect systems, the product is heated by a solid heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
similar to those used for pasteurization. However, as higher temperatures are applied, it is necessary to employ higher pressures in order to prevent boiling.[ There are three types of exchangers in use:][
* Plate exchangers,
* Tubular exchangers
* Scraped-surface exchangers.
For higher efficiency, pressurized water or steam is used as the medium for heating the exchangers themselves, accompanied with a regeneration unit which allows reuse of the medium and energy saving.][
]
Flash cooling
After heating, the hot product is passed to a holding tube and then to a vacuum chamber
A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump. This results in a low-pressure environment within the chamber, commonly referred to as a vacuum. A vacuum environment allows researchers to con ...
, where it suddenly loses the temperature and vaporizes. The process, referred to as ''flash cooling'', reduces the risk of thermal damage, inactivates thermophilic microbes due to abruptly falling temperatures, removes some or all of the excess water obtained through the contact with steam, and removes some of the volatile compounds which negatively affect product quality. The cooling rate and quantity of water removed is determined by the level of vacuum, which must be carefully calibrated.[
]
Homogenization
Homogenization is part of the process specifically for milk. Homogenization is a mechanical treatment which results in a reduction of the size, and an increase in the number and total surface area, of fat globules in the milk. This reduces milk's tendency to form cream at the surface, and on contact with containers enhances its stability and makes it more palatable for consumers.
Worldwide use
UHT milk has seen large success in much of Europe, where across the continent 7 out of 10 people drink it regularly.[Solomon. Zaichkowsky, Polegato.''Consumer Behavior'': Pearson, Toronto. 2005. p. 39] In countries with a warmer climate such as Spain, UHT milk is preferred due to the high cost of refrigerated transportation and "inefficient cool cabinets". UHT is less popular in Northern Europe and Scandinavia, particularly in Denmark, Finland, Norway, Sweden, the United Kingdom and Ireland. It is also less popular in Greece, where fresh pasteurized milk is the most popular.
While most regular milk sold in the United States is pasteurized, a significant share of organic milk sold in the US is UHT treated (organic milk is produced at fewer locations and consequently spends more time in the supply chain and could therefore spoil before or shortly after being sold if pasteurized).
Nutritive effects
UHT milk contains the same number of calorie
The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of on ...
s and calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
as pasteurized milk
Pasteurization or pasteurisation is a process of food preservation in which packaged and non-packaged foods (such as milk and fruit juices) are treated with mild heat, usually to less than , to eliminate pathogens and extend shelf life.
T ...
. Some loss of vitamin B12, vitamin C
Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) an ...
and thiamin
Thiamine, also known as thiamin and vitamin B1, is a vitamin, an essential micronutrient, that cannot be made in the body. It is found in food and commercially synthesized to be a dietary supplement or medication. Phosphorylated forms of thia ...
can occur in UHT milk. UHT milk contains 1 μg of folate
Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and ...
per 100 g, while pasteurized milk contains 9 μg.
UHT milk's protein structure is different from that of pasteurized milk
Pasteurization or pasteurisation is a process of food preservation in which packaged and non-packaged foods (such as milk and fruit juices) are treated with mild heat, usually to less than , to eliminate pathogens and extend shelf life.
T ...
, which prevents it from separating in cheese making.
Two studies published in the late 20th century showed that UHT treatment causes proteins contained in the milk to unfold and flatten, and the formerly "buried" sulfhydryl (SH) groups, which are normally masked in the natural protein, cause extremely-cooked or burnt flavours to appear to the human palate. One study reduced the thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
content by immobilizing sulfhydryl oxidase
In biochemistry, an oxidase is an enzyme that catalyzes oxidation-reduction reactions, especially one involving dioxygen (O2) as the electron acceptor. In reactions involving donation of a hydrogen atom, oxygen is reduced to water (H2O) or hydro ...
in UHT-heated skim milk and reported, after enzymatic oxidation
Browning is the process of food turning brown due to the chemical reactions that take place within. The process of browning is one of the chemical reactions that take place in food chemistry and represents an interesting research topic regardin ...
, an improved flavor. Two US authors prior to heating added the flavonoid
Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans.
Chemically, flavonoids ...
compound epicatechin
Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids.
The name of the catechin chemical family derives from ''catechu'', which is the tannic ...
to the milk, and reported a partial reduction of thermally generated aromas.
See also
* Aseptic processing
Aseptic processing is a processing technique wherein commercially thermally sterilized liquid products (typically food or pharmaceutical) are packaged into previously sterilized containers under sterile conditions to produce shelf-stable products ...
* Food preservation
Food preservation includes processes that make food more resistant to microorganism growth and slow the oxidation of fats. This slows down the decomposition and rancidification process. Food preservation may also include processes that inhibit ...
* Food storage
Food storage is a way of decreasing the variability of the food supply in the face of natural, inevitable variability. p.507 It allows food to be eaten for some time (typically weeks to months) after harvest rather than solely immediately. I ...
* Food packaging
Food packaging is a packaging system specifically designed for food and represents one of the most important aspects among the processes involved in the food industry, as it provides protection from chemical, biological and physical alterations ...
* Food engineering
* Pasteurization
Pasteurization or pasteurisation is a process of food preservation in which packaged and non-packaged foods (such as milk and fruit juices) are treated with mild heat, usually to less than , to eliminate pathogens and extend shelf life.
The ...
* Flash pasteurization
Flash pasteurization, also called "high-temperature short-time" (HTST) processing, is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, wine, and some dairy products such as milk. Compared with other ...
References
External links
Milk in a Box. From: Interesting Thing of the Day
{{DEFAULTSORT:Ultra-High-Temperature Processing
Food preservation
Milk
Pasteurized foods
History of agriculture in the United Kingdom
Agricultural health and safety
Food law