A juice and soup company in Curitiba, Brazil, wants to take its best-selling smooth vegetable soup national. The technical team has put four routes on the table: keep pasteurising and chilling, switch to UHT and aseptic cartons, retort the soup in pouches, or treat it with high pressure. Each route changes the shelf life, the taste, the pack, the cost and the words allowed on the label. The pasteurisation vs UHT vs HPP decision, with retorting as the fourth option, is one of the most commercial choices a food business makes, and it starts with what each process can and cannot kill.
In short
- Pasteurisation (for milk, 72 °C for 15 s or 63 °C for 30 min) kills vegetative pathogens but not bacterial spores, so most pasteurised products are chilled and last days to a few weeks.
- UHT heats liquids to about 135 to 150 °C for a few seconds and packs them aseptically. The product is commercially sterile and keeps for months at room temperature until opened.
- Retorting heats food after it is sealed. Low-acid foods need at least F0 3 minutes, the 12D botulinum cook, and keep for a year or more, with the most cooked flavour.
- HPP holds packed food at typically 400 to 600 MPa for a few minutes at chilled temperature. Flavour stays close to fresh, but spores survive, so low-acid HPP foods must stay refrigerated.
- The right choice depends on pH, storage, shelf life, pack, volume and taste, proven by trials.
Pasteurisation vs UHT vs HPP: what is the difference?
The four processes differ in what they kill, how they kill it and when the pack is sealed. Pasteurisation and HPP kill vegetative microbes but leave bacterial spores alive, so the food also needs chilling, acidity or another hurdle. UHT and retorting destroy spores and give commercially sterile food that keeps at room temperature.
Two terms matter. A spore is a tough, dormant form made by some bacteria, such as Clostridium botulinum, that survives heat which kills vegetative (actively growing) cells. Commercial sterility means the food contains no microorganisms able to grow in it under normal, unrefrigerated storage; it is not absolute sterility.
| Pasteurised | UHT | Retorted | HPP | |
|---|---|---|---|---|
| How it works | Mild heat | Very high heat for seconds, then aseptic filling | Heat under pressure after sealing | Water pressure on the sealed pack |
| Typical conditions | Milk: 72 °C for 15 s or 63 °C for 30 min | About 135 to 150 °C for a few seconds | Low-acid foods: at least F0 3 min | Typically 400 to 600 MPa for a few minutes, chilled |
| Kills spores? | No | Yes | Yes | No |
| Storage | Chilled | Ambient until opened | Ambient | Chilled |
| Typical shelf life | Days to a few weeks | Several months | A year or more | Weeks, set by trials |
| Taste and texture | Close to fresh | Slightly cooked | Most changed | Very close to fresh |
| Main cost drivers | Cold chain, short dates, waste | Aseptic line, sterile packs | Retort energy, cans or pouches | Costly batch equipment or tolling, cold chain |
What does pasteurisation do, and how long does it last?
Pasteurisation is a mild heat treatment that destroys the vegetative pathogens likely to be present and many spoilage organisms, while accepting that bacterial spores survive. For milk the reference conditions are 72 °C for 15 seconds in a continuous high-temperature short-time (HTST) system, or 63 °C for 30 minutes in the low-temperature long-time (LTLT) batch method. National rules set their own requirements, so check your national legislation.
These conditions were designed to destroy the most heat-resistant non-spore-forming pathogens historically linked to raw milk, Mycobacterium tuberculosis and Coxiella burnetii, so Salmonella, Listeria and Campylobacter are destroyed with a margin. A flow diversion valve returns any milk that has not reached temperature. Because spores and some heat-tolerant spoilage bacteria survive, pasteurised milk is kept at 5 °C or below and lasts days to a few weeks, depending on raw milk quality, plant hygiene and the cold chain.
Acidity changes the picture. Fruit juices with a pH of 4.6 or below are pasteurised, often at higher temperatures, to deal with yeasts, moulds and enzymes. Because C. botulinum cannot grow in them, hot-filled or aseptically packed acid juices can be shelf-stable at room temperature after pasteurisation alone. To understand why spores and pH matter so much, Food Science for Non-Scientists covers the microbiology in plain language.
How does UHT give months of shelf life without a fridge?
UHT (ultra-high temperature) processing heats a liquid to about 135 to 150 °C for a few seconds, cools it and fills it into sterile packs in a sterile zone, a step called aseptic packaging. The heat destroys spores as well as vegetative cells, so the sealed product is commercially sterile and keeps for several months at room temperature until opened.
Why so short a time? As temperature rises, microbes are killed much faster than flavour, colour and vitamins are damaged, so a few seconds at around 140 °C can deliver as much spore kill as several minutes at 121 °C. Plants heat the product either indirectly, through a stainless steel plate or tube wall, or directly, by injecting culinary steam and then removing the added water under vacuum. Direct heating gives less cooked flavour but costs more to run.
The trade-offs: a slightly cooked taste in milk, mainly from sulphur compounds released when whey proteins are heated; expensive aseptic lines that need careful validation; and total dependence on pack integrity. The prize: no cold chain until opening, lower distribution energy, and access to markets where refrigeration is unreliable.
What is retorting, and why do low-acid foods need a botulinum cook?
Retorting is in-container sterilisation: food is sealed in a can, jar or pouch and then heated under pressure, typically at around 115 to 125 °C, until it is commercially sterile. Low-acid foods, with a pH above 4.6 and a water activity above 0.85, must receive a botulinum cook: a 12D reduction of C. botulinum spores, equivalent to a minimum F0 of 3 minutes at the slowest-heating point.
Worked example
The D-value is the time at a fixed temperature that kills 90 % of a population (one log). For C. botulinum spores at 121.1 °C, D is about 0.21 min.
A 12D process needs 12 × 0.21 min = 2.52 min at 121.1 °C. The industry minimum is rounded up to F0 = 3 min, where F0 is the process lethality expressed as equivalent minutes at 121.1 °C.
If every can started with one spore, a 12D process would leave a survival probability of 10⁻¹², one can in a million million.
The z-value is the temperature change that alters the D-value tenfold; for these spores it is 10 °C. So every 10 °C drop makes killing ten times slower: one minute at 111.1 °C counts as only 0.1 min at 121.1 °C, so reaching F0 3 min at that temperature takes 3 ÷ 0.1 = 30 minutes.
Many commercial processes deliver well above F0 3 min to control heat-resistant spoilage spores.
Acid foods with a pH of 4.6 or below, such as canned peaches or pineapple, need far milder processes, often at or below 100 °C. Retorted products keep for a year or more at ambient temperature, but long heating softens texture, darkens colour and gives a “canned” flavour. Thin retort pouches heat through faster than cans, so they usually need shorter processes. Process times are set by thermal process specialists using heat penetration tests, and any change of recipe, fill weight or pack size needs re-validation.
What does HPP do, and why does HPP food still need refrigeration?
High pressure processing (HPP) holds food, already sealed in a flexible pack, in a water-filled vessel at typically 400 to 600 MPa for a few minutes, usually at chilled temperature. It kills vegetative bacteria, yeasts and moulds, including pathogens such as Listeria, Salmonella and pathogenic E. coli when properly validated, while flavour, colour and many vitamins stay close to fresh.
For scale, 600 MPa is about 6,000 times atmospheric pressure and more than five times the pressure at the deepest point of the ocean. The pressure acts equally in all directions at once, so the pack keeps its shape and there is no cold spot. Packs must be flexible plastic, such as PET bottles or pouches; glass and metal cannot be used, and foods with air pockets are crushed.
The key limit: at chilled or ambient temperatures HPP does not inactivate bacterial spores, and some enzymes resist pressure. An acidic HPP juice is protected by its pH as well as the cold. A low-acid HPP product, such as a soup or cooked meat, must stay refrigerated, and its shelf life must be set with non-proteolytic C. botulinum in mind, because that organism can grow from about 3 °C in low-oxygen packs. HPP vessels are expensive and run in batches, so many brands pay a contract (toll) processor per kilogram and truck product to and from its site.
How do you choose between pasteurisation, UHT, retort and HPP?
Start from the product’s pH and the shelf you want it on, then work through cost, pack and taste:
- Check pH and water activity. Acid foods (pH 4.6 or below) have more options. Low-acid foods stored at ambient need UHT or retorting with a validated botulinum cook.
- Decide chilled or ambient. Moving a chilled product to an ambient shelf means a new process and pack, and often a new factory, not a label change.
- Set the shelf life and the evidence. Plan storage trials, challenge tests for chilled foods and process validation before promising a date to a customer.
- Check the pack. UHT needs aseptic cartons or bottles, retorting needs cans, jars or retortable pouches, and HPP needs flexible plastic.
- Test the taste. A slightly cooked note may be acceptable in long-life milk but not in a premium juice.
- Cost the whole route. Include equipment or toll fees, packaging, energy, cold chain, waste from short dates and minimum volumes.
- Agree claims early. Words such as “fresh”, “natural”, “raw” and “unprocessed” are restricted or open to challenge in many markets.
For the Brazilian soup, HPP keeps the fresh taste but needs chilling and a validated life; UHT or a retort pouch gives months on an ambient shelf with a more cooked flavour. Food Technology for Non-Technical Professionals works through this kind of decision as a case study.
Frequently asked questions
Is UHT milk less nutritious than pasteurised milk?
Only slightly. Protein, calcium and most minerals are essentially unchanged by UHT treatment. Losses of some heat-sensitive vitamins, such as thiamin, vitamin B12 and folate, are a little higher than in pasteurised milk, and small further losses can occur during long storage. For most diets the difference is minor. The bigger practical differences between the two milks are flavour, storage and shelf life.
Does HPP kill all bacteria?
No. HPP at chilled or ambient temperature kills vegetative bacteria, yeasts and moulds, including common pathogens when the process is validated, but it does not inactivate bacterial spores, and some enzymes survive. That is why HPP juices, dips, soups and cooked meats carry “keep refrigerated” instructions and limited shelf lives. Combining pressure with high temperature can inactivate spores, but that is not standard commercial HPP.
How long does UHT milk last after opening?
Once opened, UHT milk is no longer commercially sterile, so treat it like fresh milk: keep it in the fridge at 5 °C or below and use it within the time stated on the pack, usually a few days. Microbes from the air, hands and the pouring spout get in as soon as the seal is broken, and nothing in the milk stops them growing once it is opened.
Can HPP juice be labelled “fresh” or “raw”?
It depends on the market. Codex sets the principle that labels must not be false or misleading, and national rules decide whether HPP-treated products may use words such as “fresh”, “raw” or “unpasteurised”. Rules differ between countries, and some restrict “fresh” to foods that have not been processed or preserved. Check your national legislation before the artwork is approved, and never imply that refrigeration is unnecessary.
Why is canned food safe for years without preservatives?
Because the retort process destroys the spores that could grow in it, and the hermetic seal keeps new microbes out. Low-acid canned foods receive at least the equivalent of F0 3 minutes, a 12D reduction of Clostridium botulinum spores. While the seam or seal stays intact, nothing in the can is able to grow during normal storage. Swollen, leaking or badly dented cans should be rejected.
Next step. Food Technology for Non-Technical Professionals explains, without jargon, what pasteurised, UHT, sterilised, HPP, freeze-dried and extruded really mean for safety, shelf life, taste, cost and claims, and how shelf life and date marks are set. It ends with a proctored final assessment and an ASC certificate. You can also see all eleven food science and technology courses.
Sources. P. J. Fellows, Food Processing Technology: Principles and Practice, 5th edition (Woodhead Publishing, 2022); R. Paul Singh and Dennis R. Heldman, Introduction to Food Engineering, 5th edition (Academic Press, 2014); Codex Alimentarius Commission, Code of Hygienic Practice for Milk and Milk Products, CXC 57-2004, Code of Hygienic Practice for Low and Acidified Low Acid Canned Foods, CXC 23-1979, and General Standard for the Labelling of Prepackaged Foods, CXS 1-1985; US Food and Drug Administration, guidance on low-acid canned foods and juice processing.
This article is general guidance on food processing methods and is not a substitute for the applicable standard, your national legislation or the advice of a qualified food safety professional.