Autoclaves and retorts

Autoclave and retort are two names for pressure cooking vessels used in food manufacturing to sterilise canned food and in later versions by engineering firms to cure rubber tyres. The starting point was known as a steam digester, attributed to French scientist Denis Papin, in 1679.

The hazards of working with steam under pressure very quickly became apparent and Papin devised a safety valve to mitigate the risk of explosion, leading many to refer to it as the Papin digester. It was called a digester because it was generally used to apply heat and pressure to bones, leaving cooked bones soft and friable for bonemeal. Other processes were developed for this piece of equipment, from which Papin developed a prototype steam engine. This was subsequently developed into the static steam engines built by Thomas Newcomen.

Chevalier-Appert, a nephew of Nicolas, invented the first reliable pressure gauge for retorts and autoclaves in 1852. This was an essential accessory to prevent explosions and standardise the process. Early retorts comprised a steel vessel, with a metal basket to hold filled bottles or cans. Later versions were fitted with systems that allowed product to be rotated as it cooked, reducing the cooking time. To start a cooking cycle, the vessel is loaded and the door closed. Steam is brought into the cooking chamber and the contents cooked for the required time at the necessary temperature. Once cooked, the steam was turned off and the retort allowed to cool.

A cooking cycle can last for hours, not finishing until the centre of the load had been subjected to a predetermined temperature and for a set period of time. The result is overcooked product on the outside to be sure that the centre cooked properly. Later refinements include automated loading, a key advance to raising throughput.

The Shaka principle

The next milestone, in the late twentieth century, was reached by Richard Walden, a process engineer working for Carnaud-Metalbox. Convinced that it was time to make retorts more efficient, he devised what is now referred to as the Shaka retort, which shakes its load backwards and forwards, driven by a reciprocating actuator at speeds of more than 100 cycles per minute.

Richard Walden

It was clear from the outset that when the prototype reached a certain speed, the load underwent a quantum cooking effect, a “sonic boom” for food, so to speak. Depending on the consistency of the product, cooking time went down dramatically. Further details are available here:

Walden fixed the amplitude on the prototype at around 150mm and varied the speed or rpm on reciprocating arm. For any given product viscosity, Walden could identify a threshold at which a quantum heat transfer took place in the cooking vessel. Further increases in the rpm had no significant effect on cooking times.

John Emanuel signed up manufacturers

Shaka is an undisputed milestone achievement, but has yet to persuade mainstream food manufacturers to scale down their investments in energy-hungry retort lines. The technology has been licensed to two retort manufacturers, Steriflow in France and Allpax in the USA. Prototype, pilot and production models are all available. Although the Shaka units are smaller than their conventional counterparts, they can achieve the same throughput with multiple shorter cooking cycles.

A revolution in the making

The Appertisation of food launched a slew of events that led us to greet the dawn of industrialisation. In the early years of the French revolution, confiseur Nicolas Appert standardised a process that was doubtless known to many at that time. Appert’s single-minded work on heat treating sealed jars, bottles and metal canisters occupied him for years. He filled notebooks and diaries with his observations, recording in minute detail the empirical foundations of his research. Nicolas Appert was a member of the revolutionary Lombard section, radical protesters who took to the streets of Paris at moments of high tension in the French revolution.

A confiseur is a cook who prepares a range of savoury and sweet dishes that have been given long slow cooking until the food almost turns to mush. The standard equipment in a confiseur’s workshop of the time was a copper of boiling water and seasonal ingredients. Today, the word confiserie refers to boiled sugar confectionery, although it probably covered a wider range of foodstuffs in Appert’s day. Most of the confiseur’s stock lines were sealed with a layer of fat and had no shelf life to speak of.

However, Appert’s sealed bottles could be stored with increasing reliability. This “time travel for food”was a pivotal discovery for the future of urban life. As word spread of Appert’s achievements spread across the French capital, Appert was awarded a substantial sum in gold coins, on condition that he put his method into the public domain. A copy of Appert’s instructions reached Bordeaux wine merchant Pierre Durand, who promptly patented the idea in England. As an early trader in intellectual property, Durand struck a number of deals, including one with engineer Bryan Donkin in Bermondsey. The events that followed are covered elsewhere in this blog, in a short story.

The development of Appertisation as a commercial process led to a scaling up of the cooking process. What started out as a hot water bath was reworked as an autoclave or retort. In 1852, one of Nicolas Appert’s nephews, Raymond Chevalier-Appert patented a key component for an retort — a manometer or pressure gauge.

Canned goods coming a cropper?

We have been used to seeing cheap canned foods on supermarket shelves all the year round for decades. With southern Europe just one of the many regions suffering record temperatures and drought around the world, it is timely to look at the possible impact on food products that we have relied on for centuries. It is necessary to distinguish canned foods that have an underlying seasonality, in other words, a point in the season at which the given food is plentiful.

Foods such as canned peeled plum tomatoes, canned salmon, or canned green beans, are packed during the peak cropping weeks of the season. Dedicated canning and cooking lines operate 24/7, with a scaled up version of a process that Nicolas Appert would recognise instantly. In the case of wild salmon, the canneries are located next to the rivers and are stocked up with empty cans ahead of the season. When the salmon return to spawn, fishing crews join the serried ranks of predators that are attracted by thousands of fish in breeding condition.

The standard cooking unit on such lines are a large tank of water, similar to a swimming pool, but kept at a rolling boil for the duration of the pack, which can last weeks. As the fish are caught and brought to a salmon cannery, they are prepared and the cans are filled before cooking. The duration of the cooking time is regulated by a crawler belt that covers the floor of the cooker. Small 100 gram cans are shifted through the cooker during the day at relatively rapid speeds, since they need less cooking than larger cans.

In the case of peeled plum tomato canneries, can sizes go up to 3kg. Lorryloads of raw tomatoes are delivered during the day, some of which will be kept for the night shift. When they clock in, they start filling 3kg cans while the crawler belt is slowed down to its slowest setting. By the time the day shift returns, there will be large stacks of packed and cooked 3kg cans. There will also be a steady stream of lorries laden with tomatoes for the day shift as the belt at the bottom of the cooking tank returns to its daytime setting.

This kind of production line depends on high volume intakes during a clearly-delimited number of weeks (salmon canneries generally pack more than one kind of salmon). It is vulnerable to seasonal variations and crop failures. A bit like us, really. There is an important distinction to make for peeled plum tomatoes, which is that these are mainly grown and packed in Italy. Unlike chopped tomatoes or tomato paste or passata, the cannery can only pack intact tomatoes. These are an industrial variety that are not useful for any other product.

Footnote on the protagonists in Time Travel for Food

Leadership is something we all respond to and it takes many forms.

Take a figure from history, such as Napoleon Bonaparte. A product of the ruling elite of his day, Napoleon underwent officer training and was undaunted by meeting calls to define the working structure of a post revolutionary state from scratch. The Codes Civils (sometimes referred to as the Napoleonic Codes) were an object lesson in structuring the edifice of a state at the start of a post-royal era ( Bonaparte had the outward signs of a civic visionary and expected to lead from the front.

Employing a completely different set of skills, Nicolas Appert perfected the system of sealing food into bottles or cans and cooking it so thoroughly that the product would keep indefinitely. Sometimes referred to eponymously as Appertisation, the process has been used with very few changes, for more than two hundred years. Appert predated fellow Frenchman Louis Pasteur by just over 60 years and would not have predicted the link between heat treatment and killing pathogens that Pasteur would make in years to come.(

There are grounds to suppose that the Appertisation process was known to food producers, but not widely practiced in the 1790s. In place of a theoretical explanation for the incontrovertable success of the process, Appert constantly ran tests on batches of food, using bottles and stoppers of all sorts of material: ceramic, glass and metal. As the years progressed, his confidence in the process grew, as he learnt what cooking times different foods needed in a water jacket of boiling water. Nicolas Appert had been raised by an inn keeper working in Chalons-sur-Saone and was a competent chef. His entire working life was focussed on feeding people and by the 1790s Appert was working as a confiseur in a Paris suburb.

A confiseur is someone who cooks off food, usually with boiling water, to make range of “confits” or foods almost cooked to a mush. Confiserie refers to boiled sugar confectionery, while confits are table-ready dishes which can be sweet or savoury and typically capped off with a layer of fat. The aim is to cook off seasonal gluts, although meat-based confits had short shelf lives, since the melted grease did not offer any real protection to the dish. This was the reason for Appert’s interest in sealing his wide-necked bottles, in a bid to extend shelf life. Appert successfully got reliable results, which is why Appertisation is referred to as “Time Travel For Food” on this website.

Appert plied his trade as a confiseur and wholesale grocery from a workshop in rue des Lombards. He was a member of the militant Section des Lombards, who mobilised at moments of crisis during the revolution in Paris. An active Jacobin, Nicolas and his wife Elisabeth supported the revolutionary cause in practical ways, such as holding planning meetings in the workshop.

As readers will learn in the short history of Nicolas Appert, the confiseur was pulled into the Jacobin Terreur, saved only by the fact that Robespierre was executed 36 hours before Appert was due to go to the scaffold. The Appert household survive the latter years of the revolution: Nicolas is awarded an “encouragement” of 12,000 gold coins by Napoleon. This comes with a requirement to publish a manual to Appertisation at his own expense. Appert remained politically active during his life and was elected mayor of Ivry-sur-Seine.

Appert also makes a trip to England in 1814, at the height of the Napoleonic wars. The reason for the trip was for after-sales support for an English engineer who had licenced the process for commercial exploitation. The technology transfer had been overseen by Pierre Durand, a Bordeaux wine merchant turned intellectual property agent. Durand’s leadership style was simply blunt and overbearing. He met his match, however, in Bryan Donkin, his English client.

A highly regarded engineer, Donkin had undertaken  work for the Fourdrinier brothers, Henri and Seely, to make their purchase of a design for a papermaking machine work in a paper mill environment. As his French clients faced bankruptcy and Donkin still had a workshop to keep in production, there was a pause in proceedings during which Donkin tried to stake a claim on what is known today as the Fourdrinier papermaking machine. Resourceful as ever, Donkin contrived to settle the name of the machine on the brothers, but retained control over the crucial detail that allowed him to  sell working papermaking machines in his own name. Since he installed almost 200 machines across Europe, one can suppose that he was commercially successful. It should be added that Donkin also patented the dip pen and a number of nib designs, which generated far greater sales than could be earned from selling a papermaking machine. This management style is close to opportunistic, but shows a high level of resourceful thinking. Bryan Donkin’s grandson, called Bryan after his grandfather, developed and patented the Donkin gas valve, which is more widely known than Donkin senior’s achievements.

Packing them in

An unmistakeable sign of the impending holiday season turned up this morning in the form of an email from Thierry Jourdan, boss of the family-run cannery La Quiberonnaise in Britanny. Founded in 1921 by Thierry’s grandfather, the fish canning business packs sardines and mackerel landed by local inshore boats as well as taking in yellowfin tuna to pack a range of cans in domestic sizes.

Such canneries were a common sight in seaside towns during the first half of the twentieth century. Today, there are still a number of survivors in what used to be a crowded market. As the fleets dispersed and catches waned, the importance of the tourist trade was recognised by canneries along the French coast. The 1930s saw the establishment of paid summer holidays for French workers: it was the salvation of resourceful canners.

They greeted holidaymakers with open arms and tasteful souvenirs. Local artists are still engaged to create designs for annual editions of elaborately decorated cans of fish, with the promise of a fresh series the next year. Themes range from gently humorous picture postcard subjects to classical offerings that are as likely to end up in an art gallery as a kitchen. Canned fish as an art form has some unexpectedly well-known devotees. Food critic Jean-Luc Petitrenaud always takes a decorated can of sardines for his host whenever he is invited to dinner.

Fighting brands

With household budgets increasingly under pressure, cheaper options are under constant review. There is a case to be made for arguing that the fixed costs of running a canning line or a filling line is much the same regardless of the price of the finished product. But the variations that can arise from the quality of the ingredients remain significant.

Sometime referred to as “fighting brands”, cheap canned goods with obscure branding are planned into quiet moments of the production schedule, taking up the slack towards the end of a tomato season, for instance. Recognisable from their lightweight tinplate-lined cans, the fighting brands are very unlikely to be fitted with ring pulls.

Branded goods are judged on the quality of the finished product, for which we expect to pay more. Fighting brands will find ways of extending the product, which represents a greater share of the final price. 

Time travel for food

The process of sealing food into a glass jar or a can and boiling the sealed units has been used for over two centuries. In 1812 French revolutionary Nicolas Appert published a user’s manual to the process, called The Art Of Preserving for Several Years Animal and Vegetable Substances. The process is often referred to eponymously as Appertisation and the food is literally cooked in the can (or bottle).

Appert was making and selling bottled vegetables and other foodstuffs in Paris, during the dark days of the terror and Robespierre. Ever since the French revolution, canned food has sustained earnest adventurers atop the highest mountain peaks, in the depths of the oceans, not forgetting orbiting space stations.

Although first published in French, within months English translations were being studied in England and the technique was applied to preserve food for long sea voyages. A French naval captain complained that this was a French military secret which had been smuggled across the Channel and was now being used against its inventors.

The reality was in fact more mundane. English engineer Bryan Donkin ran a workshop in Bermondsey, London and was looking for an additional manufacturing activity to stay in business. Donkin licensed Appert’s process from a travelling commercial agent who went by the name Peter Durand in England and Pierre Durand in France. Donkin set to work filling tinplate canisters with food, only to find that he had missed something out.

Donkin summoned Durand, who called Appert away from the wreckage of his house and workshop to visit Donkin in Bermondsey during 1814. The problem was simple enough: the food was not being sealed in its cans until it had cooled down, by which time there was a risk of spoilage.

By the time Appert left England, Durand had a fully working filling line and Appert had seen at first hand just how effective tinplate canisters were for storing food. The quality of tinplate available in France was nowhere near as good as the tinplate Donkin was buying. Nevertheless, by paying over the odds for tinplate, Appert started to use metal packaging for his products.

Originally from the Champagne region of France, Appert was used to packing food in heavy glass jars. These were not well-received by the French navy, on the grounds of breakage, and needed more attention when sealing the jars and keeping out the air. Appert spent the rest of his life experimenting with canned and bottled food until he reached the age of 91, dying in poverty and obscurity during 1841.

Read a short story about Nicolas Appert