Professor Robert B Heimann | Culinary Craftmanship: The Evolution of Pottery for Cooking

Cooking food is arguably one of the most important transitions in human evolution, and initiated hundreds of thousands of years of refinement in both technique and technology. Professor Emeritus Robert B Heimann of TU Bergakademie Freiberg, Germany, recently reviewed the evidence for early cooking vessels and tracks the evolution of their production, identifying important strategies of optimisation using various natural materials, firing methods, and designs to improve durability, functionality, and efficiency over time.

The Importance of Cooking

In modern society, cooking is such a routine part of daily life that we rarely pause to consider its significance. The controlled use of fire for cooking began at least 800,000 years ago with an ancient human relative, Homo erectus. As our ancestors transitioned to a diet of softer, cooked food, their tooth size and jaw shape gradually became smaller and more refined. For a long time, cooking methods were quite rudimentary and would have primarily involved open fires.

Despite its apparent simplicity, the practice of cooking in open fires helped reduce the risk of food poisoning from scavenged meat and also made food easier to digest, increasing the energy gained from such meals. Arguably, increased food energy consumption triggered the growth of neurons in the brain and, thus, advanced the cognitive evolution of ancient humans.

Over time, cooking techniques became more advanced, and archaeologists have uncovered evidence of pottery, including cooking pots, from Chinese caves dating back approximately 20,000 years. In his 2024 review paper, ‘Ancient and historical cooking pots and food: an eternal communion. A topical review’, Professor Robert B Heimann discussed key mechanical and thermal properties of ceramic cooking vessels, highlighting the strategies of property optimisation.

Pottery Through Time

Before pottery, people cooked using campfires, hot stones, and natural containers like animal stomachs or turtle shells. Some practices involved wrapping foods such as meat and vegetables in clay and baking them in campfire embers, while others dropped heat stones in clay-lined pits to boil food in. Various groups across the globe developed independent methods to cook food. For instance, in North America, Indigenous people roasted food by placing ignited wood charcoal into mesh baskets covered in clay, while in Australia, earth ovens were common.

However, true cooking requires durable, fireproof vessels. The mass production of cooking pots began in Neolithic Mesopotamia, expanding the possibilities of cooking to include sauces, breads and gravies, in addition to the processing of cereals. Boiling food in pots enhanced flavour, texture, and nutrient retention while also allowing for more diverse and complex meals. The earliest recorded recipes, written on Mesopotamian clay tablets in cuneiform Akkadian script, highlight the cultural significance of cooking.

Cooking pots revolutionised food preparation by enabling controlled heat, reducing contamination, preserving nutrients, and allowing food to be boiled, retaining vital fats from meat that frying in a campfire would otherwise lose. Across the globe, different cultures developed unique styles, from Roman and Chinese vessels to North African tajines. In medieval Europe, tripod pots became common. They were designed to raise the vessel above the heat source, which not only reduced thermal stress on the pot but also improved heat distribution and prevented food scorching.

However, Professor Heimann acknowledges that despite its advantages, it is contested by some that the original function of pottery was for cooking. Nevertheless, certainly, by Middle Neolithic times (5800–5300 BCE), there is evidence that pottery had become essential to food preparation, marking a major shift in humanity’s relationship with food.

1. Chinese tripod cooking pot. Reproduced under a CC BY-NC-SA 4.0 licence
2. Mesopotamian cooking vessels from Tell Halaf (6th/5th millennium BCE). © Staatliche Museen zu Berlin, Germany.
3. Medieval glazed tripod cooking pot. © The Trustees of theBritish Museum. Reproduced under a CC BY-NC-SA-4.0 licence.
4. Modern Chinese shaguo cooking vessels. Reproduced under a CC BY-SA 2.0 licence.

The Chemistry of Cooking and Clay

Cooking is essentially a chemical process that utilises heat to transform the basic components of food, such as proteins, carbohydrates, and fats, into forms that are easier to digest. Proteins begin to break down at lower temperatures (less than 100°C), and between 140–170°C, a chemical reaction called the Maillard reaction occurs, producing a range of flavour compounds that give foods their characteristic taste when fried, baked, or grilled. At higher temperatures above 170°C, potentially harmful compounds like acrylamide from proteins can form, and fats can break down into acrolein.

Cooking in durable ceramic pots helps further break down food by providing even and controlled heat. The performance of these cooking vessels relies on their ability to withstand changes in temperature without cracking. The key factors that affect their performance include the type of clay used (whether it contains calcium carbonate or not), the temper (i.e., materials like sand or limestone added to strengthen the pot) and their grain size, the firing temperature used in its production, and the thickness of the pot’s walls. A well-made pot needs to balance its strength, heat resistance, and durability to ensure it can handle the stresses of cooking.

Crafting Pottery from Nature’s Materials

As previously mentioned, the type of clay used in pottery influences the properties of the final product. Noncalcareous clay (one that contains very little calcium carbonate), such as Nile mud in Egypt, expands less with heat, making it more durable than calcareous clays, such as those from Mesopotamia. However, adding temper materials like limestone or mussel shells improves heat resistance. This technique has been utilised by Indigenous Mississippian potters, who used burned mussel shells to strengthen pots, preventing cracks and, thus, improving durability. The shells helped bind the clay, reducing plasticity and increasing toughness. The alkaline environment produced by the shells also improved the cooking of maize by enhancing flavour and increasing nutrient availability, helping to prevent vitamin deficiencies like pellagra.

Firing temperature also influences the properties of the final product. At higher temperatures, clay particles fuse together more tightly, a process called sintering, producing a denser pot. However, ceramic pots made from coarse materials by the Mississippian potters were fired at low temperatures (800–950°C). This made them porous, which helped them resist cracking under heat by allowing expansion. The pores also held moisture when soaked in water, which turned to steam during cooking, producing juicy and tender food. However, too much porosity both reduced heat conductivity and caused hygiene issues by allowing food particles, such as fats, to penetrate the walls. To prevent this, potters smoothed the inside surfaces of the pots with resin, tar, clay slips or glazes to seal the pores. This practice is first attributed to the Mesopotamian potters. Observed in the work of ancient Middle Minoan (Kamares ware), Greek (Attic red-on-black ware), and Roman (Terra sigillata) potters, the practice can still be seen today.

While higher firing temperatures and less temper improved pot strength, more temper and lower temperatures were needed for thermal stress resistance. The shape of temper grains also affected durability, with flat particles providing better strength than rounded ones. While thinner pot walls reduced thermal stress, they nevertheless weakened the pot, decreasing its durability. Thus, the art of producing optimum ancient ceramic cooking pots required a careful balance.

The Recipe for a Perfect Pot

So, what makes the ideal ceramic cooking pot? Well, as Professor Heimann states, there is no perfect pot, as the choice of materials and production process have conflicting outcomes. However, what archaeological evidence tells us is that ancient potters were resourceful above anything else and used the most readily available materials at their disposal. Nowadays, most cooking pots we are familiar with are made of metal. The use of this material originated as bronze in Roman times, transitioning to cast iron in ancient China. Copper and brass cooking pots were introduced in 18^th-century Europe, and stainless steel ones in the early 1900s. Although producing a larger disconnect from our natural world, metal pots are stronger, heat up more evenly, and are more hygienic than clay pots. While a far cry from the rudimentary methods of Homo erectus, modern culinary practices would not be what they are today without the centuries of innovation and refinement that have shaped cooking tools, techniques, and materials.