As an archaeobotanist, an archaeologist specialised in studying plant remains found in archaeological excavations, I aim to reconstruct and interpret the relationships between humans and plants in the past. Archaeological plant remains, also known as subfossil plant remains, help us to reconstruct the former landscape and inform us how humans exploited it and even transformed the vegetation. Archaeobotanists do not necessarily study one time period, nor a specific region or topic. They can study plant remains from the Palaeolithic or the 20th century, and everything in between. They can focus on one specific site, work across the country or continent, and even work worldwide. They can delve into topics such as natural vegetation, forestation, domestication, trade, food consumption and much more. The one thing that all of this has in common is the link between humans and plants. But most archaeobotanists do specialize, most notably in the plant parts they study, such as fruits, seeds, pollen, wood or phytoliths. And most archaeobotanists have a beloved time period, favourite region or topic that they find most intriguing. In my case my research focuses on early modern Dutch urban food consumption.
I study what people ate in early modern Dutch cities, and how this changed through time. The best way to study what people ate in the past, is to look at their excrement and kitchen refuse, both of which can be found in the archaeologists treasure trove: the cesspit. These latrines were used to empty one’s bowels, but also served as a place to discard kitchen refuse and household waste. The content of a cesspit consists of organic remains from plants and animals, inorganic (culinary) material culture such as earthenware, glassware and ceramics, but also wooden cups and plates, as well as (decorative) objects, personal belongings and much, much more.
The content of an archaeobotanical cesspit sample consists of, among others, floral remains in different shapes and sizes (Figure 1). The items are sorted with the use of a microscope (Figure 2) and identified on a species level (and sometimes even on the level of species variety) by using a reference collection (Figure 3). The Groningen Institute of Archaeology offers a wonderful digital, open access, reference collection, see https://www.plantatlas.eu/.
When the content of a cesspit sample is analysed, sorted and identified, the interpretation begins. What can these plant remains tell us about past human-plant relationships? Most plant species are interpreted in a standardized way: wild plants inform us about the vegetation composition, make-up of soils and hydrology, whilst agricultural weeds in particular inform us about the crops grown and their local, regional, international or even global provenance. Wild but poisonous or toxic plants inform us about potential medicinal applications. A majority of plant species found in cesspits are classified as economic plants, grown as a food crop or cultivated for other useful purposes, such as fibres for textiles or seeds for oil. Identifying edible plants helps us better understand what plants people used for food and which parts people consumed. It also helps us better understand how food was prepared in the past, as preparation marks can be left behind on seeds and fruits.
Some preparation marks are easier to identify than others: nuts need to be cracked to get to the seed; apple seeds may be sliced when cutting up an apple, cereals can be ground, resulting into fragmented bran. But sometimes the archaeobotanist finds fragmented plant parts that, at a first glance, do not make sense.
I have come across dozens and sometimes hundreds (or even more) cherry stones and plum stones in a single cesspit sample. No surprise there, cherries and plums were grown in local orchards, sold in the market and consumed with gusto. Most of these stones will have been discarded in the cesspit as a result from eating the fruits and spitting out the stones, or after de-pitting the fruits for dinner preparation. Only a small percentage is assumed to have been accidentally swallowed and secreted as excrement. Still, archaeobotanists find many fragments of cherry and plum stones (Figure 4). This is something that raises questions when you think about it. Why would these sturdy fruit stones be fragmented? A more pressing question when you are aware that the Rosaceae family, among others also including almond, peach, and even apple, contains – to varying degrees – hydrocyanic acid, also known as hydrogen cyanide and sometimes called prussic acid. The seed coat and fruit wall protects the consumer from digesting this acid, which can be poisonous when consumed. So why would someone break the stones of these fruits?
To test the assumption that cherry stones were fragmented intentionally, and not through, for instance, pressure, an experiment was devised. Cherries were bought at the farmer’s market and taken to a physics lab to measure the pressure required to fragment the stones. After a number of tests, the calculated force to fragment a cherry stone averaged 23,9 kg or 239 Newton (Graph 1). This makes it more plausible that the stones were intentionally fragmented, as opposed to – for instance – fragmentation due to soil pressure.
Consulting early modern cookbooks provided me with a list of recipes requiring the cook to de-stone cherries for the preparation of jams, sauces, syrups and tarts. Delicious experiments ensued, but I did not manage to fragment cherry stones whilst cutting and de-stoning, pressing through a cloth or colander, or by just baking the fruit with stones in a tart in the oven. Working a batch of cherries with a mortar and pestle did the job, though. But than you would have to pick the fragmented stones from the mushy cherries: not ideal at all. Picking up the eighteenth century encyclopaedia compiled by Noël Chomel gave me the hint I needed. In the Dutch version of his Dictionnaire œconomique (Algemeen huishoudelijk-, natuur-, zedekundig- en konst- woordenboek), he mentions different recipes for preparing cherries. Two recipes for cherry liquor instruct the reader to fragment the cherry stones by using a mortar and pestle (Figure 5). The fragmented fruits, including the stones and (I assume) the seeds are added to the brandy (Dutch: brandewijn) and, after closing the bottle, the mixture is put in the sun to infuse. Adding spices such as cinnamon, cloves and sugar is optional, according to the author.
So, it is plausible that the fragmented cherry stones found in early modern cesspits are the result of the domestic production of cherry liquor. Other fruits, such as plums and peaches, are also used to make a fruity liquor according to Chomel’s encyclopedia. However, what happens to the acid contained in the seeds? That requires further research. It might be that the prescribed infusing in the sunlight helps denature the acid into harmless molecules, leaving only the (bitter) taste behind. This line of research will be undertaken come summer with the aid of a brewer and some chemical analysis. In the meantime, a cherry and cinnamon flavoured lemonade is my poison of choice. Bottoms up!