Lime or limestone (an abundant sedimentary rock) has found great use in construction throughout history. The usage of lime in construction dates back to some of the world’s earliest settlements. Even though some experts estimate the usage of lime in mortar started at least 10,000 years ago, radiocarbon dating of lime mortar found in early Neolithic settlements in Nevali Çori (Turkey) would suggest an even earlier use, going back more than 20,000 years. The irony is that we cannot really date Nevali Çori that far back.
The “lime cycle” is a well-known property of lime that enables its use in construction. It is a three-step process:
Calcination: CaCO3(s) + Heat → CaO(s) + CO2(g)
Hydration: CaO(s) + H2O(l) → Ca(OH)2(s) + Heat
Carbonation: Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(g)
During the first step, calcium carbonate (in limestone) is heated to produce calcium oxide (burnt lime, or quicklime). The second step is the hydration of lime. Upon contact with water, burnt lime produces a strong base: calcium hydroxide (aptly named as slaked lime). The third and final step is carbonation. The slaked lime in water (limewater) comes into contact with carbon dioxide and reverts to its original form: calcium carbonate. This cycle has been essential in the invention of lime mortar. In order to produce the mortar, slaked lime in water is mixed with some aggregate (e.g., sand). Upon its application, the carbonation step is triggered by the atmospheric carbon dioxide to complete the cycle, forming calcium carbonate.
While lime-based mortar must have been an integral part of building many kitchens throughout history, usage of lime in the kitchen has not been limited to construction alone. It has traditionally been used as a key ingredient in numerous food preparations. Out of many of its culinary uses, I will focus on two distinct recipes originating in two regions far away from each other.
Our first recipe utilizes a technique from ancient Mesoamerica: Nixtamalization. “Nixtamalización” is the name of the process that is used for the preparation of maize. Passed from generation to generation, this ancient technique is still used around the world today for various maize products, tortilla being a popular one. The process uses slaked lime or limestone in boiling water. The usage of lime not only softens the maize, so it can be ground easily to create a dough, but it is also helpful in terms of food safety as it destroys almost all the aflatoxin in mycotoxin-contaminated produce. The treatment also uncovers additional nutritional value by making more essential amino acids available. During their research into the food safety aspects of the traditional nixtamalization process, Dr. Doralinda Guzmán-de-Peña studied their family recipe. The recipe relayed here outlines the basic steps of the technique that has been used in Mexican homes traditionally:
(1) Boil maize (1 kg) with water (3 l) and limestone or slaked lime (10 g) for 50 min; (2) Soak the mixture overnight (14 h); (3) Wash the cooked maize two or three times with water and (4) Ground nixtamal to obtain the dough (masa). Once the dough is ready, different dishes can be prepared: tortillas, tamales, atole, gorditas, etc.
Our second recipe is for Pekmez. It is, in essence, a molasses-like reduction of grape juice. Instead of grapes, it could also be made using other fruit rich in sugars. Traditionally, the version that uses grapes has been prepared in Turkey almost unchanged for ages. The earliest written accounts of pekmez date back to Divan-i Lugati’t-Türk, written in 1073. Similar to how it is used in nixtamalization, lime is also used to make pekmez. The function of lime in this process is two-fold: 1) it reduces the acidity of the grape juice, 2) it also aids in clarifying the syrup by adsorbing impurities. The traditional recipe uses limestone soil called “pekmez toprağı” (pekmez soil) rich in calcium carbonate. Based on the oral tradition, many families – including mine – prepare it more or less using the same method. Here is a recipe relayed by Dr. Selma Birer from their paper on the dietary use of pekmez in Turkey:
The grapes harvested from the vineyards are washed, have their stems separated, and juiced by being pressed in crushing mills. The excess water is evaporated by boiling. In order to prevent the acidity (sourness) of the grape juice, white soil called pekmez soil containing 90% or more CaCO3 (calcium carbonate) is used. Besides entirely or partially removing the juice’s acidity, the soil also helps clarify it. Pekmez soil is added in the ratio of 0.1-1 kg to 100 kg of juice. When the pekmez soil is added to the reduction, it is boiled for 5-10 minutes and then rested for clarification. pH change, temperature, and positively charged calcium ions play a role in this chemical process.
Even though archeological evidence has not yet been established about its history, the recipe for pekmez made from grapes is believed to have originated in prehistoric Anatolia. If we were to compare the two grape-based products, pekmez must have been even more critical for neolithic communities than wine, especially when we consider its function to preserve the nutritional value of the grapes.
Our ancestors must have understood and experimented with the lime cycle, enabling the recipes discussed above. The discovery of the lime cycle had its use both in culinary and construction applications. A hypothesis on how this could all have started comes via another ancient culinary practice: stone boiling. Stone boiling is the practice of transferring heat via heated stones instead of direct heat from open fire to the cooking vessel. Large stones would be heated in a fire or hearth and then placed in the cooking liquid. More stones would gradually be introduced in order to sustain the cooking process. According to this hypothesis, the discovery of the lime cycle could have “accidentally” been ignited by using limestones for this purpose. Limestones heated in a wood fire would get hot enough to start the calcination process described above. The cook would then naturally notice how these stones changed when heated and reacted with water. Being curious, they would also not have missed how it hardened over time and reverted to a stone-like material: reshaped limestone.
Contemporary recipes for pekmez and nixtamalization do not call for heated limestones. However, archeological and experimental evidence suggests that using limestones for stone boiling can facilitate the cooking and start the required molecular reactions for nixtamalization. It could be possible that the innovation of lime mortar in construction was not the only happy result of the accidental use of limestones for cooking. Due to lack of evidence suggesting otherwise (yet), we should accept that limestones found their initial use in construction. Nevertheless, we also need to appreciate their incidental use in cooking (through stone boiling). Observations on how it altered the cooking results must have followed naturally. It seems to me that the accident of using limestones for cooking might not only have resulted in the discovery of lime mortar in construction, but it could also have resulted in the development of pekmez and nixtamalization.
Utku Can Topçu is a software engineer living in Amsterdam. Next to his day job, he spends most of his time in his kitchen: reading, researching, and experimenting.
 I would like to thank Dr. Inci Gunler for her invaluable feedback during the preparation of this text.
 Dorn Carran, John Hughes, Alick Leslie, Craig Kennedy, “A Short History of the Use of Lime as a Building Material Beyond Europe and North America,” International Journal of Architectural Heritage, 6(2), (2012): 117-146. https://doi.org/10.1080/15583058.2010.511694
 S. Felder-Casagrande, H. G. Wiedemann, A. Reller, “The calcination of limestone – Studies on the past, the presence and the future of a crucial industrial process,” Journal of Thermal Analysis, 49(2), (1997): 971-978. https://doi.org/10.1007/bf01996783
 Carran, A Short History of the Use of Lime
 Doralinda Guzmán-de-Peña, “The Destruction of Aflatoxins in Corn by ‘Nixtamalización,’” in Mahendra Rai, Ajit Varma (eds.), Mycotoxins in Food, Feed and Bioweapons, (Berlin, Heidelberg: Springer, 2009), 39-49. https://doi.org/10.1007/978-3-642-00725-5_3
 Emily C. Ellwood, M. Paul Scott, William D. Lipe, R. G. Matson, John G. Jones, “Stone-boiling maize with limestone: experimental results and implications for nutrition among SE Utah preceramic groups,”Journal of Archaeological Science, 40(1), (2013): 35-44. https://doi.org/10.1016/j.jas.2012.05.044
 Guzmán-de-Peña, “The Destruction of Aflatoxins in Corn by ‘Nixtamalización’”
 Selma Birer, “Pekmezin Beslenmemizdeki Yeri ve Kullanılması,” Beslenme ve Diyet Dergisi, 12, (1982): 107-114. https://beslenmevediyetdergisi.org/ind
 Sevan Nişanyan, “pekmez,” in Nişanyan Sözlük Çağdaş Türkçenin Etimolojisi, https://www.nisanyansozluk.com/kelime/pekmez (accessed on 16 January 2022)
 Birer, “Pekmezin Beslenmemizdeki Yeri ve Kullanılması”
 Ahmet Uhri, Anadolu Mutfak Kültürünün Kökenleri – Arkeolojik, Arkeometrik, Dilsel, Tarihsel ve Etnolojik Veriler Işığında (İstanbul: Ege, 2016), 46-51
 Carran, “A Short History of the Use of Lime”
 Ellwood, “Stone-boiling maize with limestone: experimental results”