In the early recipe hummus kasa, vinegar is used instead of lemon.
The recipe appears in Muhammad bin Hasan al-Baghdadi’s medieval Book of Dishes, a work associated with the culinary tradition of 13th- and 14th-century Cairo. It combines puréed chickpeas with tahini and uses vinegar to provide acidity rather than the lemon juice familiar in most modern hummus.
This hummus kasa was considerably more elaborate than many contemporary versions. Historical descriptions mention spices, herbs, and nuts, and the preparation could be rolled out and left to sit overnight. It also lacked garlic, another ingredient now strongly associated with hummus.
The recipe is easy to misread because lemon is now the standard acidic ingredient in many hummus preparations. Verjuice, tamarind, and yogurt all occur in Middle Eastern culinary traditions, but they are not the acid specified for this particular hummus kasa recipe. The variation shows that medieval chickpea dishes were not yet standardized.