In Wallaga, local beer (farso) is one of the most common alcoholic beverages. The beverage is prepared from cereals such as sorghum, millet, maize and barley and an additive plant known as gesho (Rhamnus prinoides). The beer is fermented in a ceramic jar known as huuroo. The brewing process causes pitting in the interior walls. Because most fermentation processes cause pitting of ceramic vessels, use alteration analysis cannot specifically identify past beer brewing practice. Ethnoarchaeological research of beer fermentation in Wallaga shows that in addition to erosion of interior walls of beer jars, the beer fermentation process results in the deposition of residues on the interior walls of the vessels. This residue from beer brewing is different from residue left by other processes because it includes ingredients not incorporated into other foods. As a result, plant microresidue analysis of archaeological ceramics can help to identify past brewing practices and major ingredients of indigenous beer.