Partly or fully deteriorated beans are present in varying amounts in commercial coffee. They seem to have been affected by external agents prior to drying and vary in color from almost normal to black. The experiments reported in this paper were designed to study the influence of the deteriorated beans on the coffee flavor. Samples were secured from the various coffee growing areas of São Paulo: Campinas, Ribeirão Prêto, Mococa, Pindorama, and Vale do Paraíba. Each was hand--graded, the partly or fully deteriorated beans being separated from the normal ones. The normal beans were then mixed with varying amounts of partly or fully deteriorated beans from the same samples. The following blends were prepared for each of the coffee sources: 1 . normal beans only 2. partly deteriorated beans exclusively 3. mixture of normal beans plus 10% in weight of partly deteriorated ones 4. ditto with 20% 5. ditto with 40% 6. ditto with 2.5% of fully deteriorated beans 7. ditto with 5% 8. ditto with 10% The 8 treatments for each source were replicated 4 times, giving thus a total of 256 variables. They were then submitted to an expert coffee-taster for the cup-test. The results obtained indicated that except for the samples from one region (Vale do Paraíba), the others gave always high quality coffee when composed of normal beans only. The addition of increasing amounts of partly deteriorated beans decreased quality correspondingly. The fully deteriorated beans had a still larger impairing effect on the quality. The coffe samples from the Vale do Paraíba gave a poor cup-test (Rio taste) even when they consisted of normal beans only.