The major factor that has notable influence on the outturn of the coffee (the berry to clean coffee weight relation) is the occurrence of fruits with empty seed, which float when put in water. In order to have information on the effect of this kind of fruits on the outturn of the Mundo Novo cultivar, four groups of five samples were prepared each one containing 0, 25, 50, 75 and 100 per cent of fruits with at least one empty seed. Observations were made on the percentage of coffee seed types, flat, peaberry and shell, and also on density, size and weight of flat seeds in order to verify if the abortion of the endosperm, after complete development of the perisperm, would influence these seed characteristics. No difference was noticed on the size, density and weight of the flat seeds. The percentage of peaberry seed decreased with increasing amounts of fruits with empty seeds in the samples, which is due to the fact that very few peaberry fruits float in water. The shell seed percentage, on the contrary, increased in a linear way with increasing numbers of fruits with empty seeds. This may result from a pleiotropic effect of the genetic factor responsible for the abortion of the seed endosperm. The outturn was greatly affected by the increased percentage of floating fruits, which also showed a linear effect on the deterioration of the outturn of the Mundo Novo coffee. The results here discussed on the outturn of the Mundo Novo coffee, pointed out that in the selection of high-yielding coffee trees of this cultivar, individual plants with high incidence of empty seeds must yield at least 24 per cent more ripe fruits than another plant without this defect in order to be selected.