The increased work of separation due to remixing partially separated streams within countercurrent recycle cascades, W(unmix), was calculated and compared with the absolute minimum thermodynamic work, W(min), required to effect a given separation. Remixing can occur in all countercurrent constant recycle cascades regardless of whether a separation process is potentially reversible, partially reversible, or irreversible in nature, or whether the cascade is composed of double entry or single entry stages. In an ideal cascade (IC), the remixing of materials with different compositions is eliminated and the sum of the stagewise separative work, W(sep), is identically equal to W(min) based on the overall separation occurring across the cascade, or W(sep) = W(min). However, in the constant recycle cascade (CRC) the work of separation is greater than the thermodynamic minimum by an amount equal to W(mix) due to remixing of partially separated streams, or W(sep) = W(min) + W(unmix). By comparison, the separative work due to remixing is lost or wasted in the CRC. The lost work, W(unmix), can be a significant contribution to the energy requirements of countercurrent recycle cascades since it becomes infinite at both extremes of reflux; the minimum recycle ratio, RR(min), and total recycle, RR(total). Consequently, W(unmix) goes through a minimum at some point in between the two limiting extremes of recycle ratio in a constant recycle cascade. For the examples considered in this analysis, W(unmix) in the CRCs goes through a minimum at recycle ratios of 1.32, 1.35, and 1.53 times the minimum recycle (RR(min)) for separation factors of alpha = 1.027, 1.067, and 1.20, respectively. At these "Optimal" recycle ratios (i.e.. minimum W(unmix)), the work of separation is increased by about 28 to 31% over the thermodynamic minimum. Finally, many of the perceived differences in the analysis of separation cascades for the partially reversible, potentially reversible, and irreversible processes disappear when mixing within the CRC is taken into account.