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The Generalized Chaplygin Gas (GCG) model is characterized by the equation ofstate $P = -A \rho^{-\alpha}$, where $A>0$ and $\alpha < 1$. The model has beenextensively studied due to its interesting properties and applicability inseveral contexts, from late-time acceleration to primordial inflation.Nonetheless we show that the inflationary slow-roll regime cannot be satisfiedby most of the parameter space of the GCG model when General Relativity (GR) isconsidered. In particular, although the model has been applied to inflationwith $0 < \alpha < 1$, we show that for $-1 < \alpha \le 1$ there is noexpansion of the Universe but an accelerated contraction. For $\alpha \le-5/3$, the second slow-roll parameter $\eta_H$ is larger than unity, so thereis no sustained period of inflation. Only for $\alpha$ very close to -1 themodel produces enough $e$-folds, thus greatly reducing its parameter space.Moreover, we show that the model is ruled out by the Planck 2018 results.Finally, we extend our analysis to the Generalized Chaplygin-Jacobi Gas (GCJG)model. We find that the introduction of a new parameter does not change theprevious results. We thus conclude that the violation of the slow-rollconditions is a generic feature of the GCG and GCJG models during inflationwhen GR is considered and that the models are ruled out by the Planck 2018results.

No slow-roll inflation \`a la Generalized Chaplygin Gas in General Relativity