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The present experiments were conducted to determine the kinetics of cooling rates (with respect to time) and firmness changes of pineapple fruits during un-steady state cooling before ripening the fruits. Pineapple fruits were cooled down from about 23.50C to 5.30C to enable them suitable for the pre-cooling chamber. 1.0 Metric Ton of pineapple placed in perforated plastic crates was cooled first to the desired optimum temperature of the ripening. Out of this, randomly selected 15 kg of pineapple fruits were taken for the experimental investigations. The cooling process during un-steady state is fitted to three mathematical models, viz. linear, exponential, polynomial equations. Polynomial second-order equation is found for the best fit between experimental and predicted values with R2 value of 0.997. The firmness also changes during the un-steady state it can be measured with penetrometer. the highest correlation coefficients were found from a polynomial second-order equation with R2 of 0.985. The experimental readings show that the consumable pineapple fruit firmness is 2.4 kg/cm2. These artificial ripening of pineapple fruits gives good structure and color and the data collected could be useful for the design of higher capacity fruit cooling equipment and also for preserving fruits for a longer period.