The growth lag phase during microbial fermentation reduced productivity and equipment efficiency. Inoculum age and size were the two important variables considered in fermentation optimisation. Previous studies investigated these two variables separately, in contrast to the orthogonal or use of response surface modelling method by recent papers. In nearly all cases, the inoculum from the late exponential or early stationary phase was selected as optimal. In the current study, the authors optimised inoculum conditions using a strategy that combined inoculum age and size as inoculum cell number to shorten the lag phase in yeast cultivation. Inoculum from the middle exponential phase (7th h) exhibited priority in activity and adaptability. This condition was confirmed by inoculating the resuspended cell sediments into fresh potato dextrose medium. The results indicate that biomass (cell number for single cell microbes and wet/dry cell weight for filamentous strains), rather than inoculum age and size, should be considered during inoculum condition optimisation.Key words: Fermentation, optimisation, cell number, exponential phase, inoculum age, inoculum size.