The present study was undertaken with the objectives to determine the shelf life of the prepared product and to estimate the cost of the production. Four different ratio of WPC @ 5%, 10%, 15%, 20% and different holding times 10, 15, 20, 25 minutes for fermentation of batter were used in the present study. Product was tested for yeast and mould count, standard plate count, coliform count and cost of the product was also worked out for different treatment combinations. The data obtained during investigation were statistically analysed by using two way classification and Critical Difference (CD) technique between treatments. The highest average yeast and mould count/gm of idli samples 37.83 was recorded on day fifteen. The highest average SPC/103gm of idli samples 52.61 was recorded on day fifteen. The coliform count is negative which means that strict hygienic practice was observed during preparation of idli. The highest cost of the idli sample T4H3 is Rs. 26.70 as compared to the other treatments. Result revealed that the microbial analysis of the prepared product is equally good, free from yeast and mould, standard plate count and coliform and is safe for consumption.