This is KaminiDeol from Bangalore and i have a shop to sell cake but whenever electricity has gone our home made cake gone melt some one kindly tell me how can i make my cake last longer?

You do not say what type of cakes you are selling or what frosting.  I know a lot of cream is used in your country.  There is no way that I know to extend the life of a cake frosted and/or filled with cream without refrigeration.  The most heat stable frosting of which I know is American Buttercream made with shortening instead of butter, but even that will not hold up to heat but a short period of time.

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