The present book has been designed to serve the students of microbiology, food microbiology, biotechnology and life sciences. This book tries to meet the need of academics and research both. It provides an introduction to spice essential oils and its effect on heated and unheated cells of food spoilage yeasts. The main emphases are on preservation of thermally processed food products by using synergistic effect of heat treatment and essential oils. The methodology used for this kind of studies is mentioned in detail in this book. The experimental designs and the graphical analysis of data are emphasized throughout to ensure students are equipped to successfully plan their own experiments and examine the results obtained. Therefore this book opens up many new avenues for research directions and applications of essential oil and their constituents in food products.