The intricacies of modern day food technology make it virtually impossible for anyone but an expert in the field to know whether a processed food is free of any trace of non-kosher ingredients. So all processed foods and eating establishments require certification by a reliable rabbi or kashrut supervision agency.
Check the labels of packaged foods and the kashrut certificates of restaurants and hotels for a copyrighted kashrut symbol like those below.
(Run your mouse over the symbol for information on the certification agencies behind them and click to go the organization's website)
Please note that while these three are the largest kosher certification agencies in the U.S., there are hundreds of other kosher certification agencies – with varying levels of reliability – and each with its own certification symbol. Speak to your rabbi to determine the reliability of a kosher symbol you may encounter.