The light cream, sweetened condensed milk and chocolate sauce in a homemade Irish cream recipe need to be refrigerated to prevent bacterial growth. Bacteria can cause food poisoning or at least turn the cream and milk sour through a build-up of lactic acid. According to Foodsafety.gov, bacteria can grow in perishable foods such as light cream if left out at room temperature for just two hours.

Light cream will keep in a refrigerator set between 35 and 40 degrees Fahrenheit for a week. While you can store unopened condensed milk at room temperature for many weeks, once opened it needs refrigeration. Even in a refrigerator, condensed milk will go off after a week. However, the alcohol content of Irish cream does help to prevent bacterial growth. This prolongs the length of time you can keep the drink refrigerated. For example, the BBC suggests that homemade Irish cream will remain safe to drink for up to two months if refrigerated.

Refrigeration is only half the battle in keeping Irish cream fresh. The other challenge lies in safe bottling. The beverage should be stored in a sterilized glass or plastic bottle with a screw-cap for easy sealing. The easiest way to sterilize bottles at home is to put them in a dishwasher set to the highest temperature. If you use glass bottles, put them in the oven at 325 degrees F after washing for faster drying. After that, the bottles are ready to be filled with Irish cream and placed immediately into the refrigerator.

You may notice that the labels on commercially produced Irish cream do not always recommend refrigeration. For example, Bailey's Irish Cream, one of the best-selling global brands, suggests keeping the bottle in a cool, dry place -- whether unopened or opened. However, this is partly because the professional manufacturing process combines the cream and alcohol in such a way that the alcohol acts as an effective preservative. While the same principle applies to homemade Irish cream, the process is different and the preservative effect less reliable.