August 14, 2014 at 1:00 am

Ask a cook

How long does my homemade mayonnaise keep?

Homemade mayonnaise recipes say you should use it in three days. I keep it sometimes for six weeks. What am I risking?

You are risking food-borne illness. Commercial mayonnaises are made with ingredients that have a specific level of acidity that inhibit the growth of bacteria.

Homemade mayonnaise doesnt keep as long for several reasons. For one, you probably used fresh lemon juice, which may be lower or higher in acidity than bottled lemon juice. There may not be enough to slow bacterial growth.

Next, you handled all the ingredients the eggs when you cracked them, the lemon when you squeezed it, the mayonnaise when you moved it to a container. You could have introduced a slight amount of bacteria. Given enough time and exposure to higher temperatures, that slight amount will have time to grow into a lot.

Finally, youre taking the mayonnaise in and out of the refrigerator without tracking how long its been at room temperature. The two-hour rule, the time that food can be between 40 and 140 degrees before bacteria begins to grow, is cumulative. Every time you take it out of the refrigerator while you use it, youre adding to the amount of time it has been exposed, giving bacteria plenty of time to multiply.

Email questions about food and cooking to Kathleen Purvis at kpurvis@charlotteobserver.com.