Is the white coating on grapes safe? Experts explain its benefits

Ever noticed a powdery white film on your grapes and wondered if they've gone bad? That coating, far from being mold, is a natural and beneficial layer called bloom.

What Is Bloom?
According to viticulture expert Hans Walter-Peterson, bloom is a natural wax secreted by the grapes themselves. It acts as a protective shield, helping to prevent water from collecting on the fruit and slowing down moisture loss, which keeps the grapes from drying out too quickly. This natural barrier also helps protect against pathogens.

Health Benefits and Identification
Bloom isn't just a protective layer—it's also good for you. The primary component, oleanolic acid, has been shown to have antibacterial, anti-inflammatory, and antioxidant properties. A study from ScienceDirect highlighted that this compound can also support cell and cardiovascular health.

It's easy to mistake bloom for mold, but there are key differences:

Bloom is an even, powdery white or slightly greenish coating on the entire grape.

Mold appears in fuzzy, brown, or patchy spots, usually on grapes that are already shriveled or decayed.

Tips for Storing and Washing Grapes
To keep your grapes fresh and preserve their beneficial bloom, experts offer a few tips:

Don't wash them until you're ready to eat them. Washing grapes before storing them can damage the bloom, which in turn encourages mold growth and shortens their shelf life.

Store them properly. The University of Michigan recommends storing grapes in the refrigerator at 0–4°C (32–39°F) in a ventilated bag or container. Registered dietitian Theresa Gentile suggests keeping them in the back of the crisper drawer, which is the coldest spot.

Keep them separate. Grapes should not be stored near produce that releases ethylene gas, such as apples, avocados, or tomatoes, as this will accelerate ripening and spoilage.

Inspect them. To prevent decay from spreading, remove any grapes that look like they are starting to rot before you store the rest.