Why Do Blueberries Have a White Powdery Coating? (It's Bloom)

Why Do Blueberries Have a White Powdery Coating?

The white powdery coating on blueberries is called bloom. It is a natural wax that the berry produces itself, and it is a good sign — it means the berries are fresh and have not been handled too much. Bloom is not mould, not pesticide residue, and not something you need to wash off with any urgency. It is there for a reason, and the plant put a lot of energy into making it.

Bloom is made of tiny crystals of epicuticular wax — a waxy layer produced by the epidermal cells of the berry skin. The wax is extruded through the skin and forms a microscopically crystalline layer that scatters light, which is why it looks white and powdery rather than glossy and clear. The same kind of wax appears on grapes, plums, and apples, but blueberries show it particularly well because their skin is dark and the contrast is high. See our grape guide for more on the bloom on grape skins.

What Bloom Does

Bloom is a protective barrier. The wax layer serves several functions that help the berry survive in the wild and stay fresh after harvest. First, it is a water repellent. The waxy surface causes rain and dew to bead up and roll off rather than soaking into the skin, which would make the berry prone to cracking and rot. This is why fresh blueberries look dry even after light rain in the field.

Second, bloom is a barrier to gases. Berries continue to respire after they are picked, taking in oxygen and releasing carbon dioxide and water vapour. The wax layer slows this gas exchange, which slows dehydration and extends shelf life. Without the wax, berries would lose moisture faster and shrivel sooner.

Third, bloom has antimicrobial properties. The wax contains compounds that inhibit the growth of mould and bacteria on the skin surface. This is part of why berries with intact bloom last longer in the fridge than berries that have been rubbed or washed aggressively. And fourth, the light-scattering white colour may help reflect UV light and protect the underlying tissue from sun damage while the berry is still on the bush.

Bloom Is a Freshness Indicator

Because bloom is a delicate surface layer, it wears off with handling. Every time a berry is touched, rolled, or jostled, some of the wax crystals are rubbed away. A punnet of blueberries with a strong, uniform white bloom has been handled gently and is recently picked. A punnet that looks shiny and dark, with little or no visible bloom, has been sitting around longer or has been through more handling.

This is a useful quick test in the shop. If you see two punnets at Woolworths or Coles and one has obvious bloom while the other looks shiny, pick the one with the bloom. It will be fresher, firmer, and last longer at home. If you want a more thorough check, scan the punnet with PickFresh — the freshness score reflects these same surface and texture indicators.

The same rule applies to grapes. A fresh grape bunch has a visible white bloom, and a bunch that has been handled heavily has lost it. See our blueberry season guide for when blueberries are at their best in Australia.

Bloom Is Not Mould

One of the most common questions people ask is whether the white powder is mould. It is not. Mould on blueberries looks different: it is fuzzy, thread-like, and usually grey-blue or greenish-white. Bloom is uniformly powdery, sits flat against the skin, and does not have hair-like structures. Mould also tends to appear in patches, often near a damaged or leaking berry, while bloom covers the whole berry evenly.

If you see a berry with a fuzzy growth, that is mould and that berry should be discarded. The surrounding berries may still be fine if they are firm and dry — see our mould safety guide for the rules on when to salvage and when to discard. But the white, powdery, even coating on a healthy blueberry is bloom and is nothing to worry about.

Should You Wash Blueberries Before Eating?

Wash blueberries right before you eat them, not before you store them. Rinsing removes the bloom and wets the surface, both of which shorten shelf life. Once the bloom is washed off, the berries lose their protective water-repellent layer and absorb moisture, which makes them more prone to mould and splitting.

If you prefer to rinse produce for pesticide reduction, do it just before eating. A gentle rinse under cold running water is sufficient. You do not need a produce wash or a vinegar soak for blueberries — the bloom comes off easily and the skin is thin enough that harsh washing damages the berries. For storage, keep unwashed blueberries in their original punnet in the fridge and wash only what you plan to eat.

If you are freezing blueberries, you can skip washing before freezing and wash after thawing. See our blueberry freezing guide for the full method — they retain over 90% of their antioxidants when frozen.

The Nutritional Side of Bloom

Bloom itself is not particularly nutritious — it is mostly long-chain waxes, which your body does not digest. But the presence of bloom is correlated with higher antioxidant levels in the underlying skin. The same compounds that give blueberries their dark colour (anthocyanins) are concentrated in the skin, and intact bloom means the skin has not been damaged, which means those antioxidants are preserved.

Blueberries are one of the highest-antioxidant foods available, and most of those antioxidants are in the skin. So eating blueberries with the bloom intact is a good way to maximise the nutritional benefit. See our blueberry serving guide for portion sizes and nutrition breakdown, and our vitamin C guide for how blueberries compare to other antioxidant-rich produce.

What to Look for When Buying Blueberries

Look for a strong, even white bloom across the punnet. The berries should be firm, plump, and deep blue with no red or green patches (those are underripe). Avoid punnets with leaking juice, mouldy berries, or berries that look shrivelled. A fresh blueberry should roll freely in the punnet when you tilt it gently — stuck-together berries are often leaking or mouldy.

Frozen blueberries are a great alternative when fresh are out of season. They are picked at peak ripeness and retain similar antioxidant levels. See our blueberry season guide for when to buy fresh versus frozen in Australia. And if you want to confirm freshness before buying, scan the punnet with PickFresh.