The appearance of small dots or specks on grapes is common, and the source can vary widely. These marks may be harmless features of the fruit’s natural physiology or signal the presence of pests, environmental stress, or a biological infection. Understanding the context of these markings helps determine if the grapes are safe to eat or should be discarded. This guide explains the different origins of these dots.
Dots That Are Completely Normal
Many specks or coatings observed on grapes are natural features that develop as the fruit matures. The most common is “bloom,” a faint, dusty-white layer covering the skin. This bloom is composed of epicuticular wax, a protective layer synthesized by the grape to prevent moisture loss and shield the fruit from ultraviolet radiation. The wax is harmless and may appear uneven or speckled on berries handled roughly during harvest.
Another type of natural dot is the lenticel, which functions as a small pore for gas exchange. Lenticels are minute openings that can sometimes appear as slightly raised or darker spots. They are especially noticeable on varieties with thicker skins or when the fruit is highly mature. These pores are a normal part of the grape’s structure and do not affect the taste or safety of the fruit.
Spots Caused by Fungal Pathogens
When the dots are discolored, sunken, or fuzzy, they often indicate a fungal infection that began while the fruit was still on the vine. This type of infection requires careful attention.
Black Rot
Black Rot starts as small, reddish-brown spots on green berries. These spots quickly enlarge, becoming sunken and black. Eventually, the entire berry shrivels into a hard, dark, raisin-like mummy firmly attached to the stem. This process severely damages the fruit.
Mildews
Other common fungal diseases include the mildews, which present differently based on the specific pathogen. Powdery Mildew initially manifests as a dusty, grayish-white growth covering the surface of the fruit. This can lead to brown, net-like scarring or discoloration on the grape skin underneath. Downy Mildew tends to cause a more general discoloration, leading to a marbled appearance that can progress into a soft, brownish rot.
Botrytis Bunch Rot (Gray Mold)
Botrytis Bunch Rot, often called Gray Mold, typically begins as small, localized brown spots that soften the tissue, frequently starting near the stem attachment point. This infection is aggressive in high-humidity conditions, rapidly spreading across the cluster. It develops a characteristic fuzzy, gray layer of mold over the brown spots. These fungal spots penetrate the skin and compromise the internal structure of the berry.
Marks Left by Pests and Environmental Factors
Sometimes, dots are external markings caused by insects or environmental stressors rather than a penetrating disease.
Pest Damage
Pests like Leafhoppers feed by piercing the grape’s surface cells and sucking out the contents. This action leaves behind tiny, pale stippling marks that resemble fine speckling. These marks are superficial and are considered purely cosmetic damage to the fruit.
Scale insects can leave small, raised, waxy bumps adhered to the berry surface. Pests may also excrete honeydew, a sugary waste product. Honeydew acts as a substrate for sooty mold to grow, resulting in irregular black smudges on the skin. These smudges remain on the surface and can often be rubbed off, distinguishing them from fungal rot.
Residue and Sunburn
External residue from agricultural treatments or washing processes can also mimic dots. Spray residue from fungicides, pesticides, or mineral deposits from hard water can dry into white or colored specks on the skin. Grapes exposed to intense, direct sunlight and high temperatures can develop Sunburn. Sunburn appears as small, localized brownish or bleached spots on the exposed side of the berry.
When to Avoid Eating the Grapes
The safety of consuming grapes with dots depends entirely on the source of the mark. Grapes displaying natural bloom or lenticels are perfectly safe to eat, requiring only a simple rinse if the coating is undesirable. Grapes with light stippling from pest damage or minor spray residue are also safe after thorough washing, as these marks are superficial and do not affect the interior quality.
Caution is necessary when spots indicate disease or pervasive mold. Any grape that is noticeably shriveled, sunken, or has turned into a hard, dry “mummy” due to Black Rot should be discarded immediately. While the occasional infected berry may not pose a severe risk, the potential for certain fungal pathogens to produce mycotoxins makes it advisable to avoid fruit with widespread, soft brown spots or visible, fuzzy gray mold. If only one or two berries show signs of deep fungal infection, it is best practice to remove and discard the entire infected cluster to minimize risk.