Is it flour or white mould on buns?

In this brief guide, we are going to answer the question “Is it flour or white mould on buns?”, we are going to look at how to differentiate between both and the potential implications of eating them.

Is it flour or white mould on buns?

To determine whether it is flour or mould on the buns, one needs to have a basic understanding of the visual appearance of mould and flour. If you see a clean and bright white colour, it is flour. Conversely, the colour of moulds is a dirtier shade of white that eventually turns greenish-blue. 

Bread is the product obtained by baking a dough, fermented or not, prepared with wheat flour and/or other flours (usually containing naturally gluten-forming proteins) and water, it may contain other ingredients to produce new formats and flavours.

This product is widely accepted by the population. There is a wide variety of bread. For some types, it is common to sprinkle wheat flour or some other light-colored flour on the surface of the product. This usually leaves the bread with a more rustic appearance, which catches the consumer’s attention.

Sometimes, mould can grow on the surface of buns. These fungi can have a white colour and that is why it is common for the consumer to be in doubt: is it mould or is it just white flour?

How to differentiate mould from flour?

Some tips are valuable to know when it’s mould and when it’s flour:

Scrape the surface of buns

You can use a tool or even your finger to scrape the white spots. If you notice that the material is finely particulate and that these particles come out easily, it’s probably flour.

Smell the buns

The inspection of the suspect bun should be done with care, as the inhalation of fungus spores can be dangerous. A bun having white spots of mould will have a fruity, or a beer-like smell. 

Mould usually alters the quality of buns and may modify its aroma-related attributes. Moulds can be spoilage and/or pathogenic organisms, which during their growth develop unpleasant aromas in buns.

Some fungi release spores that can cause serious respiratory problems, such as asthma or even anaphylactic shock, although the incidence of the latter is uncommon.

Visually inspect the buns

When the white spot is a mould, it can have a velvety appearance (similar to cotton). This is due to the structural part of fungi that is called mycelium.

The flour colour is also an important differentiating factor. Flour has a bright white colour, while mould has an opaque white colour.

Over the days, if the white spots grow, be sure it’s mould and not flour.

What are moulds?

Moulds are a type of fungi. They are a part of the natural environment and can be found almost anywhere where moisture and oxygen are present. They live in the air, soil, plants, animals, and dead or decaying matter.

The development of moulds in food alters the flavour of the products, impairs its quality, and eventually releases mycotoxins.

Mycotoxins are a group of compounds produced by some species of fungi during their growth and can cause serious biological damage when ingested.

What are the most common types of mould that grow on bread?

The fungi that normally grow on buns and give it a mouldy appearance are certain multicellular types that form a filamentous network called the mycelium, which is made up of individual filaments, which are called hyphae.

The most striking feature of fungal mycelia is their coloration. You may have noticed that sometimes moulds of other colours (greenish, bluish, yellowish, reddish, grey, black, or whitish tones) appear on the buns.

 Among the most common types of mould we can highlight:

  • Rhizopus nigricans: produces black spots and white mycelium growth (similar to cotton) – This is the type that is often confused with white flour.
  • Penicillium e Aspergillus sp.:  green-colored fungi.
  •  Neurospora sitophila: purple to pink fungi.

How does mould grow on bread?

Moulds develop on the buns after the baking step, during manipulation of the product in the subsequent operations. This means that the buns were contaminated with fungal spores following the baking process. 

The spores of moulds are abundant in the environment, and upon favourable conditions, they germinate. This means that in damp environments and in the absence of proper ventilation, moulds will start to grow and contaminate the buns.

The temperature of 100ºC, in the centre of the product, is enough to eliminate these microorganisms. This temperature is easily reached during baking.

Then, the contamination may occur as soon as the products leave the oven, during the steps that follow, such as cooling, cutting and packaging, displaying, storing, among others.

The factors that most influence mould development after processing are: temperature and water activity.

Water activity represents the amount of water available for mould growth. Another important factor is humidity, which is closely related to water activity. Humidity represents the amount of water present in the food, but not all of this water is available for fungal growth.

Generally, bread produced on a commercial scale has relatively low humidity and water activity and is stored at mild temperatures, which hinders the development of most microorganisms. What’s more, companies use additives to increase the shelf life of buns and decrease the chance of developing fungi before the expiration date.

Therefore, these buns tend to deteriorate more easily when handled by consumers, added to inadequate storage conditions (high humidity and temperature) than due to industrial processing conditions.

How to delay the development of moulds on buns?

The best way to delay the development of moulds on buns is to store them in suitable packaging (usually a plastic bag), in addition to requiring them in a dry and well-ventilated place, away from excessive heat and light. 

Most important, when handling the product, you always should have very clean hands, sometimes we are the ones who contaminate our bread.

Is it safe to eat mouldy buns?

No, it is not safe to eat mouldy buns. A bread or bun that has clear visible signs of mould growth should immediately be discarded. This is because consuming mouldy buns can have serious health implications. 

Mould spreads very quickly. When we can see these microorganisms with the naked eye, it means that there is a huge amount of them in the product.

The mould roots are microscopic and can spread quickly through the porous bread. Therefore, it is not advisable to remove the mouldy part and eat the rest.

To read more about consuming mouldy bread, click here


In this brief guide, we are going to answer the question “Is it flour or white mould on buns?”, we are going to look at how to differentiate between both and the potential implications of eating them.

If you have any questions or comments please let us know.


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Hi, I am Charlotte, I love cooking and in my previous life, I was a chef. I bring some of my experience to the recipes on this hub and answer your food questions.