Does rice mould? (+3 ways to spot bad rice)

In this article, we are going to answer the question “Does rice mould?” and discuss how to know if rice is moulded, the shelf life of rice, and how to store rice to prevent mould growth.

Does rice mould?

Yes, both uncooked and cooked rice are susceptible to developing mould (1, 2). Uncooked rice can be contaminated by mould during harvest or processing and storage. Bad storage conditions, especially in humid environments can lead to fungal development.

Cooked rice can allow the growth of mould when it is improperly stored or stored for a prolonged time. Uncooked rice can contain moulds which resist cooking.

Although the amount of viable fungi is reduced after cooking, they can be still high and represent a health risk, as they can produce toxins during storage.

How to know if rice contains mould?

To know if rice contains mould, you should look for signs of grain damage, development of mycelia or hyphae and discolouration of the grains. Fungi invade the grains and cause both grain physical damage and colour changes (1).

Another indication of mould growth is the change in the odour of the grains. Uncooked rice is generally neutral in the odour. However, many volatile compounds, such as alcohols, alkanes and aromatic compounds are produced by moulds, which characterize the off-odours perceivable when rice is infested by fungi (3).

In the case of cooked rice, changes in the texture, colour and odour are possible indications. However, in general, spoilage caused by fungal growth does not occur in an isolated form, but rather together with spoilage caused by other microorganisms, including yeasts and bacteria (2).

What is the shelf life of rice?

The shelf life of uncooked rice can vary between some months to several years, depending on many factors, such as the type of rice and the storage conditions (4, 5).

Typically, brown rice has a shelf life of one year when kept unclosed and stored in a cool and dark place (6), and 4 years when protected from moisture and oxygen and stored at refrigerated or frozen temperatures (5).

White rice can be stored for several years at refrigerated temperatures when kept in plastic containers free from oxygen (4).

Cooked rice has a shelf life of 4 to 6 days in the refrigerator or about 6 months in the freezer (6).

How to store rice to prevent mould?

To correctly store uncooked rice and prevent mould contamination, it is necessary to protect the grains from moisture, oxygen and from possible invasion of insects and fungi.

Good hygienic conditions during harvest, transportation and commercialization are necessary, as well as good storage conditions (1, 2). Packaging with a good oxygen and moisture barrier, such as PETE and glass containers is effective in prolonging the shelf life of uncooked rice (4).

Storing uncooked at low temperatures can improve the shelf life of both white and brown rice for several years, as it reduces the oxidation reactions, which cause rancidity in brown rice, especially (5).

Cooked rice should be stored in the refrigerator or freezer and should be consumed within its shelf life (6). Long storage time or improper storage, such as keeping cooked rice unrefrigerated, can lead to the fast growth of pathogenic microorganisms, compromising the quality and the safety of the food (2).

Other FAQs about Rice which you may be interested in.

How long does rice flour last?

Does sticky rice have gluten?

Does rice double when cooked?

How long can you eat rice after cooking?

What is the risk of eating moulded rice?

The risk of eating moulded rice is of having a foodborne illness due to possible infections caused by moulds themselves and of poisoning caused by the ingestion of fungal toxins.

Fungi produce toxins that can cause negative effects on health, especially when ingested throughout a lifetime (1, 2). Toxins produced by Aspergillus, Penicillium, Rhizopus and other fungi commonly found in rice are mutagenic, hepatotoxic, nephrotoxic and carcinogenic.

Conclusion

In this article, we answered the question “Does rice mould” and discussed how to know if the rice has moulded, what is the shelf life of cooked and uncooked rice, how to properly store cooked and uncooked rice to prevent mould, and what is the risk of eating moulded rice.

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References

1.-

Reddy KR, Reddy CS, Abbas HK, Abel CA, Muralidharan K. Mycotoxigenic fungi, mycotoxins, and management of rice grains. Toxin reviews. 2008 Jan 1;27(3-4):287-317.

2.-

Tahir A, Hameed I, Aftab M, Mateen B. Microbial assessment of uncooked and cooked rice samples available in local markets of Lahore. Pakistan Journal of Botany. 2012 Mar 1;44(3):67-270.

3.-

Magan N, Sanchis V, Aldred D. The role of spoilage fungi in seed deterioration. Mycology series. 2004;21:311-24.

4.-

Utah State University. Storing white rice [Internet]. Usu.edu. [cited 2023 Aug 21]. Available from: https://extension.usu.edu/preserve-the-harvest/research/storing-white-rice

5.-

Kawamura S, Takekura K, Yokoe M. Freezing Temperature and Freezing Injury of Rough Rice, and Quality of Rough Rice Stored at Temperatures between–50° C and 25° C for Four Years. In2005 ASAE Annual Meeting 2005 (p. 1). American Society of Agricultural and Biological Engineers.

6.-

Usda.gov. [cited 2023 Aug 15]. Available from: https://www.fsis.usda.gov/shared/data/EN/FoodKeeper-Data.xls