Dried spices can carry salmonella, mould toxins and pesticide residues from open-air drying and long supply chains. Most are treated before sale, but a few precautions still matter at home.
The short answer¶
Spices are agricultural products, often dried on the ground or on mats in the open air, then stored and shipped for months. That makes them prone to picking up bacteria, moulds, insects and dust. Because spices are low in moisture, bacteria do not grow in them, but some can survive for a long time and multiply once the spice is added to a moist food. The risk from spices cooked into a dish is low; the concern is mostly spices added to foods that are not cooked afterwards.
Salmonella and other bacteria¶
Salmonella is the main bacterial concern. The US Food and Drug Administration's risk profile on pathogens and filth in spices, published in draft in 2013, reported that roughly 7% of imported spice shipments it sampled over several years were contaminated with salmonella, about twice the rate for imported foods overall. It also found that around 12% of shipments contained filth such as insect fragments, hair or excreta. Contamination was found in spices from many countries and across many types, including pepper, coriander, cumin, sesame and oregano.
Spices have been linked to a number of outbreaks. One of the most studied was in the US in 2009 and 2010, when salmonella illnesses were traced to black and red pepper used to coat salami. Outbreaks have also been linked to paprika-seasoned crisps in Germany in the 1990s and to sesame products such as tahini.
Spore-forming bacteria such as Bacillus cereus and Clostridium perfringens are also common in dried spices. Their spores survive cooking, and they can grow if a spiced dish, particularly rice or a stew, is kept warm or cooled slowly.
💡 Leftovers
The spore-formers are a good reason to cool spiced rice, dals and curries quickly, refrigerate them within a couple of hours, and reheat until piping hot. The NHS gives the same advice for rice in general.
Mould toxins¶
Moulds that grow on crops in warm, humid conditions can produce toxins that survive drying and cooking.
- Aflatoxins are produced by some Aspergillus moulds and are potent carcinogens. They are a recognised issue in chillies, nutmeg, turmeric, ginger and pepper, as well as nuts.
- Ochratoxin A is another mould toxin found in chillies, paprika and some other spices.
The EU and UK set legal maximum levels for aflatoxins and ochratoxin A in a number of spices, and consignments from some origins are subject to increased checks at the border. Good drying and storage on the farm is the main prevention; there is little a cook can do except buy from reliable sources and throw out anything visibly mouldy or smelling musty.
Treatment before sale¶
Because of these risks, much commercially sold spice is treated to reduce microbes.
| Method | Notes |
|---|---|
| Steam sterilisation | Widely used; short bursts of steam then rapid drying. Can cost some aroma. |
| Irradiation | Permitted for dried herbs and spices in the UK, EU and US; must be labelled "irradiated" in the UK and EU. Little used in European retail. |
| Ethylene oxide fumigation | Used in the US and some producing countries; not authorised in the EU or UK. |
Ethylene oxide made news in 2020 and 2021, when residues were found in sesame seeds from India entering the EU, leading to hundreds of product recalls across Europe, and later in other ingredients such as locust bean gum.
Pesticide residues¶
Surveillance by the EU, the UK and the US regularly finds some spice samples above maximum residue limits for pesticides. These limits are set well below levels thought to cause harm, so an exceedance is a legal and quality problem rather than evidence of danger from a single meal. Importers are responsible for compliance, and repeat offenders face increased checks.
At home¶
- Buy from reputable sellers, whose suppliers are subject to food law, sampling and treatment.
- Keep spices dry, sealed and away from steam. A jar held over a boiling pan draws in moisture, which spoils flavour and can let moulds grow. See storing-spices.
- Take care with raw uses. Spices sprinkled on finished food, dips, dressings and raw doughs are not cooked, so quality matters more there. Toasting (toasting-spices) or blooming in hot oil (blooming-spices-in-oil) reduces microbial load as well as improving flavour.
- Discard anything damp, clumped with mould, webbed or infested. Pantry moths and beetles are a nuisance rather than a poisoning risk, but the spice is spoilt.
- Handle spiced leftovers properly, cooling and refrigerating them promptly.
See also spice-adulteration, lead-in-spices and how-long-spices-last.