While it’s true that herbs and spices make up only a minor component of our diets, some people are concerned about pesticide residues on the plants that yield these flavor agents. But the use of chemicals on herbs and spices is not restricted to the growing cycle. Insect or microbial contamination can occur post-harvest, during transportation, storage and processing. Because most of these plants are grown outdoors, they tend to have high microorganism counts to begin with. Given all of this, herbs and spices must be sterilized to prevent foodborne illnesses and reproduction of the microbes or bugs. There are several ways in which sterilization can be accomplished.
Conventional herbs and spices are sometimes sterilized with the gas ethylene oxide (EtO). But EtO is problematic. It is highly combustible and has been identified as a carcinogen and reproductive toxin; some claim it can also damage the typical sensory characteristics of herbs or spices. EtO, incidentally, has been banned in many European countries, as well as in Japan.
Irradiation is another technique that is sometimes used to sterilize spices, although this method has also been banned in some countries outside the U.S. The Centers for Disease Control and Prevention (CDC) describes irradiation as “a safe and effective technology that can prevent many foodborne diseases.” The CDC further states that irradiated foods do not experience a change in nutritional value and are not made unsafe by their exposure to irradiation.
However, not everyone accepts these reassurances. And, according to one article I’ve read, a high dose of radiation is required to kill insects and bacteria and extend the shelf-life of an herb or spice. Irradiated spices, unlike many other irradiated foods, do not require a label stating they’ve been radiation-treated. Not all sellers of conventional herbs and spices sell irradiated spices, by the way; some refuse to do so.
Organic spices and herbs are not allowed to be radiation-treated, nor can they use EtO. Instead, these products use heat, steam, ozone, carbon dioxide or a freezing process. No one method works for all herbs and spices, unfortunately. Heat sterilization kills bacteria, but it can damage the essential oils and flavor of herbs. Carbon dioxide chambers can kill insects and their eggs, but can’t sterilize. Freezing will not kill all microorganisms, especially in products that typically have high microbial counts, such as garlic. There is even a process by which soil is treated before plants are even grown in it, so bacteria is limited from the start, but on a large scale this doesn’t seem practical.
In 2006, BI Nutraceuticals of California came up with a steam sterilization process for herbal powders, called Protexx HP™, a sanitation technology based on super-heated dry steam. According to the BI Nutraceuticals website, results of treatment with this technology are similar to reduction in microbiological counts seen with either irradiation or EtO sterilization; but Protexx HP protects color, flavor, and other sensory properties, leaves no residue, is environmentally friendly, and has been certified organic. The company tells me that their technology is now being used for sterilization on a number of organic products, including some herbs and spices.