Steam sterilisation exposes dried herbs or spices to saturated steam under controlled pressure for a short, precisely defined period, then removes the added moisture by immediate re-drying. It reduces the microbial load, including spore formers, and carries no labelling obligation. It is the mainstream decontamination route in the European market.
Why it works this way
Dried herbs and spices are field crops. Total plate counts in the millions per gram are normal on untreated leaf, and spore-forming organisms survive drying. Where the spice enters a product with a downstream cook step, that load is a specification question. Where it enters a ready-to-eat product – a seasoning on a finished snack, a dry rub, a supplement – it is a safety question.
Saturated steam works because condensing steam transfers heat to the product surface rapidly, so the lethal effect is delivered in seconds to minutes rather than in the minutes to hours a dry heat process would need. Short exposure limits the damage to volatile oil and colour, though the damage is still greater than under irradiation at an equivalent reduction.
The re-drying step is where the process goes wrong. Steam adds water, and a lot that leaves the steriliser correctly treated but arrives above the moisture specification has had a bad re-dry. The consequence is a water activity problem, not a microbiological one.
What follows in practice
Require moisture and water activity on the post-treatment certificate, and require the volatile oil figure to be measured after treatment rather than on the untreated material. Ask for before and after data on the same lot; a plant running a controlled process will have it.
Irradiated against non-irradiated spices works through when a treatment is needed at all.