Like all raw agricultural goods, products with low humidity levels are exposed to pathogenic microorganisms. Once a product is dried and stored, microorganisms cannot grow but survive in a dry environment, especially pathogens such as Salmonella. Due to their heterogeneous presence, these pathogens are difficult to find and sampling programmes cannot prevent outbreaks. A guaranteed homogeneous treatment is the only way to avoid any risk.
But how can sufficient germ reduction be determined? Based on the evaluation of average pathogen contamination levels, the Almond Board of California prescribes a 100,000 division destruction - a five-log reduction - to make any almond safe for consumption. This figure has become an international standard for the microbiological safety of dry food ingredients and can be validated.
It is difficult to achieve this standard without altering a product's organoleptic qualities. Dry food, in particular, has a tendency to lose taste and texture. Among the most successful solutions is vacuum-saturated steam pasteurisation. With this method, treatment temperatures remain below 100°C and only a minimum amount of humidity is applied. This almost perfectly preserves a product's taste and texture, which is essential for nuts and seeds. It also preserves colour and essential oils, which are very important characteristics of herbs and spices.
At the molecular level, vacuum-saturated steam pasteurisation distinguishes itself from more aggressive treatments, such as roasting. This tends to accelerate the evolution of rancidity in products containing free fatty acids and peroxides, whereas pasteurisation can preserve - and even extend - a food's shelf life.
The combined action of vacuum and steam deactivates the enzyme that transforms fatty acids, leaving treated-pasteurised nuts and seeds free from rancidity for a longer time.