Food fermentations can be inoculated either directly with a highly concentrated starter culture obtained from the supplier, or they can be inoculated from a bulk starter propagated locally. The choice between the two process types will be influenced by a number of factors: the number of different fermented products produced in the same factory, degree of automation, presence of expertise in microbiology and, finally, the economics. The highest level of safety and flexibility is achieved by direct inoculation of the culture. In addition to the choice between direct inoculation or bulk starter, there are choices between different culture formulations. The usual options are fresh, dried, or frozen, but their availability differs between suppliers and products.
Baker's yeast is generally inoculated directly into the dough without propagation in the bakery. Yeast is supplied in both fresh and dry forms; fresh yeast can be obtained as liquid, compressed, or crumbled yeast, and dry yeast either as active or instant yeast (8,9,46). Mold cultures are mainly used as direct inoculants, and the common format is a dry spore preparation (2,5,7).
Bacterial cultures are sold as liquid, lyophilized, or frozen cultures. Liquid bacterial cultures will generally lose activity within days, and for direct cultures this format will require a constant supply. Lyophilized or frozen cultures maintain high activity for months or even years, and these formats are ideally suited for global distribution of direct inoculants. Bulk systems for factory propagation of cultures are common for large-scale cheese productions. The cultures used in these systems are supplied from a starter manufacturer in frozen or freeze-dried form, and the media to be used for the propagation is available from the same source (3-10).
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