The present invention relates generally to a shirred concertina formed from a seamless, tubular foodstuff casing that is tied-off at one end, and has an outer surface provided with a coating or impregnation including a food additive. The tied-off end of the present casing is turned back inwardly, into the hollow cavity formed by the concertina. Concertinas of the present invention are particularly adapted for use with automatic sausage filling, portioning, and clipping machines.