Fermentation in sodium chloride (NaCI) brine by naturally occurring micro-organisms is an established procedure for temporary preservation of cucumbers in open-top tanks. The physical attributes and accessory supporting equipment of an anaerobic, closed-top tanking system with the potential to reduce environmental problems and facilitate the use of new fermentation technology is reviewed and updated. Prototype tanks of 30 to 35 m 3 capacity and fibreglass construction having a food-grade liner were selected for introductory stage testing and semi-commercial evaluation. Anaerobic conditions were achieved by sealing the manhole port located at the tank top and purging the brine with nitrogen (N,) gas to remove oxygen.
The purging (at rates up to 1.0 m~/h) served to remove carbon dioxide (CO2) generated during fermentation and also operated as a gas lift pump to circulate the cover brine. During fermentation, N: and CO2 gases were vented from the tank top through a 50 mm diameter vent tube at atmospheric pressure. During storage, anaerobic conditions were maintained by a slight (approximately 250 mm water column) positive pressure of N~ in the headspace above the liquid level; a U-tube manometer served as a means of isolation, a pressure indicator and a safety device against excessive positive or negative tank pressures. Field trials to the system under commercial conditions have demonstrated that anaerobic tanks can alleviate many of the objectional features of open-top tanks. Implications of projected modifications of the system are briefly examined.