a false-bottomed vat. The acetifying stock is sprayed on to the surface of
the packing material and trickles down against a counter-current of air
which is either pumped through the bed or drawn up by the heat of
reaction within it. The packing material normally consists of some
lignocellulosic material such as birch twigs, vine twigs, rattan, wood
wool, or sugarcane bagasse, although other materials such as coke have
also been used. The vinegar stock is collected in a sump at the bottom of
the vat and recirculated until the desired level of acidity is reached. The
faster rate of reaction achieved means that the wash heats up during
passage through the bed and, depending on the size of the fermenter,
some cooling may be required.
The process is operated semicontinuously to maintain a high level of
acidity throughout, and most of the biomass is retained within the
packed bed. A well operated quick vinegar process fitted with temper-
ature control and forced aeration can usually acetify a vinegar stock with
a GK of 10 and an initial ethanol content of 3% in 4–5 days.
The fastest rates of acetification are achieved using submerged acet-
ification in which acetic acid bacteria grow suspended in a medium which
is oxygenated by sparging with air. The most commercially successful
technique to have been developed is the Frings Acetator (Figure 9.16)
which uses a patented self-priming aerator to achieve very efficient
oxygen transfer.
Figure 9.15 The Orleans process of vinegar manufacture
Chapter 9 359