„Reduced Dissolved Oxygen Fermentation”: a New Commercial Method
for Rapid, Low Temperature Yoghurt Production, H. Horiuchi, N. Inoue,
N. Orii
By reducing the dissolved oxygen (DO) content of yoghurt mix, we succeeded
in the commercial production of “Bulgarian traditional home-made yoghurt”
which is typically prepared in unglazed pots.
The favorable features of the Bulgarian traditional home-made yoghurt are
related to the following method of production. First, water in the milk is
absorbed into the pot and the milk becomes concentrated. Second, the milk in
the pot is gradually cooled by vaporization and fermentation proceeds at
relatively low temperatures. Thus the yoghurt obtains a thick texture and mild
taste.
We attempted to mimic these conditions. Thick yoghurt mix could be easily
prepared, but as expected the fermentation took much longer time at lower
temperatures, making this procedure unsuitable for commercial yoghurt
production. We recently found that Lactobacillus bulgaricus and Streptococcus
thermophilus remove DO from the yoghurt mix early in the fermentation
process. These lactic acid bacteria begin growing actively when the DO of the
yoghurt mix is reduced to a certain level. We made use of this observation by
reducing the DO content of the yoghurt mix beforehand, by the addition of
nitrogen gas using a static mixer. This resulted in shortened fermentation times.
We call this “Reduced DO Fermentation”, which is currently used in the
production of “Bulgarian traditional home-made yoghurt” in Japan.