Guzel-Seydim et al.120 followed the production of organic acids and volatiles
during the fermentation of kefir produced in the laboratory from grains obtained
from Turkey. Lactate production started slowly but the concentration of lactate rapidly
climbed to 6000 μg/g by the end of the 22 h fermentation. Citrate, the next most
abundant organic acid, declined during fermentation from 1760 to 1440 μg/g at the
end of the fermentation. Pyruvate levels increased during fermentation to a final
level of 18 μg/g. Levels of orotate and urate declined over the 22 h period; hippurate
was totally consumed after 15 h. Acetic acid, propionic acid, and butyric acid were
not found in any samples. Diacetyl was also absent. Acetaldehyde and acetoin levels
increased as the fermentation progressed. However, ethanol production did not begin
until after 5 h in the fermentation. Guzel-Seydim et al.121 also studied the changes
in organic acids and volatile flavor compounds in kefir stored at 4°C for up to 21 d.
Lactate was the organic acid in highest concentration (> 6000 μg/g), followed by