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Assessment of two instruments for continuous measurement of the curd-firming of renneted milk

Published online by Cambridge University Press:  01 June 2009

Richard J. Marshall ,
David S. Hatfield  and
Margaret L. Green
Richard J. Marshall
Affiliation:
National Institute for Research in Dairying, Shinfield, Reading R02 9 AT, UK
David S. Hatfield
Affiliation:
National Institute for Research in Dairying, Shinfield, Reading R02 9 AT, UK
Margaret L. Green
Affiliation:
National Institute for Research in Dairying, Shinfield, Reading R02 9 AT, UK
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Summary

Continuous measurements of curd-firming using a commercial vibratingreed viscometer and a pressure transmission system (PTS) developed at this Institute were compared both in the laboratory and during Cheddar cheesemaking. The coefficient of variation about the mean of the curd-firmness measured in reconstituted skim-milk 40 min after renneting was 3·5% with the viscometer and 2·6% with the PTS. The effects of changes in conditions on the curd-firming rate of raw whole milk were determined. As the rennet concentration was raised the rates increased linearly as measured by the viscometer, but non-linearly as measured by the PTS. Addition of CaCl2 increased the rates measured by both instruments rapidly at first then more slowly at higher levels. Raising the temperature increased the rate exponentially in the case of the viscometer but more slowly with the PTS. With both instruments the curd-firming rates of milk at pH 5·8 were 6·5 times those at pH 6·7 but the rates fell slightly at pH 5·6. In experimental cheesemaking, the mean readings of both instruments at the subjectively determined cutting time of the curd had the same coefficient of variation.

The commercial viscometer is probably more suitable for laboratory investigations of the earlier stages of the coagulation of milk by rennet whilst the PTS may prove the more useful in indicating the optimum cutting time of the curd during cheesemaking.

Type
Original Articles
Information
Journal of Dairy Research , Volume 49 , Issue 1 , February 1982 , pp. 127 - 135
Copyright
Copyright © Proprietors of Journal of Dairy Research 1982

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References

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