Measurement of the colour of clear and hazy juices (Spectrophotometric method)
Principle. The colour of a juice is an important quality criterion. In some juices a relatively light colour is expected for a good quality, such as apple or grape juices. However, in red/black juices a deep red/purple colour is expected in good quality juices. The colour of a juice can be determined spectrophotometrically by measurement of its absorbance or transmission in the visible region of the spectrum. In yellow/brown products e.g. apple, pear, white grape juices the absorbance is measured at 430 nm. In red/black juices e.g. blackcurrant, raspberry etc. the absorbance is measured at 520 nm.
The text has been slightly revised to clarify part of the procedure.
The revised method can be access via the methods section of the IFU website www.ifu-fruitjuice.com