Determination of solids content of milk by specific gravity lactometer

Abstract

The methods of estimating total solids content of milk having high percentage by Richmond’s formula (TS = 0.25 L + 1.2 F + 0.14) using Quevenne’s specific gravity lactometer, modified Richmond’s formula (TS = 0.25 L + 1.2 F + 0.50) using Zeal specific gravity lactometer, ISI formula (TS = 0.25 DH + 1.22 F + 0.72) and Ling formula (TS = 0.25 DH + 1.21 F + 0.66) using the density hydrometer, along with the percentage of fat estimated by Gerber method were compared with the value obtained by gravimetric method using 307 samples of milk. In all the milk samples analysed the calculated values of total solids by the formula methods were both higher and lower than the gravimetric values.

Since the formulae methods did not give a true estimate of the total solids in milk, modifications to the existing formulae were required by applying a correction factor. It was observed that depending up on the percentage of fat in milk samples, different correction factors were needed to be applied to the different formulae for getting the values close to the gravimetric method. Addition of a correction factor of 0.15 and 0.18 was necessary to the Richmond’s formula for milk samples containing 5.1 to 6.0 and 6.1 to 7.0 per cent fat respectively. For the modified Richmond’s formula, addition of 0.57, 0.53, 0.66 and 0.75 was necessary for samples containing 3.0 to 4.0, 4.1 to 5.0 and 5.1 to 6.0 and 6.1 to 7.0 per cent fat. The addition of a correction factor of 0.16 to the ISI formula was essential for samples containing 4.1 to 5.0 milk fat to get the values in agreement with the gravimetric method. No correction factor was necessary, if Ling formula was used. The order of preference for using various formulae will be (1) Ling formula (2) ISI formula (3) Richmond’s formula (4) modified Richmond’s formula.

Ling formula can be used without any correction factor for determination of total solids content of milk for varying percentages of fat from 3..0 to 9.0.