Dairy science logo

    This website

 Site Coordinator | Contributors | Links | Contribute an article or link | News | Forum |


 Cheese starters


 Cheese yield

 Cheese quality

 Cheese science and technology

 Inhibitors in milk

 Cheeses of Piedmont Italy

 Exploitation of anti-microbial  proteins

 Bacteriophages for lactococci

 Primary production

 Ice cream

 Science and technology of wine

 Thermal processing

 Calculators and models

 Harvard reference generator


 Industrial microbiology

 Jobs and careers advice

 Support site

Calculator for converting between Soxhlet Henkel degrees, Thörner degrees, Dornic degrees and percentage lactic acid milk titratable acidity measurements

The acidity of milk can be determined using a pH meter where the hydrogen ion (H+) concentration is measured or more commonly, in industry, by using titratable acidity.

The titratable acidity of milk is the amount of a hydroxyl ion (OH–) solution of a given molar concentration needed to increase the pH of a given volume or mass of milk to a specified endpoint using the titration endpoint indicator, phenolphthalein. This indicator changes colour from colourless to pink. when the pH reaches 8.4. In many textbooks reference is made to the use of normal solutions of NaOH, normality and molarity are identical for NaOH.

Titratable acidity can be expressed in different units depending on the methodology used. The major units are Soxhlet Henkel degrees, Thörner degrees, Dornic degrees and % Lactic acid (Table 1).

Table 1. The major methods used to measure titratable acidity in milk.



Concentration of NaOH used (M)

Countries /areas where used

Typical value for quality raw milk

Soxhlet Henkel degrees,



Central Europe

7 °SH

Thörner degrees



Sweden and Balkans

17 °Th

Dornic degrees



Netherlands and France

15 °D

% Lactic acid

% l.a


UK, USA, Canada, Australia and New Zealand


For further information refer to Bylund (2003).

Product development technologists frequently have to work with different measurement systems for titratable acidity. While Bylund (2003) has provided some helpful information on conversion factors between the different systems the information is limited.

The author has provided a conversion calculator that enables rapid and accurate conversion between all the measurement systems.

Further information

Bylund, G. (2003). Dairy Processing Handbook. 2nd Ed., 440 p. Tetrapak, Sweden.

Fabro, M. A., Milanesio, H. V., Robert, L. M., Speranza, J. L., Murphy, M., Rodríguez, G., and Castañeda, R. (2006). Determination of acidity in whole raw milk: Comparison of results obtained from two different analytical methods. Journal of Dairy Science, 89, 859-861.

How to cite this article

Mullan, W.M.A. (2020) [On-line] Available from: Accessed: