An electrical resistance method, which has the potential to measure the extent of soft material fouling such as milk fouling on the surface of process equipment in situ and in real time, is described. An experimental fouling unit with the appropriate attachments has been devised and used to monitor the fouling build-up using the electrical resistance method. Reconstituted skim milks with solid contents of 10-30 wt.% were used to produce milk foulings, and these milk foulings were cleaned using a cleaning solution with 0.5 wt.% NaOH. Using the fouling unit, it was possible to measure the thermal resistance (essentially measuring heat flux) and electrical resistance simultaneously. As a result, the relationship between the electrical resistance and the thermal resistance during both fouling build-ups and cleaning processes was established. It has been shown that this technique is effective for measuring the extent of fouling, and it has the potential to be modified further so that it can be adopted in real process industries. (C) 2003 Elsevier Ltd. All rights reserved.