The effect of preheat treatment and other process parameters on the coffeestability of instant whole milk powder

Agglomerated whole milk powders were manufactured on a pilot-scale milk pow der plant using different preheating conditions as well as adjustment of ot her process parameters. A standard coffee stability test was modified by pr eparing aqueous coffee solutions of varying hardness when testing the exper imentally produced powders. Assaying coffee stability under hard water cond itions differentiated more clearly the effects of different processing para meters, as well as providing more realistic test conditions. Higher evapora tor preheat temperatures (75-120 degreesC) and prolonged holding times (30- 120s) had a negative effect on the coffee stability of whole milk powder, a s did raising concentrate total solids from 43 to 48% in the feed to the dr ier. Concentrate homogenisation and mode of emulsion formation had only a m arginal effect on coffee stability. Optimum concentrate heating temperature was 70 degreesC for the 5 min transmission time the concentrate took to re ach the drier nozzle. Addition of lecithin during the secondary drying stag e improved coffee stability. Coffee sediments contained slightly higher lev els of chi (s)-casein than that of the original whole milk powder. However, the increase in beta -lactoglobulin content of the sediment from 2.1 to 7. 5% as preheat temperature was increased from 75 to 120 degreesC was the mos t notable change that occurred in sediment composition. The results: sugges t that a combination of optimised thermal treatment as well as the attainme nt of the desired powder physico-chemical properties is necessary to achiev e satisfactory stability of whole milk powder in coffee. (C) 2001 Elsevier Science Ltd. All rights reserved.