Experimental milk desserts were composed of reconstituted skimmed milk powder and whey protein isolate as a source of proteins, normal and waxy maize starch, potato starch and hydroxy propyl distarch phosphate (HPDP) as thickeners and ι-carrageenan (ι-C) as gelling agent. The protein and starch concentration varied between 0 and 6%, sugar between 0 and 20% and that of ι-C between 0 and 0.4%. The desserts were heat treated at 100, 110 or 120°C for 10, 20 or 30 minutes. The firmness of the desserts after 24 hours of storage at 20°C, was determined by a cone penetrometric method and expressed as stress in Pa. The logarithm of the stress was a linear function of protein and starch content and of the logarithm of the ι-C concentration (g/100 g). To multiply the firmness of the experimental desserts by a factor of ten, it was necessary to increase the whey protein concentration by 11 to 15 g/100 g depending on the type of starch used. The same effect could be obtained with 5 to 9 g/100 g of starch. When the ι-C concentration increased tenfold the stress level was multiplied by a factor of 2.6 to 4. The desserts’ firmness also depended on the heating time and temperature, even if this effect was small.