The addition of fat to the whey concentrate prior to the drying is used. 26 to 50% of the dry matter is normal. This product is then used directly or in a dry-mixing operation to make different calf milk replacers. The fat used is mainly of a cheap sort such as lard or tallow. Precautions against the presence of polyunsaturated fat acids should be taken by addition of antioxidants to prevent fires in the dryer.
Wall deposits can be avoided to a great extent by introducing warm air at 60ºC tangentially into the drying chamber at the cylindrical part of the chamber. The amount of air to be used is about 5-10% of the amount of drying air.
40% fat-enriched whey powders have proved to dominate the market. The most suitable plant for this product is the Compact dryer, discussed on page 143, and below are the recommended technological processing steps:
1. Sweet whey of good quality with normal content of whey proteins should be used, i.e. casein whey is not recommended, as the whey protein content is low resulting in high free fat levels and fat emulsion stability. The pH should not be lower than 6.3-6.4 in the raw whey. It is possible to neutralize with Mg(OH)2 to improve the fat emulsion stability, and to stabilize especially salts of citrates, phosphates and lactates. The whey proteins should not be hydrolysed and a good indication is max. 150 NH4+/100 g solids.
The lower pH in the raw whey, the more neutralizing agent, and the more diffi-cult the drying. Powder of inferior quality is the end result.
2. Immediately after the cheese process the whey must be pasteurized at 72ºC for 15 sec. and cooled to 4-5ºC for storage.
3. Pasteurization to 80ºC, no holding, before evaporation to 50% solids and flash-cooling to 30 C.
4. Cooling to 25ºC during 5 hours (1ºC/h) in crystallization tanks.
5. Addition of sodium hexametaphosphate or sodium polyphosphate to bind Ca++ ions.
6. Mixing fat and 1-3% emulsifiers at 60-70ºC.
7. Mixing fat/emulsifier with the whey concentrate.
8. In-line heating by means of a concentrate pre-heat exchanger to 65ºC. The hold-ing time of the concentrate at this temperature should be as short as possible to avoid melting of the lactose crystals.
9. Two-stage homogenizing at 80/50 bar g.
10. Spray drying, preferably with CIP-able bag filter to avoid problems with blocked cyclones.
11. During spray drying addition of free-flowing agent.
12. Cooling in a Vibro-Fluidizer and bagging-off.
See Fig. 137.
Fig. 137 Processing of fat-enriched whey powder
For 50% fat in whey the Multi-Stage Dryer with CIP-able bag filter is recommended (see page 203) due to its special design, where the concentrate is sprayed onto the fluidized powder layer to avoid excessive powder deposits in the plant. For higher fat contents the product becomes too difficult to dry due to severe powder deposits in traditional spray dryers. The integrated belt dryer, type FILTERMAT® (FMD), see Fig. 138, is therefore chosen. In this plant the concentrate is sprayed downwards onto a slowly moving belt on which the powder accumulates as a layer (mat) of powder, which is continuously being conveyed out of the drying zone into the after-drying and cooling zone. The process air (primary drying, secondary drying, and cooling) is ex-hausted through the powder mat and the belt (consisting of a porous synthetic food-grade material) and through a cyclone. The amount of powder entrained in the air from the drying chamber is very low. The cyclone is, therefore, equipped with a bucket for manual emptying of the fines powder.
Fig. 138 Integrated belt dryer type FILTERMAT® (FMD)
The use of whey powder with or without fat is extensive. However, the biggest part is used as animal fodder either direct (up to 50% of the total food) or as an ingredient in a final-formulated mix.