Manufacture of Condensed Whey and Whey Powder

By far the single largest use of whey solids on global basis is in the form of whole dry whey and it continues to grow. This is whole whey that has been condensed and spray dried as such or after blending with certain other liquid ingredients. These powdered whey products are marketed as commodity ingredients for a variety of foods for human and animals. Since whey is a highly perishable raw material and its use in liquid form is limited to only small quantities, the concentration and drying of whey assumes a special significance. Whey can be preserved as plain or sweetened condensed whey. With the development of membrane technology (reverse osmosis),it became economically feasible to manufacture RO whey concentrates with 28% T.S. retaining all functional properties of whey proteins. The trend in Western Europe is to preserve whey solids in the form of whey powders (demineralised, delactosed whey powders).

i. Concentration of whey

Whey concentration is carried out with the following objectives:

a) Volume reduction for transport to other processing facilities.

b) Pre-concentrate for drying into whey powder.

c) Manufacture of condensed wheys: plain or sweetened.

i) Clarification: The whey always has Curd fines, which confer serious risk of blocking heat exchangers’ channels or fouling Ultrafiltration or RO membranes.These curd fines also adversely affect the solubility properties and flavour of end product. These curd fines are usually removed by a combination of settling,screening and clarification. For large-scale operation, it is usual to employ a self-discharging clarifier with an enlarged solid-holding capacity. Also used commonly are the hydrocyclones where whey is made to flow tangentially into the upper cylindrical part. The centrifugal force causes the particles to move toward the cyclone wall and they get deposited on the bottom.

ii) Separation and Pasteurization: In order to obtain flavour stability in concentrated whey, the whey is separated to remove fat. Then the whey is pasteurized for optimum microbiological quality, to inactivate rennet and storage stability and stored at 5°C till concentration and drying.

iii) Concentration: The whey may be concentrated economically with the integration of Reverse osmosis (RO) for pre-concentration, and multi effect evaporator. The long tube falling film evaporators used for this purpose are characterised by short residence time (5-30 sec.), high heat transfer coefficients and efficient energy use. The most modern concentration installation consists of a 5-7 stage evaporation system. By adding more stages to the evaporator, the specific steam consumption is reduced. A seven-stage plant consumes 50 %  less steam than a three-stage plant. Acid whey foams less during evaporation in evaporators than does sweet whey. When sweet whey is difficult to manage in the evaporator a small quantity of acid or a little fat may be added to break the foam.There is spontaneous lactose crystallisation in vapour separator while concentrating whey to levels above 55% T.S. This may be avoided by immediate removal of concentrated whey from the evaporator apart from controlling final total solids contents of whey and increasing the evaporation temperature of last stage, where lactose is in most concentrated form. For this, the whey evaporators are sequenced in such a way that the higher solids are reached at higher temperature than that prevails in the last stage. For instance a 7-Stage falling film evaporator can be sequenced 1-2-3-4-7-6-5, where the temperature (°C) in the respective stages are 68, 65, 61, 57, 50, 45, and 39.

ii. Plain Condensed Whey

The desirable degree of concentration of plain whey is 35- 50% total solids. Whey condensed to higher solids content (more than 55% T.S.) forms a gel after cooling and is not recommended to be used in any food or feed products due to its coarser texture and low solubility.Plain condensed whey is also made as an intermediate product for whey powder making. The whey is concentrated to about 40-60% solids and pre-crystallized before drying.

iii. Sweetened Condensed Whey

For its preparation sweet cheese whey is mixed with sugar equal to the weight of solids in whey (about 6.7 Kg sugar for 100 Kg whey). The mixture is concentrated using multistage evaporators to at least 76% T.S. The specific gravity of sweetened condensed whey at 50°C is 1.360 (38.4°Be’). The concentrate is always cooled to 30°C using flash coolers and served with lactose crystals. The seeds mixture is stirred for 1 to 3 hr to crystallize the lactose. It may then be packed in barrels or cans. The product does not require any refrigeration for storage.

Sweetened condensed whey darkens and thickens in storage, but these changes do not develop to an objectionable level during first year. The product must be utilized within one year of production to get full advantage of its functional and nutritional properties.Due to high salt content, condensed whey products are somewhat salty and have a characteristic whey flavour. The saltiness may be reduced by desalting the original whey by nanofiltration. A typical composition of different types of condensed whey is given in table

iv. Uses of Condensed Whey

Whey solids in form of condensed whey are used in dairy, bakery goods, baby food, meat products, beverages, soups, sauces, dressings and creams. Concentrated whey has worldwide industrial application in bread and other bakery products. The addition of whey solids in Macaroni and spaghetti improves their viscosity and dough properties. Condensed whey is also used with fruits and jams in various toppings and spreads in confectionery. In addition, whey solids are used in animals feed mixes, as it is a cheap source of high-quality proteins and carbohydrates.

 

Approximate composition of condensed whey’s

 Plain condensed whey and sweetened condensed whey may be used to make various whey candies such as ‘wheyfers’, whipped whey fudge, whey caramel and ‘whey’ taffy. The whipping properties of sweetened condensed whey is of value in many food preparations, say for example ice cream, shakes sherbets and bakery and confectionery products. Uses of whipped sweetened condensed whey include the making of fruit whips, certain candies and frozen dessert preparations. A sweet spread of good keeping quality may be made by mixing equal weights of sweetened condensed whey and peanut. Condensed sweetened whey is also used in caramel production, which is 38% whey solids, 38% sucrose and 24% water.In Norway, “Mysost” and “Primost” cheeses are produced from concentrated whey with 84% total solids. Dulce de leche, yoghurt and whipped cream substitute like milk products contain condensed whey.

v. Lactose crystallization

To avoid the very undesirable caking properties of ordinary whey powder, it is of great industrial importance to get the major part of the lactose content in a crystalline form. The advantage of this lies both in energy savings and in improved powder properties. In the spray drier, it is possible to dry whey concentrate containing up to around 60 % TS, when the lactose content has been subjected to a crystallization degree of 85-90 %. On the other hand, for non-crystallized concentrate, it is not possible to attain more than 42-45 %, TS for drying. Obviously this low degree of concentration has negative effect on the process economics. Controlled crystallization can be initiated by immediate flash cooling of condensed whey after evaporation to about 30°C. As far as possible slow agitation should start immediately; fine grained á-lactose monohydrate at a level of about one Kg. per ton of concentrate should be added. The holding time under these conditions should be 3-4 hours. Cooling of the concentrate should then start, the rate being about 3°C/h until 10°C is reached.

vi. Spray drying

Recent trend in drying of milk and a milk product is extensive use of spray drier that may be single stage, two-stage and more recently three-stage drying. Processes pertaining to the spray drying of whey for the manufacture of various types of whey powder are depicted in Fig.

 

Different processes for the manufacture of whey powder

 i) Single-stage process: In single stage drying product is dried to its final moisture content in the spray-drying chamber alone; some time pneumatic conveying system is adopted with one-stage drying system. Ambient air provides both the conveying and cooling of powder. If climatic conditions prevent powder temperature/residual moisture contents to be achieved with ambient air, the conveying air must be dehumidified and cooled usually to 8°C.

ii) Two-stage process: The principle of two stage drying is a combination of spray drying as the first stage drying and fluid bed drying at the second stage.By two stage drying, it has been possible to obtain good quality powders and also with advantage regarding product quality and drying economy in the manufacture of non-agglomerated products. In this process normally, powders leave the chamber and enter the attached vibrating fluid bed drier with a moisture content of 5-6%. The excess moisture is removed in the fluid bed, where the moist powder is first met by a cold air stream thus avoiding lumping of the thermoplastic powder, and then by a hot air stream for final drying. By introducing cold air in the last stage of the fluid bed the powder is cooled to the desired temperature. Fines are recovered in the spray drier and fluid bed cyclones,collected and returned to the atomizing zone for agglomeration. This agglomeration gives a free flowing powder. In this process typical drying conditions are: feed preheating to 80°C, feed concentration of 50-60%, crystallization, and then drying at inlet temperature of approximately 185°C.

iii) Belt process: Lactic acid in dry form is very themoplastic even at low temperature and diffcult to dry by conventional spray drier. This means tha this type of powder is extremely sticky during the spray drying process, the belt process is especially advantageous in drying lactic acid whey. In the process, typical drying conditions involve preheating to 80°C, feed concentration to 50%, spray drying at inlet temperature of 150°C and outlet temperature of 55°C to a moisture content of 12-15%. In order to avoid condensation in the cyclones, hot air is introduced into the exhaust system of the spray dryer to increase the relative humidity.

The high moisture content of powder leaving the spray drying chamber ensures that crystallization will continue in the powder to an even greater extent than in the two-stage process using fluid bed drier. This crystallization is improved if the wet powder is kept at high moisture content for 10-15 minutes. This is conveniently done on a belt conveyor mounted between the chamber outlet and a fluid bed, where the final drying takes place. The resulting powder consists of large agglomerates, which has a low bulk density, but is extremely instant and have excellent non-caking properties.