PROCESS AND APPARATUS FOR THE CONCENTRATION OF ACID WHEY

Abstract: Process and apparatus for the concentration of acid whey to a dry solids content above 45% by weight under reduced pressure in at least two separate phases. Between at least two of these phases partially concentrated whey is stored for an adjustable average residence time of at least30 minutes at a temperature above 35`C, most preferably of 40 to 60`C.

Description: 570 Process and Apparatus for the concentration of acid whey. The invention relates to a process and an apparatus for the con- 4 centration of acid whey to a dry solids content of more than 45 % by weight. Whey is the product, which is obtained after precipitation and separation of casein containing milk proteins from milk. When the precipitation is effected by the action of ensyms, the produkt after the separation of the casein is called sweet whey. When the milk is acidified by fermentation or acid is added to the milk, the product obtained after separation of casein is called acid whey. In the latter case the uπdissolved calcium salts present in the αilk are dissolved due to the reduction of the pH, so that acid whey contains considerably more dissolved salts than sweet whey. When processing whey, which in most cases contains about 6 % by weight of dry solids, to form whey concentrate or whey powder and in the preparation of lactose from whey a considerable amount: of water must be removed from the whey. Initially the water was evaporated from the whey with one stage evaporators according to the recycle principle, lateron multistage evaporators were used (M.T.Gillies, "Whey Processing and Utilization", Noyes Data Corporation, Park Ridge, N.J. and London (1974), pages 24-29). 3efore the evaporation the whey may be maintained some time at a temperature of 65-74 β C in order to prevent bacterial growth and development of acid and there¬ after be preheated at 87 - 96"C and, if desired, be pasteurized. Thereby the whey proteins are denatured and the lactose is brought to crystallization. The whey is concentrated to a dry matter content of 40 - 50 7. by weight and thereafter dried with a spray dryer. Evaporation of whey with the use of an number of vacuum evapor¬ ators in series to a dry solids content upto 70 % by weight is known from John R.Spellacy, "Casein, dried and condensed whey", Lithotype Process Co., San Francisco (1953), ~~Ό . 489, 490,491, 500 and 501. From Earl O.Whittier and 3yron H.Webb, "3y-products from Milk", Reinhold Publishing Corporation, New York, (1950), pp. 298, 299 and 305-307 a process is known, in which casein whey is heated with steam to boiling with the addition of a small amount of milk of lime, whereby the whey proteins coagulate and form together with calcium OMPI " 7 2 phosphate a sludge at the bottom of the tank. The separated clear whey is thereafter concentrated under reduced pressure in two or three steps to a dry solids content of 34 ^ - 38 7, by weight. The syrup obtained is filtered in a filter press to remove the separated proteins and salts. By the denaturatiαn of pro¬ teins the viscosity rises namely, which causes difficulties during the further concentration. The filtered syrup, which thereafter does not contain whey protein, but only lactose, is further concentrated to a dry solids content of about 70 7. by weight. From Dairy Science Abstracts 1977, vol.39, nr. 4, p.212, abstract 1355 it is known to concentrate whey to a dry solids content of more than 45 Z by weight, to cool subsequently the concentrated whey to 27-30°C and to maintain it at this temperature under agitation for 8 - 12 hours, whereby the lactose present ia the whey crystallizes. The whey with the crystallized lactose is then heated and spray-dried. To speed up the concentrating of the whey at less higher tempe¬ rature, whereby the denaturation of the whey proteins causes less trouble, now also falling-film evaporators are used. Thus, in Dairy Science Abstracts, vol.39, nr. 4 (1977), p.212, abstract 1854 a process has been described, wherein whey having a dry solids content of 6 7, by weight is concentrated in an equipment consisting of several falling-film evaporators to a dry solids content of 36 % by weight. According to the German "Offenlegungsschrift" 2,538,336 milk and milk products are evaporated in an equipment consisting of a t_t_~- ber of evaporators. In at least one evaporator the material to be concentrated is evaporated in a rising stream, whereafter in one or more following evaporators the operation is carried out according to the falling film principle. Whey, which has been evaporated in this way, will contain only little or no denatured protein. When, however, the heating surface of the evaporator(s) becomes fouled and the temperature must be raised to continue the evaporation, nevertheless denaturation takes place, whereby the rate of fouling increases more. Such a fouling of the surfaces of an evaporating apparatus especially takes place when concentrating acid whey. Such as is known from the Netherlands Patent Specification 132,095 calcium salts of _O P & 3 phosphoric acid and citric acid present in the whey are present in a well soluble form at pH values below 4,7 it is true, the acid radicals being dissociated only one time, but it has appeared in practice that nevertheless calcium containing precipitates are formed on the surface of an evaporating apparatus. This holds especially for acid whey obtained after precipitation of casein with sulphuric acid, but also other types of casein whey as well as cheese whey originating from a cheese preparation process, in which the formation of lactic acid plays a part, show a much stronger fouling during concentration than sweet whey. In addition to calcium in the deposits upon the evaporator sur¬ face phosphate, sulphate and organic compounds, like sugar type and protein type substances,can be found. These deposits occur especially at those places, were the dry solids content in the whey is high. Already after some hours of evaporation the heat transfer of the evaporator surfaces decreases and after 5 to 6 hours of evaporation the evaporation must be interrupted due to excessive fouling. In order to avoid these disadvantages it has been proposed ac¬ cording to the Netherlands Patent Application 7.310.035 to remove calcium from the whey to be processed with the aid of an acid ion ex¬ changer in the sodium or potassium form and to regenerate the ion ex¬ changer used with the aid of a liquid obtained at a later stage of the whey processing. It has been found that the fouling of the evaporating equipment when concentrating acid whey to a dry solids content above 45 % by weight by evaporation under reduced pressure with the aid of continuous evaporators is reduced considerably without treatment with ion exchanger, when according to the invention the concentration is carried out in at least two separate phases and between at least two of these phases the already partially concentrated whey is stored in a storage zone for an adjustable average residence time of at least 30 minutes at a temperature above 35 β C. Each separate phase of the concentration can be carried out in one of more evaporation steps. This can occur in several ways. Thus, an evaporating equipment may be used consisting of a series of evaporator units connected with each other in such a way that the vapour obtained in a evaporator unit serves as heating agent OMPI * 4 for the next evaporating unit, each evaporating unit is provided with a cooling device for the separated product from which the concentrat¬ ed liquid phase is withdrawn to a next evaporator unit and the vapour is used for the heating of a preceding evaporator unit. Thus theore - ically in such a process only to the last evaporator unit a heating agent, such as steam, need to be added, the heat content of which is then always transferred to a preceding evaporator unit through the vapour. As evaporator unit several types of evaporators can be used, such as circulation evaporators and preferably falling-film evapor¬ ators- In the process of the invention partially concentrated whey coming from one of the evaporator units is withdrawn and stored in a separate zone, e.g. in a so called buffer tank. After a storage of at least 30 minutes the partially concentrated whey is fed into a next evaporator body. In the process of the invention also multi-stage evaporators can be used consisting of several evaporation stages each provided with a cooler with vapour separator and withdrawal conduits for vapour and liquid. According to the invention the- partially concan- trated whey obtained from a stage can be withdrawn from such a vapour separator belonging to a evaporation stage and stored for at least 30 minutes in the storage zone and thereafter fed again to a next " ' ' evaporation stage. For heating the evaporating equipment in most cases steam is used, although also other heating agents can be used. In general the heating takes place in a indirect way. The temperature in the evaporators is determined by the equip¬ ment available and the purpose aimed at. 3ecause denaturation of the proteins in the whey must be avoided as much as possible, the tamper- ature is generally not higher than S0°C, preferably 40 to 70 3 C and especially 40 to 60 β C. 5 The pressure in the evaporators is dependent on the temperature and the desired degree of concentration. The conditions of temper¬ ature and pressure in general do not deviate from the conventional conditions. The temperature in the storage zone is usually determined by the temperature of the evaporator units or evaporating stages and is therefore preferably 40 to 70°C and especially 40 to 60 β C. It is de¬ sired to maintain the temperature in the storage zone as much con¬ stant as possible and, of course, preferably as much as possible heat loss is prevented during the storage period. Fouling is most pronounced in the evaporator units or evaporat¬ ing stages, in which the dry solids content is the greatest. For that reason it is preferred, especially when the whey should be con¬ centrated to a dry solids content of more than 60 % by weight, to store the whey in a storage zone, when the dry solids content is 45 to 55 Z by weight. Because, however, also in the evaporator units or evaporating stages, in which the content of this substance is not so great, a rather substantial fouling occurs,- in addition thereto the storage of whey having a dry solids content of 30 to 45% by weight in a storage zone is desired. If the whey is not further concentrated than to a dry solids content of 45 to 50% by weight, it is sufficient to store whey having a dry solids content of 30 to 45% by weight in a storage zone. When strongly concentrating the whey one proceeds for example in such a way that the concentration is carried out in three phases, after the first phase whey having a dry solids content of 30 to 45% by weight is stored in a storage zone for an adjustable aver¬ age residence time of at least 30 minutes at a temperature in the range of 40 to 60"C, subsequently the whey is further concentrated in a second phase, thereafter the whey having a dry solids content of 45 to 55% by weight is stored in a storage zone for an adjustable aver¬ age residence time of at least 30 minutes at a temperature in the range of 40 to 60 β C and finally in the third phase whey is concen¬ trated to a dry solids content of 55 to 70% by weigh . 6 The average residence time of the partially concentrated whey in the storage zone must be adjustable, so that it is prevented that the whey is flowing to the next evaporating step or the next evaporator unit respectively directly through the storage zone. In practice an average residence time of 1 to 5 hours is desired, dependent on the equipment used and the dry solids content of the partially concen¬ trated whey. By carrying out the concentration of thβ whey in at least two separate phases and the insertion of an storage period of the part- ially concentrated whey between two evaporating phases it is achieved that the fouling of the evaporator surfaces when processing whey having a rather great dry solids content is reduced considerably, while nevertheless thβ total effect of thβ evaporating equipment need not to be disturbed, because the dry solids content in the partially concentrated whey and the temperature thereof need not undergo a change. The fouling in an evaporator unit is measured with reference to the heat transfer. When no fouling occurs, the heat transfer remains- constant and also the water evaporating capacity remains constant without the need of further adjustment of the temperature or the throughput. Thereby thβ temperature throughout the evaporating appar¬ atus can be maintained at such a low value, that denaturation of pro¬ teins does not occur. Thereby thβ whey concentrate contains the whey protein finally substantially completely in a non-denaturated state. This means that thβ whey concentrate has a high content of soluble protein. In thβ preparation of lactose from the whey concentrate the separation between crystallized lactose and the other whey ingre¬ dients can take place better. The resulting whey concentrate can be dried in the conventional way to whey powder, e.g. by means of spray-drying, and/or be proces¬ sed to lactose. The invention also relates to a apparatus for carrying out the above described process, consisting of an apparatus for the evapor¬ ation in at least two zones, in which the first zone is provided with an inlet for starting material and each zone is provided with a cool¬ ing device for the product withdrawn from said zone and a vapour separator as well as with the conventional means for the transport of 7 liquid and vapour and for measuring and controlling the temperature, pressure and liquid- or vapour rate and other conditions. The ap¬ paratus according to the invention is characterized in that between at least two different evaporating zones a storage zone is present, provided with an inlet for liquid originating from the preceding evaporating zone, with an outlet to the next evaporating zone and with means for storing liquid for an adjustable average residence time at a predetermined temperature Preferably the storage zone is a vessel with means for control- ling temperature and residence time. Thβ following examples explain the invention. Therein the foul¬ ing is determined with reference to the heat transfer coefficient, the so called K-value. This K-value is calculated from the formula: Q.V X - ΔT.O in which Q represents the amount of separated condensate in kg/h per body, ΔT represents the temperature difference in β C, 0 thβ -size of the heating surface in *~r and V the evaporation heat of water in kJ/kg. Example I. Acid whey having a dry solids content of 6.0 % by weight , ob¬ tained after acidification of skim milk with hydrochloric acid to a pH of 4.5 and separation of the casein precipitated thereby, was con- centrated to a final dry solids content of 60 % by weight with an evaporating equipment comprising totally 7 evaporator units according to the falling-film principle in series. The whey concentrate from the fifth evaporator unit having a dry solids content of 48 % by weight and a temperature of 50° C, was passed through a tank, before it was pumped into the sixth evaporator unit . The residence time of the partially concentrated whey in this tank was on the average 1 hour. After 4% hours of evaporation the K-value of the sixth and seventh evaporator unit appeared to be reduced with 14% . When the average residence time in the tank was 5 hours , the K-value in the last two evaporator units appeared to be reduced with 10% after 4% hours of evaporation, with a residence time of on the aver¬ age 3 hours no reduction of the -valua was found after 8 hours . _. OMP V# IP 70 3 If on the contrary thβ whey concentrate from the fifth evapor¬ ator unit was passed immediately, therefore without storage in a storage zone, to the sixth evaporator unit, the K-value of the last two units appeared to be reduced with 36 after 4% hours of evapora- tion. Ξxamo * le II. Acid whey having a dry solids content of 5 , 9Z by weight, obtain¬ ed by acidification of skim milk with sulphuric acid to a pa of 4.5 and separation of the casein precipitated thereby, was concentrated to a dry solids content of 60S by weight of the final product with the same equipment as used according to example I. The shey concen¬ trate coming from the fifth evaporator unit had a dry solids content of W1Z by weight and a temperature of 52 β C. With a residence time of this concentrate of on the average 1 hour in a storage tank the value of the K-value of thβ next evaporator unit appeared to be reduced with 12% after 4.6 hours of evaporation. Wi h a residence time of on thβ average 6 hours the K-value appeared to remain constant for 7.5 hours of evaporation. Example III. The same whey as described in example II was treated with a si¬ milar equipment as described in example II, but now the concentrate from the fourth evaporator unit having a dry solids content of 38« by weight and a temperature of 52 β C was stored for on the average 5.5 hours in a tank before being passed to the fifth evaporator unit. As appeared from the fact that thβ K-value of the fifth evaporator unit remained constant, in that unit no fouling occurred for 5 hours of evaporation. Without thβ storage of the partially concentrated whey th β K-value of the fifth evaportor unit appeared to decrease with 30S in 5 hours.

Claims: 9 C L A I M S . 1. Process for the concentration of acid whey to a dry solids content above 45% by weight by evaporation under reduced pressure with the aid of continuous evaporators, characterized in that the concentration is carried out in at least two separate phases and between at least two of these phases the already partially concen¬ trated whey is stored in a storage zone for an adjustable average re¬ sidence time of at least 30 minutes at a temperature above 35°C 2. Process according to claim 1, characterized in that the several phases of the concentration are carried out with the aid of different evaporator units. 3. Process according to claim 1, characterized in that the al¬ ready partially concentrated whey is withdrawn after a stage in a multistage evaporator and is fed after the storage to the subsequent stage in the same multistage evaporator. 4. Process according to the claims 1-3, characterized in that thβ whey is stored at a temperature in the range of 40 to 70°C and preferably 40 to 60"C 5. Process according to the claims 1-4, characterized in that the whey when stojςe has a dry solids content of 30 to 45% by weight. 6- Process according to the claims 1-4, characterized in that the whey when stored has a dry solids content of 45 to 55% by weight. 7. Process according to one or more of the preceding claims, characterized in that the concentration is carried out in three phases, after the first phase whey having a dry solids content of 30 to 45% by weight is stored in a storage zone for an adjustable average residence time of at least 30 minutes at a tamperarature in the range of 40 to 60°C, subsequently the whey is further concen¬ trated in a second phase, thereafter the whey having a dry solids content of 45 to 55% by weight is stored in a storage zone for an ad¬ justable average residence time of at least 30 minutes at a temperat¬ ure in the range of 40 to 60°C and finally the whey is concentrated in the third phase to a dry solids content of 55 to 70% by weight. 8. Process according to one or more of the preceding claims, characterized in that the whey concentrate obtained is dried to whey . 10 powder and/or processed to lactose. 9. Apparatus for carrying out the process according to one or more of the preceding claims, consisting of an apparatus for the evaporation in at least two zones, in which the first zone is provid- ed with an inlet for starting material and each zone is provided with a cooling device for the product withdrawn from said zone and a vapour separator as well as with the conventional means for the transport of liquid and vapour and for measuring and controlling the temperature, pressure and liquid or vapour rate and other conditions, characterized in that between at least two evaporator zones a storage zone is present, provided with an inlet for liquid originating from thβ preceding evaporation zone, with an outlet to the next evaporation zone and with means for storing the liquid for an adjust¬ able average residence time at a predetermined temperature. 10. Apparatus according to claim 9, characterized in that the storage zone is a vessel with means for controlling temperature and residence time.

Inventors: TERMOTE F
Applicants: DMV CAMPINA BV, TERMOTE F
Application year: 1981
Main classification: A23C21
IPC codes: A23C1