This paper presents the results of the theoretical and experimental studies of newly designed devices, namely, the VRSh-1 ball rheometer and the Sgustok-1S dual-range rotary viscometer, for the continuous automatic monitoring of structure formation processes in milk–protein blobs. Each type of rheometers is studied to substantiate and select their geometric and kinematic parameters and the shape of measuring elements. It has been shown that the mechanical actions on the structure of milk–protein blobs during the rheometric monitoring of their formation must be minimal to obtain reliable data on their readiness. It has been proven that the monitoring of the formation of blobs by the method of the low-amplitude dynamic oscillations of a ball does not necessitate the measurement of the phase shift of its oscillations, and the total force of the resistance of a strengthening clot to the displacements of a ball inside it should be selected as a control parameter, which is in direct proportion to the amplitude of linear displacements of a ball in a viscoelastic medium (blob). Such a solution simplifies the design of a rheometer and makes it possible to obtain a similar rheogram, which precisely and reliably describes the coagulation of a milk mixture. The possibility of switching the rigidity ranges of force indicators without stopping the electrical drive, the design of which prevents a formed blob from dynamic impacts, thus providing the precision of monitoring and the preservation of the structure of a blob, has been designed for the method a cylinder rotating in a formed blob. The algorithm of the computer approximation of rheometric monitoring results for the formation of milk–protein blobs with the possibility of correcting its consistence at the terminal stage of coagulation is described.
milk blobs, process rheometers, monitoring, quality, image identification, approximation
Milk and dairy products hold a specific place among the most popular foods, which help a human organism to adapt to deteriorating environmental conditions . The principal stage of the production of any cultured dairy product is the coagulation of proteins and the formation of a blob of desired consistency, the main characteristic of which is the strength and mechanostructural properties . The readiness of a milk–protein blob in the production of cheeses was estimated visually at most enterprises until now . The reliability of the results of such a monitoring depends to a considerable degree on the experience of an operator and its sensory sensitivity. In parallel, the active acidity pH in the production of rennet blobs and the Turner titrable acidity (ºT) in the production of cultured dairy product blobs are measured.
Instrumental monitoring is performed using different laboratory instruments (rheometers). For example, there is the known laboratory rheometer used to improve the recipe of dairy products and the technology of their production, namely, the Barkan geleometer , on which the “crushability” of a rennet blob at the moment of its readiness is measured via the cyclic indentation of a cone. Elastograms are obtained using a thromboelastograph, which does not give the precise kinetic picture of the formation of blobs due to the partial destruction of their structure.
A non-destructive method and a laboratory instrument for studying the coagulation of milk have been developed. The instrument consists of a temperature-controlled bath, inside which vessels filled with a milk mixture are placed on the axis connected with the electrical drive. The surface of the milk mixture in each vessel is radiated with a laser beam, which is fixed on the scales of a special screen after reflection with a photo camera fastened immovably on the instrument. The locations of reflected beams are changed proportionally to the change in the mechanostructural (rheological) properties of formed blobs upon the cyclic inclination of the vessels by the electric driver. The obtained results are used to plot “conditional rheological parameter–process duration” rheograms [5, 6].
There exist the Scott–Blair rotary elastometers and the torquemeters that are applied in the bulk method of production to monitor the structural strength of formed blobs via the rotation of a cylinder submerged into a milk mixture. In this case, the process is stopped immediately after a desired blob strength and active acidity рН = 4.5–4.7 are attained.
The common shortcoming of all the above listed devices for the monitoring of the readiness of milk–protein blobs is the absence of a control signal, which would allow these instruments to be included into an automatic process control system for monitoring the formation of milk blobs and their readiness for subsequent process operations.