Which process windows for fill level, speeds and mixing times are typical for achieving below 5 % RSD with spices?
A coefficient of variation of the mixing quality of approximately 5 % is regarded with spice blends as a practical target value for a particularly uniform distribution of all components. Depending on the category of mixing system, the fill level, the rotational speed, the mixing time, the adaptation to the formulation as well as the particle size, the moisture and the fat content are decisive factors.
The fill level influences particle movement and the mixing zones. With convective mixers the typical values lie at 40 to 70 %, frequently in the range of 50 to 60 %. With free-fall mixers, 40 to 60 % are customary, and with vertical mixers often 50 to 80 %.
The rotational speed must be chosen so that good blending arises without segregation or product damage being encouraged. Convective intensive mixers frequently work with a circumferential speed of 1 to 3 m/s, ribbon mixers with approximately 0.5 to 1.5 m/s. Choppers are switched in at a high rotational speed where required, in order to break up agglomerates.
Intensive mixers (ploughshare mixers and vertical helical mixers) often achieve good homogeneity after as little as 60 to 300 seconds. Horizontal ribbon and free-fall mixers usually require longer, often 5 to 15 minutes. With liquid additions such as oils or flavourings, additional short mixing phases with chopper support are frequently added.
It is important to hit the mixing end point before segregation sets in. In practice, an RSD below 5 % is generally achieved through preliminary trials, a suitable addition strategy and process management adapted to the formulation.
How amixon® achieves the highest mixing qualities (coefficient of variation below 5 %) – even with micro-dosing
The ideal random mixture is a system property of the amixon® precision mixers
amixon® precision mixers produce a technically ideal random mixture that cannot be further improved in practice. CV targets below 5 % can thereby be demonstrated robustly. Micro-dosing of vitamins, enzymes or trace elements can also be homogenised in this way, even at very large mass ratios.
The mixing quality is largely independent of the fill level. It makes no difference whether a mixer is operated with a large or a small batch – the result is always an ideal random mixture. Different batch sizes can therefore also be processed without re-evaluating the mixing stage. The fill level can be selected within a broad range.
The circumferential speed is adjustable and the mixers are generally operated at low speed and with negligible heat input. Sensitive carriers, coatings and encapsulated active substances thereby remain largely intact. A switchable cutting rotor can break up agglomerated premixes in a targeted manner without unnecessarily loading the entire batch. Centrifugal segregation is avoided by the principle itself.
The target values are checked in the pilot plant with the original product. Samples are taken strategically for this, and the results are documented and evaluated. The mixing quality can thereby be secured robustly before the investment.
Hygienic design as the constructional basis
All the properties described rest on a hygienic design concept. Surfaces welded free of crevices and ground smooth, the top-mounted bearing of the mixing tool as well as discharge devices with few dead spaces facilitate cleaning and validation. Large inspection doors and integrated washing systems support dry and wet cleaning in accordance with the hygiene requirements.