Skip to main navigation Skip to main content Skip to page footer
amixon GmbH amixon GmbH
Amixon
Request a mixing trial
Contact

Which criteria are decisive for selecting a spice mixer for different particle sizes (peppercorns to powder)?

Selecting a mixing system for spices with very different particle sizes – from whole peppercorns to fine powders – depends on process-engineering, product-specific and hygienic requirements. The key criteria are:

Mixing principle and mixer geometry

  • For mixtures with a wide particle-size spectrum, convective mixers (e.g. ploughshare, paddle, blade or ribbon mixers) are usually the first choice, since active material displacement and three-dimensional restratification reduce segregation effects. Diffusive free-fall mixers (e.g. drum mixers) tend towards segregation with strongly differing particle sizes and densities.

Preventing segregation

  • Very different particle sizes and densities favour phenomena such as the "Brazil nut effect", in which coarse particles migrate upward. A suitable mixer:
  • operates with low Froude numbers (limited acceleration of the product bed),
  • avoids long settling phases and dead zones,
  • enables short, reproducible mixing times to limit percolation and trajectory segregation.

Equally important is the emptying design: large outlet cross-sections with virtually complete residual emptying minimise funnel formation and renewed segregation during discharge.

Gentle product handling and particle protection

  • Whole peppercorns, dried herbs and other coarse fractions should retain their structure, while essential oils and other aroma components are protected from excessive thermal or mechanical stress. The mixer should therefore:
  • have variable speed control,
  • be designed to avoid particle breakage, abrasion and excessive frictional heating (if necessary with cooling options such as a double jacket),
  • work with mixing tools that mix sufficiently without generating high shear forces.

Fill level, batch size and homogeneity

  • The mixer must ensure high mixing quality over a defined fill-level range. For horizontal mixers, the optimum fill level typically lies in the range of roughly 40–70% of the usable volume; at the same time, the design should still ensure good mixing even at smaller batch sizes. Coefficients of variation (CV) ≤ 5% are frequently required for spice blends – the mixer must achieve this homogeneity reproducibly, even when trace-level micro-components are added.

Cleanability and hygienic design

  • Since spice processes involve frequent recipe and allergen changes (e.g. mustard, celery), the following are:
  • dead-space-free, low-gap designs,
  • polished surfaces (typically Ra ≤ 0.8 µm),
  • good accessibility of seals and mixing components,
  • CIP/COP capability and complete residual emptying
  • essential in order to avoid cross-contamination and reduce downtime during product changeover.

Integration of liquid and micro-components

  • Many spice blends contain oils, oleoresins or other liquid components for aroma-carrier function or dust binding, as well as micro-components with a very low mass fraction. A suitable mixer provides:
  • facilities for fine liquid distribution (e.g. spray lances or atomising nozzles in zones of high turbulence),
  • defined inlet points for very fine substances and small components, so that they are captured quickly and evenly,
  • the possibility of staged addition (main fractions first, then small and liquid components).

Mode of operation and scalability

  • The choice between batch and continuous operation depends on the number of recipes and the desired throughput:
  • Batch mixers are advantageous for frequent recipe changes and flexible lot sizes.
  • Continuous mixers are suitable for constant product streams with unchanging composition and high throughputs.

For transferring laboratory or pilot-plant trials to production, the mixer should be geometrically similar and exhibit comparable Froude numbers, so that mixing kinetics and product quality remain scalable and reproducible.

Safety and dust-explosion protection

  • Fine spice powders can form explosible dust-air mixtures. Depending on the dust class and operating conditions, an ATEX-compliant design with suitable structural protective measures (e.g. pressure-shock resistance, relief devices) may be required.

In practice, these criteria are assessed together: the right mixing system for peppercorns through to powders must simultaneously ensure high homogeneity, low segregation tendency, gentle product handling, hygienic cleaning, flexible handling of different batch sizes, and the integration of liquid and micro-components.

How amixon® masters large density and particle-size differences when mixing

Space-controlling mixing tool instead of random movement

With large density differences, mixing principles that rely on free bulk-material movement fail: heavy particles sediment, light particles float, and centrifugal forces classify. The amixon® SinConvex® helical-ribbon mixing tool, by contrast, controls the entire mixing chamber: it forcibly conveys the mix upward at the periphery and lets it flow downward under gravity at the centre. Every particle passes through the same forced flow – regardless of density, size or flow behaviour. The low-speed operating mode (approx. 0.8–3.5 m/s peripheral speed) avoids centrifugal separation of fine or light constituents.

Practical evidence: powder metallurgy

In powder metallurgy, amixon® twin-shaft mixers (HM, with a reference unit up to size HM 16000 at 16 m³) distribute pressing aids such as zinc stearate homogeneously in metal powder – at bulk densities of around 4 kg/dm³ for the metal powder and less than a twentieth of that for the metal soaps, at particle sizes of 2 to 70 µm. More extreme density ratios are hardly ever encountered in practice.

An all-rounder for heterogeneous compositions

The Gyraton® GM is also explicitly designed for heterogeneous material compositions: coarse and fine particles, differing bulk densities, flow properties and moisture contents – up to a batch size of 100 m³. The result is always the technically ideal random mixture, independent of fill level from as little as approx. 10% filling onward.

Verification in the pilot plant

Whether the specific combination of density spread, particle-size distribution and cohesion delivers the expected result is verified by amixon® beforehand in the pilot plant: mixing trials with the original product on more than 30 test units, with sampling and documented assessment of mixing quality – the basis for machine sizing.

For tea, herbs and spices, amixon® mixes with particular care: the low-speed operating mode preserves fragile leaves and particles, while virtually complete emptying and fast cleaning enable frequent recipe changes; the Gyraton® GM homogenises spices, tea and coffee even in large batches of up to 100 m³.

Hygienic design as the constructional basis

All of the properties described rest on the amixon® Hygienic Design: the mixing chamber and mixing tool are seamlessly welded and ground, and the mixing tool is supported only at the top – eliminating the contamination-critical lower shaft feed-through. Large Clever-Cut®-inspection doors with a permanently dead-space-free OmgaSeal® seal make all product-contact surfaces ergonomically accessible; dead-space-free outlet fittings and integrated wash lances (fully automatic wet cleaning on request) make both dry and wet cleaning validatable – in accordance with EHEDG guidelines, FDA hygiene guidelines and 3-A Sanitary Standards.