Refining pistachio paste with the Fristam FCM Colloid Mill

Trials in Italy achieved super fine micronization of pre-refined pistachio paste, with flow rates tested up to 850 kg/h.

TRIAL AN FCM

Introduction to the application and industry overview

Fine particle size and a uniform texture are key requirements in premium nut paste production. Manufacturers must balance the level of refining required for a smooth finished product with processing time, throughput and temperature control.

For pistachio processors, inline colloid mixing offers a potential route to finer texture while retaining existing upstream equipment. The Fristam FCM Colloid Mill applies intensive rotor-stator shear to reduce particle size and improve product uniformity in a continuous inline process.

Customer brief

A pistachio products manufacturer in Italy wanted to improve the productivity and the texture of its pistachio paste. Its existing refining process achieved a final particle size too coarse for premium quality products, requiring long processing times and with very limited throughput (< 350 kg/h).

The manufacturer wanted to assess whether the Fristam FCM could:

Improve the finishing texture for premium “silk” products requiring very low particle size.
Process paste at higher flow rates

Previously unsuccessful methods

The existing process combined pre-grinding of whole pistachios with a second refining stage. It produced a coarse paste without the finer particle size required for the proposed premium products.

The main limitations were extended processing times, a throughput ceiling of lower than 350 kg/h, and the impossibility to achieve a fine texture of the paste. The trial therefore focused on improving the refining stage while continuing to use the manufacturer’s existing pre-mill.

Pistachio Paste Process Machine - Fristam FCM

Fristam’s solution

Fristam’s application specialists tested the FCM Colloid Mixer downstream of the existing pre-milling equipment. As the paste passes through the narrow gap between the high-speed rotor and stator, intensive shear reduces particle size and produces a finer, more uniform texture.

The adjustable rotor-stator gap allowed the team to evaluate different settings and identify a balance between particle size reduction, overall flowrate and product temperature. . The trials assessed both the FCM’s potential to take over part of the existing refining process and its use as a final polishing stage for already-refined paste.

Trial set-up

1. Preparation of the pistachio paste
Whole pistachios were processed through the manufacturer’s existing pre-mill, which was jacketed and cooled with chilled water. A small amount of vegetable oil was added during pre-grinding to improve processability. The paste entering the FCM had a viscosity of approximately 5,000 cP.

2. Integration into the existing process
Fristam double screw FDS pump fed the paste through the FCM at flow rates up to 850 kg/h. A throttled discharge valve increased residence time in the mixer and helped improve particle size reduction.

3. Optimisation of the shear settings
In order to achieve the best overall results without the degrading the product, Fristam’s application specialists could “play” with various parameters, such as FCM rotation speed and gap opening, as well as product flowrate and discharge valve throttling.

4. Evaluation of particle size and temperature
The team compared results for paste at different incoming particle sizes. Final measurements were taken after a vibrating screen which removed remaining pistachio skin and other impurities. Product temperature was also monitored.

The trials demonstrated that the FCM could achieve particle sizes below 20 μm when the incoming paste had already undergone preliminary refining.

In one test, particle size decreased from 95 μm to 45 μm in a single pass.
In another, paste entering at 35 μm achieved a final measured particle size of 9 μm after FCM processing and vibrating screening.
Trial flow rates reached 850 kg/h, more than twice the existing ball-mill system’s maximum throughput of around 350 kg/h.

The trial in Italy achieved a significant particle size reduction on pre-milled pistachio paste, with improved emulsion quality and texture compared with the existing process. Inline flow rates were tested up to 850 kg/h, supporting the FCM’s potential as a final polishing stage for premium pistachio paste or a partial replacement for conventional refining technologies. The Customer was impressed by the results obtained and after the trials purchased a new FCM Fristam Colloid Mill.

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Process/Product benefits

Finer particle reduction: A very low particle size was achieved for premium “silk” products.
Improved texture: The trial report recorded a finer emulsion and improved texture compared with the existing ball-mill process.
Higher trial flow rates: The FCM was tested up to 850 kg/h.
Adjustable refining intensity: Gap adjustment allowed the team to balance particle reduction against temperature rise.

Sustainability benefits

The trial explored an upgrade that retained the customer’s existing pre-milling equipment, offering a potential route to make continued use of installed process infrastructure.

Processing was faster, reducing energy consumption.

Financial benefits

Potential capacity improvement: Higher flow rates reduce the refining bottleneck.
Targeted process investment: The FCM can be retrofitted into the process to improve it, reducing CAPEX costs.
Premium product development: The results support further market expansion for finer-textured pistachio products

Other benefits

On-site application support: Testing took place at the manufacturer’s facility with Fristam specialists under actual site conditions.

Similar applications

The results suggest potential for other nut and seed processing applications where fine particle size, smooth texture and consistent product uniformity are important. These include:

Hazelnut and almond pastes for confectionery, bakery fillings and dessert ingredients.
Peanut butter and other nut butters, including cashew and mixed-nut spreads, requiring a finer texture.
Praline pastes, chocolate–nut spreads and confectionery fillings where particle reduction contributes to a smooth mouthfeel.
Tahini and sesame paste, as well as sunflower and pumpkin seed pastes, requiring fine grinding and uniform consistency.
Nut-based creams and dessert sauces where refining and homogenization may improve finished texture.

For manufacturers looking to refine nut paste, reduce graininess in nut butter or improve seed paste texture, the FCM could be evaluated as an inline polishing stage or a partial alternative to ball-mill refining.

Frequently Asked Questions

Yes. In this trial, pre-refined paste with coarse particle size achieved a final measured particle size below 20 μm after FCM processing and vibrating screening.

Discuss your particle size, texture and throughput requirements with Fristam’s application specialists.

In addition to mixing & blending technology – check out Fristam’s full range of pumping technologies suitable for various industries.

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Refining pistachio paste with the Fristam FCM Colloid Mill