Rheological properties of coffee powder

USE

Determination of the flow characteristics of ground coffee powder.

TEST EQUIPMENT

Instrument: Powder Flow Tester (PFT)

Tank: 230 cc, 6 inches in diameter

Lid Type: Pallet Lid, 304 s / s, 33 cc, 6 inch diameter

Test type: Flow function

Test temperature: Ambient temperature (70-72 ° F)

Humidity: 48 %

TEST METHOD

A Brookfield powder flow tester equipped with Powder Flow Pro software for automated instrument control and data acquisition was used to test the ground coffee. The coffee was picked up in the trough and the scraping tool was then used to evenly distribute the powder and form the sample. After recording the sample weight and entering it into the software, a standard flow function test was performed. The time required for the test was 25 minutes.

MEASURED PARAMETERS

Fluidity: easy flow

Bulk density: 308 kg / m³ (filling density) to 399 kg / m³ (final bulk density)

TO ANALYSE

Hopper shape:

conical arch Flow factor: 0.119 m (119 mm; 4.6 in)

Rathole diameter: 0.567 m (Tank diameter - 2 m)

RESULTS

Figure 1 shows the fluidity of ground coffee at different levels of consolidation stress. These results show that coffee generally flows easily at all levels of consolidation constraints. However, the material gains strength as the feed system empties and becomes cohesive at the lowest consolidating stress.

Note: Flow function data is indicated by the red line. The other lines are references (or “Standard Flow Indices”), which distinguish the different types of flow behavior, ranging from “non-fluid” to “fluid”.

The axes are the unconfined breaking strength (kPa) with respect to the major principle consolidating stress (kPa).

Figure 1: Ground coffee flow function graph

Figure 2 shows the dimension of the vault and the diameter of the rat hole (based on a standard bin diameter of 2 meters and a bin height of 8 meters). Ground coffee, based on the dimension of the arch, requires an opening of at least 0.119m. To avoid the formation of a rat hole, an opening of 0.567 m is necessary. The diameter of the rat hole is normally used as an indicator of fluidity.

Figure 2: Arch dimensions and through hole diameter

Figure 3 Figure 3 shows the bulk density of the material at different levels of consolidation stress. This graph tells us that ground coffee has a fill density of around 308 kg / m³ and amounts to around 399 kg / m³ at 12.685 kPa of consolidation stress. In general, a free flowing powder will show very small changes in bulk density, while a cohesive or low flowing powder will generally show a large increase in bulk density. This ground coffee has a

lower increase in bulk density, indicating that this powder flows easily.

The axes are the apparent density (kg / m3) compared to the consolidation stress of the major principle (kPa).

Figure 3: Bulk density graph of ground coffee

CONCLUSION

Ground coffee is a powder that flows easily to the lowest consolidating stress, at which point it becomes cohesive. Ground coffee becomes more and more cohesive as the feed system drains, so it may experience flow issues. However, these should be minor as the material usually flows easily. The values for the arch dimension and the rathole diameter indicate a material that will be generally easy to pour.