How to measure the viscosity of gelatin with a Burgers viscometer?
I. Detection Principle
The Brookfield viscosity is calculated by measuring the flow time (in seconds) of a 6.67% gelatin solution through a standard capillary tube at 60°C to determine the dynamic viscosity (mPa·s). The core formula is:
η=k⋅ρ⋅tη=k⋅ρ⋅t
where kk is the instrument calibration coefficient, ρρ is the solution density, and tt is the flow time.
II. Instrument Preparation
Equipment Calibration
Before use, calibrate the laser ranging system and temperature sensor of the ND-2/ND-5 Brookfield viscometer using standard silicone oil.
Ensure the water bath temperature control accuracy reaches ±0.1°C, and the viscometer volume error is ≤±0.5 mL.
Sample Preparation
Weigh 6.67 g of gelatin sample, add 105 mL distilled water, and soak for 30 minutes (45 minutes for pharmaceutical gelatin).
Stir magnetically in a 40°C water bath for 30 minutes until fully dissolved, then let stand for 15 minutes to defoam.
III. Measurement Steps
Solution Injection
Inject the processed gelatin solution into the viscometer using a syringe, maintaining the liquid level 30 mm below the top of the loading section.
Pressurization and Timing
Maintain an initial pressure of 14 kPa for 2.5 minutes, then increase to 34 kPa for another 2.5 minutes, and finally adjust to the target pressure (28–69 kPa for gasoline, 69–103 kPa for jet fuel).
The laser sensor automatically records the flow time between the 152 mm marks with a precision of 0.01 seconds.
Data Output
The built-in program automatically calculates and displays the viscosity value, supporting multiple measurements for averaging.
IV. Quality Control
Temperature Control: Maintain 60±0.1°C throughout the process, monitored by dual temperature sensors.
Data Validation: Send 10% of samples monthly for third-party comparison, with critical data requiring triple verification.
Anomaly Handling: If the flow time exceeds 5000 seconds or the fluorescence interface is blurred, re-prepare the sample.
Precautions
Safety Protection: Avoid direct exposure to UV light; operate pharmaceutical-grade gelatin in a clean bench.
Standard Differences: The Brookfield viscosity limit for edible gelatin is 1.8–5.5 mPa·s, and 6.0 mPa·s for industrial gelatin.
Equipment Maintenance: Clean the capillary tube with chromic acid solution after each use and lubricate the bearings monthly.
ST-19A Digital Brookfield Viscometer is a specialized instrument designed for measuring the Brookfield viscosity of gelatin. It is manufactured in accordance with the QB2354 standard for Pharmaceutical Gelatin, while also complying with the standards QB/T1995, GB6783, GB13731, and QB/1996.
The Brookfield viscosity test of gelatin is a critical indicator for evaluating gelatin production process quality and controlling gelatin manufacturing standards. It is applicable for testing the viscosity performance of all gelatin types, including edible gelatin, pharmaceutical gelatin, industrial gelatin, and bone glue. Additionally, the instrument can be used for viscosity testing of gelatin-like liquids, such as agar and protein powders.
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