Renneting of Milk Enhanced by Ultrasonic Processing

Ultrasonic milk renneting is an innovative processing technique to improve product quality and production efficiency. Ultrasound treatment applied to milk prior to coagulation has shown strong potential to optimize the renneting stage in cheese manufacturing. Low-frequency, high-power ultrasound can alter the structure of milk proteins and casein micelles, leading to improved gel formation during renneting. These effects make sonication a potent method for dairy technologists seeking to enhance milk processing operations and increase the efficiency and consistency of cheese production.

The Importance of Renneting in Cheese Manufacturing

Renneting is the critical first stage in cheese production. During this process, the enzyme chymosin cleaves κ-casein molecules, allowing casein micelles to aggregate and form a three-dimensional gel network that becomes cheese curd. The quality of this gel network directly influences:

• Gelation time
• Curd firmness
• Curd firming rate
• Microstructure and connectivity of the gel

These parameters determine how efficiently milk can be converted into cheese and ultimately influence yield, texture, and processing performance.
However, the renneting behavior of milk can vary due to factors such as protein composition, calcium balance, pH, and casein micelle structure. Technologies that improve or stabilize these properties can therefore offer significant value to dairy processors.

How Ultrasound Improves Milk Renneting

Ultrasound processing works by transmitting low-frequency ultrasound waves (>20 kHz) into liquid media. This generates acoustic cavitation, where microscopic bubbles form and collapse rapidly, creating localized mechanical forces, turbulence, and microjets in the liquid.
These mechanical effects can modify the physical structure of milk proteins without requiring high temperatures.
Research by Liu et al. (2014) demonstrated that ultrasonication of skim milk at 20 kHz prior to renneting significantly improved the gelation characteristics of milk.

The study showed that ultrasound treatment:

• Reduced the gelation time required for rennet coagulation
• Increased the rate of curd firming
• Produced stronger gels with higher curd firmness
• Improved connectivity of the rennet gel network

These improvements were attributed to ultrasound-induced changes in milk proteins and casein micelle structure.
The same findings are described in the uploaded study, which reports that milk treated with ultrasound at pH 8 and readjusted to pH 6.7 showed the most pronounced improvements in coagulation performance.

Key Structural Effects in Milk

Ultrasonic treatment alters the microstructure of milk proteins in several ways. According to the study and related research:

• Reduction of casein micelle size due to cavitation-induced mechanical forces
• Formation of smaller protein aggregates
• Increased surface area of casein particles
• Enhanced protein interactions during coagulation

These structural changes enable more efficient aggregation once rennet is added.

The results reported in the study highlight dramatic performance improvements. For example:

1. Gelation time decreased from about 40 minutes in untreated milk to roughly 28 minutes in ultrasonicated milk
2. Curd firmness increased by several times compared with the untreated control
3. The curd firming rate increased substantially

These changes translate directly into faster and more robust curd formation during cheese manufacturing.

Ultrasonic Renneting: Advantages for Dairy and Cheese Producers

For industrial dairy processing, the potential benefits of ultrasonically improved renneting are considerable.

Faster Processing

Ultrasound reduces gelation time, which can accelerate the early stages of cheesemaking.

• Shorter coagulation time
• Faster curd formation
• Potentially higher throughput in production lines

Improved Curd Structure

Ultrasonic treatment results in a denser and more interconnected protein network, producing stronger curds.

This can contribute to:

• Improved curd handling
• Better whey separation
• Enhanced texture control

Increased Manufacturing Efficiency

Stronger gels and faster coagulation may enable:

• Higher cheese yield potential
• Reduced processing time
• More consistent product quality

These advantages are particularly relevant for large-scale cheese production, where small improvements in process efficiency can translate into significant economic gains.

Ultrasound as a Non-Thermal Dairy Processing Technology

One of the most attractive aspects of ultrasonic milk processing is that it is considered a non-thermal or mild processing technology.
Unlike traditional heat treatments, ultrasound can modify the structural properties of proteins through mechanical cavitation effects, rather than high temperatures. This helps preserve the functional and nutritional characteristics of milk components.
Recent reviews highlight ultrasound as an effective and reliable technique for controlling protein functionality and gelation processes in dairy systems, including cheese and fermented milk products.
For dairy technologists, this opens opportunities to tailor milk functionality without compromising product quality.

Industrial Implementation in Dairy Plants

As research progresses from laboratory studies to industrial application, equipment reliability and food safety compliance become essential considerations.
Industrial sonication systems such as those developed by Hielscher Ultrasonics are engineered for hygienic design and safe installation in food processing environments. Such systems can be operated in compliance with cGMP and FDA guidelines, and food processing applications can be validated and certified through independent third-party testing.
Hielscher sonicators connect easily to process plant software and integrates smoothly into existing production lines. Automated data recording of the ultrasonic process parameters ensure monitoring and quality control in accordance with cGMP guidelines.
This makes ultrasonic milk processing a practical technology for commercial dairy plants seeking process innovation.
For dairy technologists and cheese manufacturers, this approach represents a reliable processing step toward more efficient, controllable, and innovative cheese production processes.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators:

Design, Manufacturing and Consulting – Quality Made in Germany

Hielscher ultrasonicators are well-known for their highest quality and design standards. Robustness and easy operation allow the smooth integration of our ultrasonicators into industrial facilities. Rough conditions and demanding environments are easily handled by Hielscher ultrasonicators.
Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.