Estimated reading time: 6 minutes
During one of its recent monthly webinars, the Dairy Standard Agency (DSA) explored dairy cultures, common fermentation challenges, and practical solutions. Jompie Burger, managing director of the DSA, shared guidelines designed to address production issues in fermented dairy products while emphasising the importance of accurate data recording to support effective problem assessment.
Burger said systematic, practical problem-solving is fundamental to maintaining product quality. A thorough understanding of the dairy value chain is essential, as many production issues are quality deviations rather than food safety concerns. These deviations can, however, still result in costly product recalls and financial losses. Hence, he stressed the importance of proactive management to identify and mitigate risks before they affect the entire value chain.
Direct observation on the production floor is one of the most effective ways to identify the root cause of a problem. Culture-related troubleshooting should follow a structured process from the outset. This systematic approach is applicable across the food processing industry and aligns with quality management systems such as ISO 9001 and modern food safety programmes.
A practical approach
Burger outlined a seven-step problem-solving process:
- Identify the problem.
- Understand the interests of all stakeholders.
- List possible solutions.
- Evaluate each option based on risk and potential impact.
- Select the best solution.
- Document the agreed course of action.
- Implement control measures, supported by monitoring and contingency plans.
A common production challenge discussed during the webinar was slow acid development in the fermentation tank. Table 1 lists the factors influencing the acidification curve, which depends on bacterial growth occurring within a specified timeframe to achieve the desired product profile.
Table 1: Factors influencing the acidification curve. (Source: DSA)
| Information to be provided | Steps that can be followed* |
| Addition of starter culture. | Add more starter culture if an error is suspected during the initial addition of culture. |
| Enough starter culture added – only lowers the pH of the milk. | Increase the number of cells. |
| Milk tested for antibiotics/inhibitors. | Extend the ripening period. |
| Bacteriophage levels in the facility. | Postpone the addition of salt. |
| Rotation of cultures. | For buttermilk, cottage cheese and sour cream, the tank can be corrected by adding a DVS culture, provided this is done well before the protein starts to precipitate. |
| Culture storage conditions. | Monitor the growth curve closely and correct it immediately upon detecting any deviation from the expected growth pattern. |
| Has sufficient time been allowed for ripening? | Increase the thoroughness of disinfection for all subsequent cheese vats. |
| Does the process gradually slow down throughout the day? | |
| Do the delays occur in a particular cheese vat or are they associated with a specific starter culture tank? | |
| Cleaning and disinfection schedule. |
*Depending on the extent of the delay.
Too slow or too rapid acidification affects bacterial performance, which prevents the product from developing correctly. Burger also explained that direct vat set (DVS) cultures are highly concentrated, freeze-dried or frozen bacterial cultures that are added to milk to initiate the fermentation process.
Finished product deviations
Deviations in the final product are another source of production issues. These are usually identified during sensory evaluation, when the quality team assesses the product’s texture, flavour, and appearance. Burger highlighted five key guidelines for identifying these issues.
Poor product structure: A common concern is cheese that is too soft or shows signs of separation. To identify the cause, evaluate moisture and fat content, process variations, manufacturing methods, proteolysis, culture balance, and microbiology. If the culture performs according to specification, the next step is to assess the milk’s quality and verify that the correct heat treatment was applied during pasteurisation.
To achieve the necessary protein changes, yoghurt is typically heated to around 80°C, and amasi to 85°C for a few seconds. The manufacturing process must suit the specific culture. Avoid excessive vibration and rough handling of milk during critical processing stages. Transporting milk in crates, subjecting it to hard impacts, or pumping it through vibrating pipelines can mechanically damage milk proteins. Heat treatment reduces the ability of protein and fat to bind, which compromises the structure of the final product.
Viscosity: The fat-free solids, total solids and fat content of the incoming milk must meet specified requirements. Other factors to evaluate are fermentation temperature and duration, pasteurisation and heat treatment, culture characteristics, bacteriophage levels, and adherence to critical process specifications.
Gas formation: Excessive gas formation is a serious quality defect. In cultured dairy products, it is important to evaluate fermentation time and temperature, solids levels, citrate usage, post-pasteurisation contamination, and milk quality. In cheese production, the aspects that require evaluation are milk quality, heat treatment, pasteurisation, post-pasteurisation contamination, the presence of non-starter lactic acid bacteria in the facility, ripening conditions, and culture selection. Culture selection, in particular, plays a key role in the fermentation process.
Insufficient gas formation: Assess culture selection and fermentation time and temperature in cultured dairy products. In cheese production, factors to investigate include the addition of propionic acid bacteria cultures, correct ripening conditions, adequate starter culture growth, moisture content, the use of selected cultures where applicable, manufacturing practices, and the handling and pumping of the curd.
Off flavours: Off flavours can result from several factors, including solids levels, bacteriophage activity, temperature fluctuations, fermentation times, an imbalance of beneficial bacterial strains, psychrotrophic bacteria, culture selection, and milk quality.
In cultured dairy products, milk age and quality, microbiological load, stabilisers, added flavours, and any potential contamination must be evaluated. With cheese, the investigation should focus on milk quality and age, microbiological load, fat replacers, whey expulsion, and possible contamination. Poor-quality or old milk, high microbial counts, stabilisers, added flavourings, contamination, fat replacers, and inadequate whey expulsion can all contribute to undesirable flavours.
Burger stressed the importance of a step-by-step approach to troubleshooting rather than attributing problems to a single cause. Evaluate the entire process, record observations, verify deviations, and implement corrective actions that address the root cause.
Minimise errors
Most production issues stem from human and environmental factors. Infrastructure such as doors, windows, and air-conditioning systems must be managed to maintain correct airflow and positive air pressure within specified limits. Bacteriophages pose a major risk, along with raw milk quality. During milk shortages, extra care is needed when sourcing milk from unverified suppliers. Be sure to select the correct culture and continually monitor its performance.
Burger stressed the importance of routine inspections, thorough pre-production checks, and ongoing monitoring throughout the day. Personnel must be properly trained and held accountable. Prevent cross-contamination from personnel, equipment, and cleaning practices, and use only approved raw materials. Assess any deviations before implementing changes.
“Quality is everyone’s responsibility, including management, which must actively support compliance. Following a standardised problem-solving process is far more effective than making ad hoc decisions,” he stated.
Most product defects, he explained, can be traced to a few key areas, such as raw material quality, heat treatment, manufacturing practices, culture handling, and hygiene. Personnel must act as custodians of these control points. Integrated value chain management, supported by open communication between departments, is essential to ensure that the entire production chain works together to maintain food safety and product quality. – Christal-Lize Muller, Stockfarm
For more information, email Jompie Burger at jompie@dairystandard.co.za or visit www.dairystandard.co.za to watch the webinar.
