Spongy Coliform Defect In Cheese (Causes & Prevention)

Imagine slicing into a beautiful wheel of cheese, only to find it riddled with irregular, sponge-like holes. Instead of the smooth texture and delightful aroma you expect, you’re hit with sourness and an unpleasant odour. For cheesemakers, this nightmare has a name: spongy coliform. But how does it happen, and what can be done to prevent it?

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What is spongy coliform?

Spongy coliform is a defect in cheese caused by coliform bacteria such as Escherichia coli and Enterobacter. These bacteria ferment lactose, producing gas and acids that disrupt the cheese structure.

The defect is classified as a type of early blowing, occurring during or shortly after fermentation. It is characterised by small, irregular holes and an unpleasant flavour or odour. Spongy coliform can affect both soft and hard cheeses, making it a concern for a wide range of cheesemakers.

Another type of early blowing can be due to yeast contamination. And the most common type of late blowing is due to Clostridia bacteria. We’ll dive into the differences a bit further down.

What are coliform bacteria?

Coliform bacteria are Gram-negative, rod-shaped microorganisms that can contaminate cheese during production. They are naturally present in soil, water and the intestines of warm-blooded animals. While many coliforms are harmless, their presence in cheese often indicates poor hygiene or contamination during processing.

Coliforms in cheese are generally categorised into two groups:

1. Total coliforms

• These are all coliform bacteria commonly found in the environment.
• Examples include Enterobacter, Klebsiella and non-pathogenic strains of Escherichia coli (E. coli).
• While not all are harmful, their presence in cheese signals lapses in sanitation.

2. Faecal coliforms

• A subset of coliforms originating from the intestines of animals.
• Includes strains like E. coli, often used to detect faecal contamination.
• Some strains, particularly pathogenic ones like E. coli O157:H7, pose serious health risks if present in cheese.

Understanding these bacteria helps cheesemakers address contamination risks and maintain the highest standards of safety and quality.

Causes of spongy coliform

Spongy coliform typically arises from contamination during cheesemaking. Common causes include poor milk quality, insufficient pasteurisation and unsanitary equipment.

1. Poor milk hygiene: Raw milk often contains coliform bacteria, especially if it comes from animals kept in unsanitary conditions. Contaminated milking equipment can worsen the problem. Even small amounts of coliform bacteria in milk can multiply during cheesemaking.
2. Improper pasteurisation: Pasteurisation kills most bacteria, but it must be done correctly. If the milk is not heated to the right temperature, coliforms may survive. These surviving bacteria can thrive during the cheesemaking process.
3. Dirty cheesemaking equipment: Cheesemaking tools and surfaces must be thoroughly cleaned and sanitised. Contaminated equipment can introduce coliforms to the milk or curd. Bacteria on utensils or vats can spread quickly, affecting entire batches of cheese.

How to identify spongy coliform defects

Cheesemakers should look for certain signs to identify spongy coliform. These include:

• Irregular, sponge-like holes in the cheese body.
• Sour and acidic notes
• Faecal or barnyard smells
• Rancid or soapy flavours
• Bitter aftertaste

Testing milk and curds can also help detect coliform bacteria early. Laboratory tests can measure coliform counts to assess milk quality.

Spongy coliform vs yeast contamination vs late blowing

Cheese defects like spongy coliform, early blowing caused by yeast and late blowing are common challenges for cheesemakers. Each defect results from different microbial activity, impacting texture, flavour and overall cheese quality. Understanding the causes, timing, and prevention strategies is crucial to maintaining high production standards.

This guide compares these three defects, highlighting their key differences to help cheesemakers identify and address them effectively.

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How spongy coliform creates a sponge-like texture

The sponge-like texture in cheese caused by coliform bacteria is primarily the result of gas production during fermentation. This process is driven by the bacteria’s metabolism and their interaction with the cheese’s components. Here’s how it works:

Coliform bacteria metabolism

• Coliform bacteria, such as Escherichia coli or Enterobacter, thrive in nutrient-rich environments like cheese curds.
• These bacteria ferment lactose (milk sugar) and other available carbohydrates.
• The by-products of this fermentation include:
  • Carbon dioxide (CO₂): A gas that forms bubbles within the cheese matrix.
  • Organic acids (e.g., acetic and lactic acids): These can further alter cheese texture and flavour.

Formation of gas pockets

• As CO₂ is produced, it becomes trapped in the dense protein structure of the curd.
• The gas cannot escape easily, leading to the formation of irregular holes or bubbles.
• Unlike the controlled eye formation in Swiss cheese, these gas pockets are uneven and chaotic, resulting in the “spongy” appearance.

Impact on protein structure

• The activity of coliform bacteria can also weaken the protein network in cheese.
• Enzymes secreted by the bacteria may break down casein, the primary milk protein.
• This degradation contributes to a softer, less cohesive texture, making the cheese feel sponge-like.

Environmental factors that exacerbate the issue

Several conditions in the cheesemaking process can amplify the effects of coliform bacteria:

• Temperature: Warm temperatures during early stages encourage rapid bacterial growth and gas production.
• pH Levels: Coliform bacteria thrive in slightly alkaline environments, which can occur if proper acidification doesn’t take place.
• Moisture Content: High moisture levels provide an ideal medium for bacterial activity, increasing the risk of spongy defects.

Chemical reactions in cheese

• Over time, the texture becomes more irregular as the curd stretches and collapses around the gas pockets.
• The acids produced by coliform bacteria can disrupt the delicate balance of calcium and phosphate in cheese.
• This imbalance weakens the curd structure, allowing gas to accumulate more freely.

How unpleasant smells and flavours arise from coliform contamination

When coliform bacteria contaminate cheese, they produce a range of metabolic by-products during fermentation. These compounds are responsible for the unpleasant smells and flavours associated with spongy coliform defects. Here’s a breakdown of how this occurs:

1. Fermentation of lactose

Coliform bacteria ferment lactose, the primary sugar in milk, producing:

• Acetic acid: Contributes sour, vinegary flavours.
• Lactic acid: Adds an overly tangy or sour taste if produced in excess.
• Carbon dioxide (CO₂) and hydrogen gas: While these gases affect texture, they can also carry volatile compounds that intensify odours.

2. Production of volatile compounds

During fermentation, coliform bacteria generate volatile organic compounds (VOCs), which contribute to odour and flavour. Examples include:

• Diacetyl: Often associated with buttery flavours, but in excess can taste rancid or harsh.
• Ammonia: Produced during protein breakdown, giving a sharp, unpleasant smell.
• Sulfur compounds: Result in rotten egg or sulphurous odours.

3. Protein breakdown (proteolysis)

Coliform bacteria release enzymes that degrade milk proteins like casein. This process creates:

• Amines (e.g., putrescine and cadaverine): Responsible for strong, faecal or rotting odours.
• Peptides and amino acids: While these are normal in cheese ripening, their breakdown by coliforms produces bitter or astringent flavours.

4. Fat breakdown (lipolysis)

Coliform bacteria can also break down fats in the cheese, producing:

• Free fatty acids: These contribute to rancid or soapy flavours.
• Ketones: Compounds like methyl ketones can add strong, unpleasant aromas.

5. Environmental influence

• Moisture and Temperature: Warm, humid conditions accelerate bacterial metabolism, intensifying the production of odorous and flavour-altering compounds.
• pH Levels: High pH environments, often resulting from coliform contamination, enhance the activity of enzymes that produce these unpleasant by-products.

Preventing spongy coliform in cheese

Preventing spongy coliform requires strict attention to hygiene and cheesemaking techniques. Cheesemakers should follow these steps to minimise risk:

• Source high-quality milk: Start with milk from trusted suppliers. Farmers should ensure animals are kept in clean environments. Milking equipment must also be regularly cleaned and sanitised.
• Use proper pasteurisation techniques: Milk must be pasteurised at the correct temperature and time. This process eliminates most bacteria, including coliforms. Ultra-pasteurisation can be an option for some cheese types.
• Maintain rigorous sanitation: Cheesemaking equipment, tools, and surfaces must be cleaned and sanitised after each use. Steam or chemical sanitisers can effectively kill bacteria. Regular testing of equipment can identify contamination risks.
• Use reliable starter cultures: Starter cultures play a key role in cheese fermentation. They help outcompete undesirable bacteria like coliforms. Choose cultures that are well-suited to the specific cheese being made.
• Monitor pH levels carefully: Maintaining the correct pH during cheesemaking is critical. Coliform bacteria thrive in higher pH conditions. Acidification of the milk and curd can help prevent their growth.

What to do if spongy coliform occurs

Spongy coliform can be devastating for a cheesemaker, but taking prompt and effective action can mitigate the damage. Here’s how to handle an outbreak of spongy coliform:

1. Identify the affected cheese: Examine your cheese for signs of spongy coliform. Look for small, irregular holes and check for sour or rancid smells.
2. Dispose of the affected cheese: Unfortunately, cheese with spongy coliform cannot be salvaged. Discard the affected batches responsibly to prevent cross-contamination. Consider composting the cheese for an eco-friendly disposal.
3. Trace the contamination source: Investigate where the contamination might have occurred. Test raw and pasteurised milk for coliform bacteria levels. Review cleaning and sanitisation procedures for equipment and facilities. And verify the integrity and effectiveness of the starter cultures used.
4. Clean and sanitise thoroughly: Coliform bacteria can persist in cheesemaking environments, so deep cleaning is essential.
5. Test subsequent batches: Before resuming production, test the next few batches for signs of coliform bacteria. Conduct microbial testing on milk, curds, and early-stage cheese. And monitor for abnormal gas formation or pH changes during fermentation.
6. Implement stricter controls: Take this opportunity to improve practices to reduce the risk of recurrence: use higher-grade milk from trusted sources, adjust pasteurisation parameters to ensure coliforms are eradicated and increase the frequency of hygiene checks and microbial testing.
7. Document the incident: Maintain detailed records of the incident, including test results, affected batches, and corrective actions taken. This documentation can help track patterns, demonstrate compliance, and avoid regulatory issues.

By acting decisively and addressing the root cause, cheesemakers can recover from spongy coliform outbreaks. More importantly, these steps help ensure the problem doesn’t happen again.

Conclusion

Spongy coliform is a challenging defect that can harm both cheese quality and a cheesemaker’s resolve. However, it can be prevented with proper milk handling, sanitation and pasteurisation. By understanding the causes and implementing strict hygiene standards, cheesemakers can produce high-quality, defect-free cheeses.

Cheesemaking is both an art and a science. With knowledge and care, you can ensure that every wheel of cheese meets the highest standards.

Jonah Kincaid

Cheese lover. Scientist. Created a website and a Youtube channel about cheese science because he could not find answers to his questions online.