Imagine this: you’ve waited months to enjoy a perfectly aged wheel of cheese, only to discover bulges, cracks or an unpleasant smell when you unwrap it. This heart-breaking scenario is caused by late blowing, a defect that can ruin even the most carefully crafted cheeses. For home cheesemakers, understanding late blowing is essential to preserving both your cheese and your peace of mind.
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What is late blowing?
Late blowing occurs when gas-producing bacteria multiply in cheese during ageing. This gas causes the cheese to swell, crack or develop an irregular texture. The problem often arises weeks or months after the cheese has been made, hence the term “late blowing.”
Causes of late blowing
Late blowing is primarily caused by Clostridium tyrobutyricum, a spore-forming bacterium found in soil, silage or contaminated milk. These bacteria thrive in anaerobic environments, converting lactate into butyric acid and gas, which creates the characteristic defects.
Key causes of this contamination include:
- Poor milk hygiene: Contaminated raw milk or milk from cows exposed to silage can introduce Clostridium spores.
- Improper sanitation: Unclean equipment can harbour bacteria that contribute to late blowing.
- Inadequate starter culture: Weak or insufficient starter cultures may fail to outcompete unwanted bacteria.
- High moisture content: Excess moisture in cheese creates an ideal environment for Clostridium growth.
- Improper salt levels: Salt inhibits bacterial growth. Insufficient salting can allow harmful bacteria to thrive.
Other clostridium species causing late blowing
While Clostridium tyrobutyricum is the most common culprit of late blowing, other Clostridium species can also contaminate cheese and cause similar issues. These include:
- Clostridium butyricum: Similar to C. tyrobutyricum, this species ferments lactate to produce butyric acid, carbon dioxide and hydrogen gas. It thrives in anaerobic conditions and is often linked to silage-fed cows.
- Clostridium sporogenes: This bacterium can cause gas formation in cheese but is less common. It produces spores that survive pasteurisation and grow in low-oxygen environments during ageing.
- Clostridium beijerinckii: Although rare in cheesemaking, it can cause gas-related defects in dairy products. Like other species, it thrives in high-moisture and low-salt conditions.
- Clostridium perfringens: While primarily a pathogen associated with foodborne illness, C. perfringens spores can occasionally contaminate milk. It’s not a typical cause of late blowing but may produce gas and spoilage in improperly handled cheese.
Is Clostridium botulinum a risk in cheesemaking?
Clostridium botulinum is a serious foodborne pathogen known for producing botulinum toxin, one of the most potent toxins. While it is more commonly associated with improperly canned or preserved foods, it can pose a risk in cheesemaking under specific conditions.
Conditions for Clostridium botulinum growth
For C. botulinum to grow and produce toxins, it requires:
- Anaerobic environments: Like other Clostridium species, C. botulinum thrives in low-oxygen conditions, such as vacuum-sealed or waxed cheese.
- Moisture: High-moisture cheeses are more susceptible because water activity facilitates bacterial growth.
- Low acidity: C. botulinum struggles to grow in acidic environments (pH below 4.6). Most cheeses fall within a safe pH range after proper acidification.
- Inadequate salt levels: Salt inhibits bacterial growth, but insufficient salting can allow C. botulinum to proliferate.
Is C. botulinum a common concern in cheese?
Clostridium botulinum contamination is rare in cheese because:
- Proper cheesemaking lowers pH to levels that inhibit C. botulinum growth.
- Most cheeses are salted adequately, creating an inhospitable environment for the bacteria.
- Pasteurisation kills vegetative cells, though spores can survive and grow later if conditions allow.
Preventive measures for all clostridium species
Since several Clostridium species can lead to late blowing, it’s vital to adopt broad preventive strategies:
- Improve milk quality: Use clean, high-quality milk from cows not exposed to silage.
- Sterilise equipment: Proper sanitation helps minimise all forms of bacterial contamination.
- Add lysozyme: This enzyme effectively inhibits multiple Clostridium species.
- Monitor salt and moisture: Low salt and high moisture create ideal conditions for anaerobic bacteria.
By taking these precautions, you can reduce the risk of late blowing caused by any Clostridium species.
Can yeast cause late blowing?
While yeast is not the primary cause of late blowing, certain yeast strains can contribute to similar defects in cheese. Yeast contamination during the cheesemaking or ageing process can lead to gas production, resulting in swelling, cracks or other undesirable changes.
How yeast contributes to late blowing:
- Gas production: Some yeast strains, such as Candida or Saccharomyces species, ferment lactose or residual sugars in cheese, producing carbon dioxide and other gases. This can mimic the effects of Clostridium species, particularly in cheeses with high moisture content.
- Altered microbial balance: Yeast growth can disrupt the balance of the starter culture, weakening the ability of beneficial bacteria to dominate. This may indirectly encourage Clostridium or other harmful bacteria to proliferate.
Distinguishing the contaminants that can cause blowing in cheese
Early and late blowing defects can both cause gas formation and irregular holes in cheese, but their causes and characteristics differ. The most common cause of early blowing is coliform contamination which can cause a defect called spongy coliform.
Let’s take a look at the main differences between late blowing, yeast contamination and spongy coliform.
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| Aspect | Spongy Coliform | Yeast Contamination | Late Blowing |
|---|---|---|---|
| Cause | Caused by coliform bacteria (e.g., E. coli). | Caused by certain yeast species (Candida, Kluyveromyces). | Caused by Clostridium tyrobutyricum. |
| Fermentation Type | Ferments lactose, producing gas & acids. | Ferments residual lactose or other sugars, producing gas. | Ferments lactate, producing butyric acid and gas. |
| Gas Formation | Produces small, irregular, sponge-like holes. | Produces gas, but holes may vary in size or distribution. | Produces large, round or cracked openings. |
| Timing | Occurs early, during or shortly after fermentation. | Occurs early but may also affect the initial ripening stages. | Happens late, typically during cheese ageing. |
| Flavour & Aroma | Produces sour, rancid or faecal smells & flavours. | Can produce alcoholic, fruity or yeasty flavours & odours. | Creates a strong butyric acid aroma (rancid, cheesy smell). |
| Prevention | Ensure proper milk quality, pasteurisation & hygiene. | Control yeast levels, proper sanitation, & balanced starter cultures. | Use silage-free feed, add lysozyme, & reduce spore contamination. |
Cheeses most commonly affected by late blowing
Late blowing is most frequently observed in hard and semi-hard cheeses. These styles undergo prolonged ageing, providing an ideal environment for gas-producing bacteria like Clostridium tyrobutyricum. Here are some examples of cheeses commonly affected by late blowing:
- Gouda: Gouda is one of the cheeses most associated with late blowing. Its moderate moisture content and long aging process create conditions that can allow Clostridium spores to thrive. This is why lysozyme is often added during Gouda production to prevent the defect.
- Edam: Similar to Gouda, Edam has a semi-hard texture and ages in a low-oxygen environment, especially when waxed. If the cheese is not adequately salted or the milk is contaminated, late blowing can occur.
- Parmesan: Despite its lower moisture content, Parmesan is still susceptible to late blowing due to its extended aging period. Any contamination in the milk or during production can result in unwanted gas production months into ageing.
- Emmental and Swiss-style cheeses: Swiss-style cheeses like Emmental are naturally prone to gas formation due to their propionic acid bacteria, which create desirable holes (or “eyes”). However, contamination with Clostridium can lead to excessive or uneven gas formation, causing defects rather than the controlled eye development typical of these cheeses.
- Cheddar: While less common, Cheddar can also experience late blowing if hygiene during production or ageing conditions are inadequate. The defect is more likely in Cheddars aged for extended periods.
How to handle affected cheese
Cheese affected by late blowing is often unsafe to eat due to the presence of harmful bacteria, such as Clostridium tyrobutyricum. While it may not always cause illness, it is best to err on the side of caution and discard the affected cheese.
Instead of throwing the cheese in the trash, consider composting it. Here’s how:
- Break it into smaller pieces: This speeds up decomposition.
- Mix with other compostable materials: Combine with brown materials like leaves or cardboard to balance the nitrogen content.
- Monitor your compost pile: Avoid adding too much cheese to prevent an unpleasant smell or attracting pests.
By composting, you can reduce waste while giving back to the environment.
Learning from late blowing
Late blowing is frustrating, but it’s also a valuable learning opportunity for home cheesemakers. By carefully reviewing your process, you can identify what went wrong and make adjustments for future success. Here’s how you can turn a setback into a lesson:
1. Keep detailed records
Maintain a cheesemaking journal to document each step of the process, including:
- Milk source and type (e.g., raw, pasteurised).
- Cleaning and sanitation methods.
- Starter culture used and its quantity.
- Temperatures, pH levels, and pressing conditions.
- Salting method and amount.
Comparing records from successful and unsuccessful batches can help pinpoint potential causes.
2. Examine your milk source
Raw milk is more likely to contain Clostridium spores, especially if cows are fed silage. If you used raw milk, consider switching to pasteurised milk or ensuring stricter hygiene practices at the source.
3. Assess your sanitation
Late blowing often stems from contamination. Evaluate whether your cleaning methods were thorough enough. Sterilising all equipment and working in a clean environment can significantly reduce bacterial contamination.
4. Evaluate your starter culture
Weak or insufficient starter cultures might allow harmful bacteria to outcompete the beneficial ones. Next time, consider using a stronger culture or adjusting the quantity.
5. Analyse your ageing conditions
Improper humidity or temperature levels can contribute to late blowing. Double-check your ageing setup to ensure it aligns with the cheese type’s requirements.
6. Experiment with preventive additives
If you frequently make cheeses prone to late blowing, consider adding lysozyme or increasing salt levels to inhibit Clostridium spores.
Conclusion
Late blowing doesn’t have to be the end of your cheesemaking journey. By analysing your process and making informed changes, you’ll become a more skilled cheesemaker—and your next batch will be even better.
Mistakes are part of the learning curve, and every issue resolved is a step toward mastery.
Cheese lover. Scientist. Created a website and a Youtube channel about cheese science because he could not find answers to his questions online.
