Cold Brew Coffee Mould Risks & Safe Brewing Tips (UK / London Guide)

Cold brew coffee has surged in global popularity thanks to its smooth taste, lower perceived acidity, and refreshing profile. But because cold brew is made without hot water, it brings unique microbial safety concerns that both home brewers and cafés need to understand. Unlike hot coffee brewing—where boiling water kills microbes—cold extraction happens at low temperature over many hours, which may create conditions where mould, bacteria, and other microorganisms can grow if precautions are not taken.

Why Cold Brew Can Be at Higher Risk of Mould & Bacterial Growth

1) No Heat Means Microbial Risk

Traditional hot coffee is brewed at high temperatures that eliminate most contaminants. Cold brew, on the other hand, is steeped in cold or chilled water (often around fridge temperatures or room temperature) for 12–24 hours, meaning it lacks the sanitising effect of heat. This prolonged exposure to water without heat can allow certain microorganisms—including bacteria, yeast, and moulds—to survive and multiply.

2) Mild Acidity Isn’t Enough

Coffee naturally has acidic properties, and hot brewing can extract a wider range of acids that help inhibit microbial growth. Cold brew’s lower extraction temperature often results in less acidity, which reduces this natural barrier to spoilage organisms.

3) Extended Exposure Time

Steeping coffee grounds for long periods creates a more hospitable environment for microbes. If brewing equipment, water, or grounds aren’t clean, pathogens like E. coli, Salmonella, and other spoilage organisms could grow—especially in poorly controlled environments.

What Types of Contaminants Are a Concern?

Here are some of the microorganisms that could pose risks in improperly prepared or stored cold brew:

• Bacteria such as E. coli and Salmonella

• Yeast that can lead to off-flavours and fermentation

• Moulds that produce mycotoxins—harmful chemical byproducts from fungi growth

• Other spoilage microbes that thrive in cool, moist environments

Both mould and bacteria aren’t common in cold brew when best practices are followed—but if contamination occurs, it can impact both safety and flavour.

How to Brew Cold Brew Coffee Safely

Whether you’re making cold brew at home or for a café in London or elsewhere in the UK, here are essential food-safety steps:

1) Start With Clean, Sanitised Equipment

Make sure all containers, filters, and tools are thoroughly cleaned and sanitised before use. Microbes can easily cling to brewing vessels and filters if not properly washed.

2) Use Fresh, High-Quality Water and Beans

Ensure your water is potable and free of contaminants, and store coffee beans in a cool, dry place to prevent pre-brew mould growth on the grounds.

3) Keep Cold Brew Cold

After brewing, cold brew should be refrigerated at or below 5 °C (41 °F). While refrigeration doesn’t eliminate microbes, it slows their growth significantly.

4) Brew for the Right Time

Avoid over-extended steeping times beyond what’s needed for flavour. Very long extraction at room temperature increases exposure risk. Manufacturers and experts recommend controlling steeping duration and temperature to balance flavour and safety.

5) Consume or Store Properly

Even properly made cold brew should be consumed within a safe window. For packaged or kegged cold brew in food service settings, strict shelf-life and hygiene protocols are essential to prevent spoilage and maintain quality.

Recognising Signs of Spoilage

Mould or bacterial growth can be identified if cold brew:

• Develops off-odours or musty smells

• Tastes sour or “off” rather than smooth

• Shows visible film or sediment that wasn’t initially present

• Produces unexpected gas or cloudiness

If any of these appear, it’s safer to discard the batch.

Cold Brew Safety Is Manageable

Cold brew doesn’t have to be risky. With proper sanitisation, controlled temperatures, and good brewing discipline, you can enjoy its smooth, refreshing character safely—whether you’re making a pitcher at home or serving cans in cafés across the UK. Focus on cleanliness, refrigeration, and efficient production protocols to minimise mould and microbe growt