Is Your Cold Brew Coffee Making You Sick? Common Issues

Quick answer

• Cold brew coffee itself is generally safe to drink.
• “Sickness” from cold brew is usually due to contamination or improper brewing methods.
• Common culprits include using unclean equipment, old coffee grounds, or contaminated water.
• Over-consumption of caffeine can also lead to unpleasant symptoms mistaken for sickness.
• Mold growth is a significant risk if cold brew is not stored or cleaned properly.
• Always use fresh ingredients and maintain a clean brewing environment.

What this problem usually is (and is not)

• This guide addresses symptoms like stomach upset, nausea, or a general feeling of being unwell after drinking homemade cold brew.
• It’s important to distinguish between actual illness and common side effects of coffee consumption, such as jitters or digestive discomfort from acidity.
• We are not discussing the inherent dangers of caffeine overdose or allergic reactions to coffee beans.
• This article focuses on preventable issues related to the brewing process and storage of cold brew coffee.
• We will not cover issues related to pre-packaged or commercially produced cold brew, which have different quality control standards.
• The goal is to help you identify and fix common problems that might lead to a bad brewing experience, not to diagnose medical conditions.

Likely causes (triage list)

Water Quality and Contamination

• Stale or contaminated water: Using tap water that has been sitting out or is of poor quality can introduce bacteria. Check if your water tastes off or has a noticeable odor.
• Dirty water source: If you’re using a filtered pitcher, ensure the filter is changed regularly and the pitcher itself is clean.

Coffee Grounds and Beans

• Old or rancid coffee grounds: Coffee grounds, especially if exposed to air, can go stale and develop off-flavors or even mold. Smell your coffee grounds; they should have a fresh, pleasant aroma.
• Improper storage of beans: Storing whole beans or grounds in humid or warm conditions can lead to spoilage. Ensure beans are kept in an airtight container in a cool, dark place.

Filter and Basket Issues

• Dirty or reused filters: Using the same paper filter multiple times or not thoroughly cleaning reusable filters can harbor bacteria and mold. Visually inspect filters for any residue or discoloration.
• Contaminated brewing vessel: The container you use for steeping, whether it’s a jar or a dedicated cold brew maker, can become contaminated if not cleaned properly. Look for any visible residue or a musty smell.

Machine Setup and Maintenance

• Unclean brewing equipment: Any part of your cold brew setup that touches the coffee or water needs to be spotless. This includes carafes, filters, and any steeping vessels.
• Incomplete cleaning: Residue from previous brews can build up and become a breeding ground for bacteria. Look for buildup in crevices or around seals.

Scale and Cleaning Buildup

• Mineral deposits: Hard water can leave mineral deposits in your brewing equipment, which can harbor bacteria and affect taste. This is more common with machines that use heating elements, but can still affect cold brew components over time.

Fix it step-by-step (brew workflow)

1. Gather your clean equipment: Ensure your brewing vessel, filter, and any storage containers are thoroughly washed with soap and hot water, then rinsed and dried.

• What “good” looks like: All surfaces are free of visible residue, and there’s no lingering odor.
• Common mistake: Rinsing quickly without soap, leaving behind oils and microscopic particles. Always use soap and hot water for a proper clean.

2. Measure fresh, quality coffee beans: Use whole beans roasted within the last few weeks for the best flavor and to minimize spoilage risk.

• What “good” looks like: Beans have a fresh, aromatic scent.
• Common mistake: Using pre-ground coffee that’s been open for a long time or beans that smell stale. This can introduce off-flavors and potentially harmful microbes.

3. Grind the coffee beans: Grind your beans to a coarse consistency, similar to sea salt. This is crucial for cold brew.

• What “good” looks like: Evenly sized, coarse particles.
• Common mistake: Grinding too fine. This can lead to over-extraction, bitterness, and grounds making their way into your final brew, which can be difficult to strain properly.

4. Combine coffee and water: Place the coarse coffee grounds into your brewing vessel. Add cold, filtered water. A common ratio is 1:4 to 1:8 coffee to water by weight or volume (e.g., 1 cup grounds to 4 cups water).

• What “good” looks like: All coffee grounds are submerged in water.
• Common mistake: Not ensuring all grounds are wet. Dry spots can lead to uneven extraction and potential mold growth.

5. Steep at room temperature or in the refrigerator: Cover the vessel and let it steep for 12 to 24 hours. Longer steeping generally results in a stronger concentrate.

• What “good” looks like: The mixture is steeping undisturbed.
• Common mistake: Steeping for too short a time (under 12 hours) or too long (over 24 hours), which can result in weak or overly bitter coffee, respectively.

6. Strain the coffee concentrate: After steeping, carefully filter the coffee concentrate to remove all grounds. Use a fine-mesh sieve, cheesecloth, or a dedicated cold brew filter.

• What “good” looks like: A clear liquid with no visible coffee grounds.
• Common mistake: Not straining thoroughly. Even a small amount of residual grounds can spoil quickly and impart a bitter taste.

7. Dilute the concentrate: Cold brew concentrate is typically very strong. Dilute it with water or milk to your desired strength, usually a 1:1 or 1:2 ratio of concentrate to liquid.

• What “good” looks like: A smooth, palatable beverage.
• Common mistake: Drinking the concentrate undiluted. This can lead to excessive caffeine intake and a very bitter taste.

8. Store properly: Pour the diluted cold brew into an airtight container and refrigerate immediately.

• What “good” looks like: The container is sealed and stored in the cold.
• Common mistake: Leaving the brewed coffee at room temperature for extended periods. This is a prime environment for bacterial growth.

9. Clean immediately after use: Wash all brewing components thoroughly after each use.

• What “good” looks like: All parts are clean and dry, ready for the next brew.
• Common mistake: Letting equipment sit dirty. This allows oils and residues to harden, making cleaning more difficult and increasing contamination risk.

Prevent it next time

• Cleanliness is paramount: Wash all brewing equipment thoroughly with hot, soapy water after every single use.
• Descaling: If your cold brew maker has removable parts that might accumulate mineral deposits (especially if you use hard water), descale them periodically according to the manufacturer’s instructions.
• Fresh water only: Always use fresh, cold, filtered water for brewing. Do not use water that has been sitting out for extended periods.
• Quality beans, fresh grounds: Use high-quality coffee beans that have been recently roasted. Grind them just before brewing.
• Proper grind size: Ensure your grind is coarse. Too fine a grind can lead to over-extraction and difficulty in filtering.
• Airtight storage: Store coffee beans in an airtight container in a cool, dark place. Store brewed cold brew in a sealed container in the refrigerator.
• Consume promptly: Aim to consume your homemade cold brew within 7-10 days of brewing for optimal freshness and safety.
• Regular filter checks: If using a reusable filter, inspect it regularly for wear or signs of mold. Replace if necessary.
• Avoid cross-contamination: Keep your coffee brewing area clean and separate from other food preparation areas to prevent contamination.
• Mind your caffeine intake: Be aware of how much caffeine you are consuming, as excessive intake can cause symptoms like jitters, anxiety, and digestive upset.

Common mistakes (and what happens if you ignore them)

Mistake	What it causes	Fix
Using unclean brewing equipment	Bacterial growth, mold formation, off-flavors, potential for stomach upset.	Wash all parts with hot, soapy water after every use.
Using stale or old coffee grounds	Rancid flavors, dull taste, potential for mold.	Use freshly roasted beans and grind them just before brewing.
Grinding coffee too finely	Over-extraction, bitter taste, cloudy brew, grounds in final cup, difficult to filter.	Grind to a coarse, sea-salt consistency.
Not steeping long enough	Weak, watery coffee with underdeveloped flavor.	Steep for at least 12 hours.
Steeping for too long (over 24 hours)	Over-extraction, excessively bitter and astringent taste.	Limit steeping time to 12-24 hours.
Incomplete straining	Grounds in the final cup, faster spoilage, bitter taste.	Strain multiple times if necessary using a fine mesh sieve or cheesecloth.
Storing brewed cold brew at room temp	Rapid bacterial growth, spoilage, potential for mold and foodborne illness.	Refrigerate immediately in an airtight container.
Using tap water that has been sitting out	Introduction of bacteria and off-flavors.	Use fresh, filtered water for brewing.
Not diluting concentrate	Extreme bitterness, excessive caffeine intake, digestive discomfort.	Dilute the concentrate with water or milk to taste.
Reusing disposable filters	Contamination, reduced filtration efficiency, potential for mold.	Use a new disposable filter for each brew.
Not drying equipment thoroughly	Lingering moisture can encourage mold and bacterial growth.	Ensure all brewing components are completely dry before storing.
Over-consumption of caffeine	Jitters, anxiety, rapid heart rate, digestive issues, insomnia.	Be mindful of serving size and caffeine content; dilute appropriately.

Decision rules (simple if/then)

• If your cold brew tastes bitter and has sediment, then you likely didn’t strain it thoroughly enough because fine particles were left behind.
• If your cold brew has a musty or moldy smell, then your equipment was not cleaned properly or has been left wet, allowing mold to grow.
• If you experience stomach upset after drinking cold brew, then check your brewing ingredients and equipment for cleanliness; stale grounds or contaminated water are common culprits.
• If your cold brew is weak and watery, then you probably didn’t steep it for long enough, or your coffee-to-water ratio was too low.
• If your cold brew concentrate is too strong to drink, then you need to dilute it with water or milk because cold brew is typically brewed as a concentrate.
• If your cold brew tastes sour, then it may have been exposed to air for too long or was not stored properly after brewing, leading to oxidation or spoilage.
• If you feel jittery or have heart palpitations, then you may have consumed too much caffeine; consider diluting your next batch or reducing your serving size.
• If your cold brew develops a slimy texture, then it has likely been contaminated with bacteria and should be discarded immediately.
• If your cold brew has a metallic taste, then it could be due to the water quality or potentially the material of your brewing equipment if it’s not food-grade.
• If your cold brew is cloudy and thick, then your grind might have been too fine, or you didn’t filter it adequately, allowing too many coffee solids into the liquid.

FAQ

Q: Can drinking moldy cold brew make me sick?

A: Yes, consuming moldy food or beverages can lead to symptoms like nausea, vomiting, diarrhea, and allergic reactions. Always discard any cold brew that shows signs of mold or spoilage.

Q: Is it safe to drink cold brew that’s been in the fridge for a week?

A: Generally, yes, if stored properly in an airtight container. However, for the best flavor and to minimize spoilage risk, it’s recommended to consume it within 7-10 days.

Q: Why does my cold brew taste sour?

A: A sour taste can indicate spoilage, especially if the brew has been left out at room temperature for too long or was not stored properly. It can also sometimes be due to over-extraction if the grind is too fine and steeps for an extended period.

Q: Can I reuse paper filters for cold brew?

A: No, disposable paper filters are designed for single use. Reusing them can lead to contamination from residual coffee oils and grounds, and they won’t effectively filter subsequent brews.

Q: What’s the difference between cold brew concentrate and ready-to-drink cold brew?

A: Cold brew concentrate is a highly concentrated form of coffee that requires dilution with water or milk. Ready-to-drink cold brew is already diluted to a palatable strength.

Q: How often should I clean my cold brew maker?

A: It’s best to clean all parts of your cold brew maker thoroughly with soap and hot water after every use to prevent bacterial growth and off-flavors.

Q: Can cold brew upset my stomach more than hot coffee?

A: Some people find cold brew easier on their stomach because the cold brewing process extracts fewer acidic compounds. However, individual reactions vary, and excessive caffeine can still cause digestive issues.

Q: What are the signs that my cold brew has gone bad?

A: Signs include a sour or moldy smell, visible mold growth, a slimy texture, or an off-putting taste. If you notice any of these, discard the brew.

What this page does NOT cover (and where to go next)

• Specific medical diagnoses: This guide is for troubleshooting brewing issues, not for diagnosing illnesses. If you suspect a serious health issue, consult a medical professional.
• Commercial cold brew safety standards: This article focuses on home brewing. Commercial products have different testing and safety protocols.
• Advanced coffee science: For deeper dives into extraction theory or specific chemical compounds in coffee, explore resources on coffee chemistry and brewing science.
• Troubleshooting electrical coffee machines: If you have an electric cold brew maker with specific component failures, consult the manufacturer’s manual or customer support.
• Allergies to coffee: This guide does not address coffee allergies. If you suspect an allergy, seek medical advice.