how do i clean the inside of my mr coffee 12-cup? it's starting to smell weird

Diagnosis

The "weird" smell you are experiencing is typically a combination of two distinct issues: rancid coffee oils and calcium carbonate buildup. Coffee contains natural oils that cling to the internal heating element and the showerhead (the part that drips water onto the grounds). Over time, these oils oxidize and turn rancid, creating a bitter or "stale" odor. Simultaneously, if you use tap water, minerals like calcium and magnesium precipitate out of the water and form a hard, chalky scale inside the aluminum heating tube. This scale creates a porous surface where bacteria and mold can hide, further contributing to an unpleasant scent. You can confirm this by looking at the water reservoir or the showerhead for white, flaky deposits or by noticing that the machine is brewing slower than it did when new.

How to Fix It

To fully sanitize the internal water path and remove the odor, you must perform a deep descale and a flush. Follow these exact steps:

1. Empty the carafe and remove any old coffee grounds from the filter basket. Ensure the basket is completely empty to allow the cleaning solution to flow freely.
2. Fill the water reservoir to the 12-cup maximum line with a solution consisting of 50% distilled white vinegar and 50% cold filtered water. Do not use apple cider vinegar or cleaning chemicals, as these can leave a permanent scent or damage the internal seals.
3. Place a fresh paper filter in the basket to catch any large chunks of scale that may break loose during the process.
4. Press the "Brew" button to start a full cycle.
5. When the carafe is approximately half full, press the "Off" or "Pause" button. Leave the machine in this state for 30 to 45 minutes. This "soak phase" allows the acetic acid in the vinegar to break down the hardened calcium deposits inside the heating tube.
6. After the soak, resume the brew cycle until the entire reservoir is empty.
7. Discard the vinegar solution and the used filter.
8. Fill the reservoir to the 12-cup line with plain, cold water. Run a full brew cycle.
9. Repeat the plain water rinse a second time to ensure no vinegar scent remains in the internal tubing.

If That Didn't Work

• Deep Clean the Showerhead: The smell may be trapped in the spray head at the top of the machine. Remove the filter basket and use a damp microfiber cloth dipped in vinegar to scrub the small holes where water exits. If you see black mold, use a cotton swab dipped in isopropyl alcohol to sanitize the crevices.
• Carafe De-staining: The smell often lingers in the glass carafe rather than the machine. Fill the carafe with warm water and a tablespoon of baking soda. Use a bottle brush to scrub the bottom and sides, paying close attention to the rim where the lid seals.
• Commercial Descaler: If vinegar failed, the mineral buildup is likely too severe. Purchase a citric-acid-based commercial descaling powder. Dissolve the powder in water according to the package instructions and repeat the brew/soak/rinse cycle described above. Citric acid is more aggressive than acetic acid and can dissolve heavier scale.
• Check the Water Filter: If your specific model has a charcoal water filter insert in the reservoir, remove it. These filters can become saturated and begin to smell like sulfur or damp earth once they expire. Replace the filter cartridge or run the machine without it.

Heads Up

• Frequency: Descale your machine every 3 months if using tap water, or every 6 months if using filtered water, to prevent the "weird smell" from returning.
• Water Quality: Using distilled water prevents scale buildup but can sometimes lead to "air locks" in certain Mr. Coffee models because there are no minerals to trigger certain sensors; filtered water is the ideal balance.
• Avoid Soap: Never put soap inside the water reservoir. If soap gets into the internal tubing, it requires dozens of rinse cycles to remove and can leave a chemical taste in your coffee.
• Dry the Basket: After your final brew of the day, remove the filter basket and let it air dry. Keeping a damp basket inside the machine creates a breeding ground for mildew.