ProductManual espresso maker ECC221.BThe coffee has an acid taste
Manual espresso maker ECC221.B

The coffee has an acid taste

Try this solution

After descaling, rinse the appliance as described in descaling guide

Potential cause:
Inadequate rinsing after descaling.

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De'Longhi Coffee Machine Descaler EcoDecalk 500ml Best Value Pack (delonghi.com)