How do you know if your starter is not working in a focus?

To determine if your starter is not working in a focus, observe if it fails to rise or produce bubbles after several hours of feeding. Additionally, a sour or off smell, rather than a pleasant tangy aroma, can indicate that the starter is struggling. If the mixture appears watery or has developed an unusual color or mold, it may also signify that it’s not active. Lastly, if it doesn’t double in size within the expected timeframe after feeding, it’s likely not functioning properly.