Final answer:
To determine if a glass with beer is 'beer clean', you can check its clarity by observing if there are any impurities or haze present.
Step-by-step explanation:
To tell if a glass with beer is 'beer clean', you can check its clarity. If the beer appears clear without any particles or cloudiness, it can be considered 'beer clean'. You can hold the glass towards the light and observe if there are any impurities or haze present.