What happens to beer when it is poured into a frozen glass?

When beer is poured into a frozen glass, it causes foaming due to the rapid cooling of the beer upon contact with the extremely cold surface. The cold glass lowers the temperature of the beer quickly, which can cause carbon dioxide to come out of solution more rapidly, leading to excessive foam or head.

The other options do not accurately reflect the effects of pouring beer into a frozen glass. For instance, while a cold glass does help keep beer cold, it doesn't maintain the ideal temperature for all beer styles, which often prefer a specific range rather than freezing extremes. Additionally, flavor enhancement and carbonation increase do not occur as a direct result of this practice; rather, they can be negatively impacted by excessive foaming and cooling. Therefore, the most accurate consequence of this action is indeed the foaming that occurs when beer is poured into a frozen glass.