Which of the following factors is least likely to affect beer flavor?

The least likely factor to affect beer flavor is the current week's weather. While weather can influence outdoor drinking conditions and perhaps impact the sensory experience through factors like humidity or temperature outside, it does not directly alter the inherent flavor profile of the beer itself.

In contrast, the type of beer has a significant impact on flavor due to the ingredients and brewing processes involved; different styles come with distinct profiles. Serving temperature can enhance or mute flavors and aromas, as some characteristics of beer are more pronounced at certain temperatures. Glassware shape is also important, as it can influence how aromas are concentrated and how the beer interacts with the drinker’s palate. Each of these elements can directly alter the experience and perception of flavor in a beer, unlike the weather, which remains an external influence.