What does the strength of the three English bitter styles often correlate with?

The strength of the three English bitter styles—Ordinary Bitter, Best Bitter, and Premium Bitter—correlates with Alcohol by Volume (ABV) because these styles are primarily differentiated by their alcohol content. As the strength increases from Ordinary Bitter to Premium Bitter, so does the alcohol level. This progression typically reflects a balance in the beer's flavor profile, where a higher ABV often accompanies richer malt characteristics and possibly increased hop bitterness to maintain harmony in taste.

In contrast, while there may be some correlation between color intensity and strength, it is not a defining characteristic of English bitters. Color intensity can vary independently of alcohol content based on the grain bill and brewing process. Similarly, carbonation level does not inherently indicate the strength of the beer, as carbonation can be adjusted regardless of the beer's alcohol content. Lastly, malt sweetness plays a role in the flavor balance of these beers, but it does not provide an accurate indication of strength compared to the measurable ABV. Thus, the connection between strength and ABV is the most significant in understanding these styles.