The expression "flat as a pancake" is a common simile used to describe something that is very flat or lacking in elevation. While some pancake recipes indeed produce fluffy and thick pancakes, the expression likely originated from traditional pancake recipes that resulted in thinner, flatter pancakes.
Before the modern leavening agents like baking powder became widely available, pancakes were often made using simpler ingredients like flour, eggs, milk, and maybe a bit of fat. Without leavening agents, these pancakes would not rise much during cooking and would have a flatter appearance.
Over time, pancake recipes evolved, and leavening agents like baking powder and baking soda were introduced, leading to the fluffy pancakes we commonly enjoy today. However, the expression "flat as a pancake" persisted in language, even though it may not accurately represent the pancakes most people encounter in modern times.
Language often retains idioms and expressions from earlier periods, even when their original context might not apply anymore. The phrase has likely become more about the imagery it evokes rather than the reality of pancakes people typically encounter today. As with many idioms, it's essential to understand their historical context to appreciate their meaning, even if it doesn't align precisely with current practices or situations.