Here is an explanation of calorie burn (kilocalorie or "Calorie"), energy expended (kiloJoule or "kJ"), and how these are estimated for cycling.
How Accurate is that Calorie Reading? | TrainingPeaks
Read down to the end for an example. The author did a ride, and
- from his power meter his estimated calorie burn was 2678 Calories (using approximation that applying 1 kJ to the pedals burns 1 Calorie of stored body energy)
- from his heart rate his estimated burn was 1938 Calories
- from time and distance his estimated burn was 3648 Calories
The power meter-derived estimate is most accurate, the heart rate-derived estimate is less so, and the time and distance-derived estimate is not accurate at all.
I consulted a standard bike power calculator. To ride 20 mph in the drops (road bike, flat ground, no wind, no drafting, my size and weight) requires about 175 watts. Riding 20 mph like that for a solid hour is, for me,
very hard work. Doing the math, 175 watts for 1 hour is 630 kJ generated or 630 Calories burned. That is consistent with my rule of thumb stated above, which is
"My rule of thumb - 1 hour of hard riding (heartrate high, sweating hard, legs screaming) is about 600 cal."
(By the way, this is one reason I don't have a power meter - I don't want to be depressed at how little power output I can actually sustain.)
So, for the OP, I think you should be skeptical about if you are actually burning 1100 Calories on the ride you described. It might be right, but it might also be way overstated.