The addition of roasted malt and/or roasted barley.
Actually the difference between an Ale and Lager is the yeast. And with the difference in the yeast comes a difference in fermentation time and temperature. Ale yeast can ferment a batch of beer in as little as three weeks to bottle and need at least 55-60 degrees. Lager yeast can take over 6 months to ferment a batch and like around 40 degrees.