"They have a really strong defence and it's not easy to penetrate it," coach Appiah told a news conference at the Castelao arena on Friday.
"Most of them have been together for a very long period. It's not going to be easy to penetrate, no matter who they put in their defence."
The Black Stars made a disappointing World Cup start, losing 2-1 to the United States and midfielder Andre Ayew said the Africans expected to perform better.
"We know the quality of the German defenders and we will see the quality of our strikers. It's going to be a tough one for both sides.
"We are the underdogs in this game. We're coming all out. "We want to do something great so we're going to fight as a team to get results."
Appiah, who has injury concerns over defender Daniel Opare, said Ghana's fighting spirit ensured they would not set out to frustrate Germany in the hope of snatching a draw.
"I actually don't believe in going out into a game and thinking let me go and get one point. Any game, my ambition is to go for a win," Appiah said.