Labelled by captain Philipp Lahm on Friday as the best Germany side in at least the last six years, the team must prove their worth in their Group D opener against defence-minded Australia on Sunday.
"Philipp wanted to express his confidence and trust to his team-mates. We have great potential with this squad but now is the moment of truth," Bierhoff told reporters before the team boarded a plane bound for Durban.
"Yesterday's World Cup opener between South Africa and Mexico was the starting shot and now it gets serious."
Germany saw five key players drop out of the squad with injuries before travelling to South Africa, but coach Joachim Low refused to call up any other players, putting his trust in the country's youngest World Cup squad in 76 years.
Having breezed past Hungary and Bosnia in their last warm-up matches, Germany showed they were in good form but were hardly tested against the weaker sides.
With a backbone of players who won the European under 21 title last year, the current team has never played together on the big stage, has never had to come back from a goal down in a competitive match and has not experienced the atmosphere of a sold-out World Cup venue.
"We saw in our friendly match against Bosnia that a lot of the things worked well. The advantage is that many players know each other and have played together since the youth teams," said Bierhoff.
"But there is no time to find your groove. We have to peak against Australia."
Bierhoff also brushed aside comments by Australian players that 24-year-old Germany starting goalkeeper Manuel Neuer was the team's weak link.
With only five caps to his name, Neuer, who replaced injured Rene Adler, may be inexperienced but shows no signs of nerves, said the former Germany striker.
"We are convinced of his qualities because Manuel is a fantastic keeper. He is not nervous at all but very focused.
"He knows this is an important tournament but he has not lost his smile," said Bierhoff.
