One by one: The β-barrel-forming outer-membrane protein G (OmpG) from E. coli can be folded into the native lipid membrane by using single-molecule force spectroscopy. Surprisingly, single β strands do not refold individually but as β hairpins that refold consecutively until the entire β-barrel membrane protein is refolded (see picture). This mechanism significantly advances the understanding of current folding models of β-barrel proteins.