Boiling proteins under reflux. The brown solution being heated contains proteins. They are being boiled in a flask attached to a reflux condenser (upper centre). The reflux condenser has cold water flowing around it, provided by pipes (orange). This rapidly cools any vapour that rises from the protein solution, causing it to condense and fall back into the flask. Heating proteins causes them to lose their folded structure (denature). When this is done at boiling point it causes irreversible damage to the molecule.