Perfect for homemade mustard, stock and other reductions as well as the homemade bort spreads & pestos. TWIST Classic, straight-lined shape leads to many uses, the clear surface is also great for writing and labeling. The iconic twist-top closure lets them know if canning has been successfully accomplished by the inward curving surface. Ideally, after opening, you will hear the typical CLACK sound when the vacuum is released.