The unsaturated nature of the anthocyanidin structure makes it susceptible to molecular oxygen. It has been known for many years that when grape juice is hot-filled into bottles, complete filling of the bottles will delay degradation of the color from purple to dull brown. Similar observations have been made with other anthocyanin-containing juices. The positive effect of oxygen removal on retention of anthocyanin color has been further demonstrated by processing anthocyanin-pigmented fruit juices under nitrogen or vacuum [26,131]. Also, the stability of pigments from Concord grape juice in a dry beverage is greatly enhanced when the product is packaged in a nitrogen atmosphere. Though little information exists relating
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to anthocyanin stability, stability was found to be greatest at
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values in the range of 0.63–0.79