Increasing protein content is desirable in caramel, although the heating process during cooking sometimes leads to excessive protein aggregation, or "protein grain". Caramels formulated from 0% to 7% protein were cooked to 10% moisture, using either increased cooking rate or holding time at 88 degrees C. Protein aggregation was significantly enhanced at higher protein contents, increased cooking rates or shorter holding times at 88 degrees C. Increasing protein significantly decreased cold flow and produced harder, tougher caramels. Rapid cooking resulted in significantly harder, tougher and shorter caramels, with greater effects at higher protein content, while slower cooking produced softer, stretchier caramels. Protein aggregation may have been responsible for textural differences observed between cooking methods: caramels with smaller aggregates were significantly softer than those that had large aggregates. Extent of protein aggregation had no effect on cold flow. Tensile testing suggested that protein aggregates disrupt the continuous phase of caramels, shortening and toughening texture. (C) 2016 Published by Elsevier Ltd.