Aims: To study the accumulation of vegetative cells and endospores of Alicyclobacillus, as well as viable aerobic counts during the continuous production of apple juice concentrate. Methods and Results: Apples were processed for a continuous process running time of 108 h (processing rate 1 center dot 8-2 center dot 0 t h-1) without clean-in-place (CIP) procedures in-between different batches. Samples from single-strength apple juice, concentrate after evaporation (+/- 30 degrees Brix), the final product (concentrate pasteurized at 102-104 degrees C for 90 s) and condensate water (by-product of the juice concentration process) were collected every 12 h. From 12 to 84 h of processing, vegetative Alicyclobacillus counts in single-strength apple juice increased significantly (P < 0 center dot 05) from 1 to 3 center dot 15 log(10) CFU ml-1. Accumulation patterns of vegetative cells in apple concentrate and the final product were similar from 24 to 84 h of processing, with the respective counts increasing from 0 center dot 13 to 1 center dot 63 and 0 center dot 01 to 1 center dot 69 log(10) CFU ml-1. The highest Alicyclobacillus endospore counts in single-strength juice, concentrate and the final product was at 84 h of processing with 1 center dot 32, 1 center dot 59 and 1 center dot 64 log(10) CFU ml-1, respectively. Conclusions: Alicyclobacillus vegetative cells and endospores accumulate in fruit concentrates during a continuous process running time of 108 h. Significance and Impact of the Study: In conjunction with good manufacturing practices, fruit concentrate manufactures can minimize Alicyclobacillus accumulation in fruit concentrates by limiting the continuous process running time between clean-ups to under 84 h.