Soil erosion due to annual cropping on highly erodible farmland is a major ecological concern in the wheat growing regions of Washington State. In response to requests from farmers, the winter wheat breeding program at Washington State University has been developing perennial wheat selected from crosses between wild wheatgrass species and commonly grown annual wheat cultivars. In 2005/06, we conducted field trials of the most promising perennial wheat breeding lines derived from interspecific crosses between tall wheatgrass (Thinopyrum elongatum) and bread wheat (Triticum aestivum). Thirty-one perennial breeding lines and two annual winter wheat cultivars were evaluated for nutritional value in the form of grain mineral concentration, multiple baking and milling quality traits, and ease of grain threshability. The objective of this study was to identify the strengths and weaknesses of these post-harvest traits in the perennial wheat lines derived from these interspecific crosses. Mineral nutrient concentrations in the perennial lines were 44, 40, 24, 23, 32, 30 and 33% higher than the annual control cultivars for calcium, copper, iron, magnesium, manganese, phosphorus and zinc, respectively. The annual cultivars had a higher grain mineral content per unit area of land than the perennial lines, due primarily to the higher grain yields of the annual cultivars. Compared to the annual wheat cultivars, the perennial lines produced grain with smaller seed size, lower test weight and reduced flour yield, mix time and loaf volume. Protein content was 3.5–4.5% higher in the perennial lines than in the annual cultivars. The threshability index (TI) ranged from 0.63 to 0.89 in the perennials (μ=0.75); significantly lower than the mean TI of the annual cultivars (μ=0.97). The significant genotype×location interaction found for TI suggests that the variation in annual precipitation positively influenced some perennial lines to express greater threshability. In addition to transferring traits important to the perennial growth habit in wheat, the wild wheatgrass species also introduced beneficial characteristics (i.e. increased protein and mineral concentration) and deleterious traits (poor threshing grain and inferior baking qualities). This research gives researchers a platform from which to direct further research and selection in the development of perennial wheat.