Plant Foods for Human Nutrition 53: 305–311, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. Environmental variables affect the hard-to-cook phenomenon of cowpea (Vigna unguiculata) seed S.S. AROGBA and J.D. ABU Department of Food Science & Technology, The Federal Polytechnic, P.M.B.1037, Idah, Kogi State, Nigeria Received 30 July 1997; accepted in revised form 9 September 1998 Abstract. Changes in moisture content and cooking rate of cowpea (Vigna unguiculata) seeds which were sun-dried for 5 hours on cement, wood, or corrugated iron sheet surfaces and packaged for 6 months in jute or polythene bags were studied. Relationships and effects of interacting variables studied were examined using the contrast analysis technique. From day zero to about 2 months of storage, the sun-dried samples had significantly (p<0.01) lower moisture content and longer cooking times than the corresponding control samples. However, moisture-gain and cooking time increased progressively throughout the storage period for all samples studied. The relationship between these two variables, tested at p=0.01 using contrast analysis technique, was dependent on the choice of packaging material. Key words: Cookability, Cowpea, Legume, Moisture, Packaging, Sun-drying Introduction Grain legumes are widely cultivated in tropical countries due to favorable cli- matic conditions, and they serve as a cheaper alternative source of protein to those of animal protein in diets of many developing countries [1, 2]. Nigeria and India are typical examples of tropical developing countries. For use in meals, legumes are processed by fermentation [3–5], soaking [6, 7] and/or cooking [5, 8–10] techniques in order to remove or destroy available antinutrients [1, 5–11]. Treatments (such as storage conditions and soaking conditions), degree of maturity and variety affect the cooking time of a particular type of legume. Cooking times ranging from 41 to 135 min for thirteen fresh cowpea varieties [12], 38.5 min for seven diverse cowpea varieties [13], about 4 h for mature dry winged beans [9], and about 1.5 h for unsoaked soybeans [5] have been reported. Legume seeds generally are known to exhibit progressive ‘hardening’ from seed development through maturity to storage [9, 14–16], and hence the ‘hard- to-cook’ phenomenon. Several complex factors external and internal to the tissue could concurrently or sequentially be participating in events leading to