Evaluation function of drinking ease from aluminum beverage bottles relative to optimum bottle opening diameter and beverage type

In recent years, aluminum beverage bottles having screw tops with opening diameters of 28 and 38 mm have been launched in the Japanese market in keeping with the modern-day drinking habits of consumers. Although Japanese consumers are familiar with such bottles, a majority of them feel that the 28 mm opening is too small and the 38 mm opening is too large. Therefore, we felt the need to develop a method for evaluating consumer feelings when they drink a beverage directly from the bottle opening. For this purpose, we propose an evaluation function of drinking ease that calculates the optimum opening diameter of the bottle. From results of our previous study, we know that there exists an ideal volume of beverage flowing into the mouth, at which consumers feel most comfortable while drinking directly from bottles. Therefore, we define the evaluation function of drinking ease in terms of the difference between the actual volume of fluid in the mouth and the expected ideal volume. If this difference is small, consumers probably feel comfortable while drinking the beverage. We consider a design variable, i.e., the opening diameter, and two state variables, i.e., the volume of beverage remaining in the bottle and the height of consumers, and construct the response surface of the evaluation function by using radial basis function networks. In addition, for investigating the influence of beverage type on the evaluation function, we select green tea and a carbonated beverage (Coke) as test beverages. Results of optimization of the proposed function show that when the opening diameters are 35.4 mm and 34.4 mm in the case of green tea and Coke, respectively, the actual volume of fluid in the mouth is closest to the ideal volume and the participants feel most comfortable. These results are in agreement with results of our previous study that an opening diameter of 33 mm is optimum for young Japanese adults. Thus, we confirm that the proposed function is accurate; it can be used to design bottle openings to suit consumers of various age groups and types of beverages.