E: Food Engineering & Physical Properties JFS E: Food Engineering and Physical Properties Optimization of Combined Microwave–Hot Air Roasting of Malt Based on Energy Consumption and Neo-Formed Contaminants Content S. AKKARACHANEEYAKORN, J.C. LAGUERRE, J. TATTIYAKUL, B. NEUGNOT, P. BOIVIN, F.J. MORALES, AND I. BIRLOUEZ-ARAGON ABSTRACT: To produce specialty malt, malts were roasted by combined microwave–hot air at various specific mi- crowave powers (SP = 2.5 to 3 W/g), microwave heating times (t mw = 3.3 to 3.5 min), oven temperatures (T oven = 180 to 220 ◦ C), and oven heating times (t oven = 60 to 150 min). The response variables, color, energy consumption by microwave (E mw ) and oven (E oven ), total energy consumption (E tot ), quantity of neo-formed contaminants (NFCs), which include hydroxymethylfurfural, furfural, furan, and acrylamide were determined. Response surface method- ology (RSM) was performed to analyze and predict the optimum conditions for the specialty malt. Production using combined microwave–hot air roasting process based on minimum energy consumption and level of NFCs. At 95% confident level, SP, T oven , and t oven were the most influencing effects with regard to E tot , whereas t mw did not affect E tot . T oven and t oven significantly affected malt color. Only T oven significantly influenced the NFCs content. The optimum parameters were: SP = 2.68 W/g for 3.44 min, T oven = 206 ◦ C for 136 min for coffee malt, SP = 2.5 W/g for 3.48 min, T oven = 214 ◦ C for 136 min for chocolate malt, and SP = 2.5 W/g for 3.48 min, T oven = 211 ◦ C for 150 min for black malt. Comparing with conventional process, combined microwave–hot air reduced E tot by approximately 40%, 26%, and 26% for coffee, chocolate, and black malts, respectively, and reduced HMF, furfural, furan, and acrylamide contents by 40%, 18%, 23%, and 95%, respectively, for black malt. Practical Application: An important goal for research institutions and the brewery industry is to produce colored malt by combining microwave and hot air roasting, while saving energy, getting desirable color, and avoiding the formation of carcinogenic and toxic neo-formed contaminants (NFCs). Therefore, one objective of this study was to compare energy consumption and content of NFCs during roasting of malt by hot air-only and combined microwave–hot air processes as well as to determine the effect of specific power, microwave processing time, oven temperature, and oven processing time during combined microwave–hot air roasting. Another objective was to pre- dict the optimum conditions for the production of coffee, chocolate, and black malts. Keywords: combined microwave–hot air, malt roasting, neo-formed contaminant, optimization, response sur- face methodology Introduction I n brewery industry, specialty malt or colored malt has been used to give particular colors and flavors to beers. Specialty malt or colored malt is malt which has coffee, chocolate, and black color (Hough and others 1971; Lewis and Young 2002; Briggs and oth- ers 2004). High temperature needs to be attained to get desirable color and flavor. During conventional roasting processes, mois- MS 20090877 Submitted 9/8/2009, Accepted 1/26/2010. Author Akkaracha- neeyakorn is with Dept. of Ago-Industrial Technology, Faculty of Applied Science, King Mongkut’s Univ. of Technology North Bangkok, 1518 Pibul- songkram Rd., Bangsue, Bangkok 10800, Thailand. Author Laguerre is with Dept. of Food Engineering, Inst. Polytechnique LaSalle Beauvais, Rue Pierre Waguet, BP 30313, 60026 BEAUVAIS Cedex, France and AgroParis- Tech, UMR 1145 G´ enie Industriel Alimentaire, F-91300 Massy, France. Author Tattiyakul is with Dept. of Food Technology, Faculty of Science, Chu- lalongkorn Univ., Payathai Rd., Patumwan, Bangkok 10330, Thailand. Au- thors Neugnot and Boivin are with French Inst. of Brewing and Malting, 7 Rue du Bois de la Champelle – BP267 – F-54512 Vandoeuvre Cedex, Nancy, France. Author Morales is with Consejo Superior de Investigaciones Cien- tificas (CSIC), Calle Serrano 177, Madrid 2800, Spain. Author Birlouez- Aragon is with AgroParisTech & SPECTRALYS Innovation, 102 bd Gaston Roussel, 93230 Romainville, France. Direct inquiries to author Laguerre (E-mail: jclaude.laguerre@lasalle-beauvais.fr). ture is initially removed off from the surface of the grain and wa- ter moves from the interior of the product to the dried surface through a diffusion process. This phenomenon is time- and energy- consuming. In a microwave drying system, the product heating is associated with a volumetric heat generation, which leads to higher internal temperature resulting in an increase in internal va- por pressure which helps to push liquid flow towards the surface, making it possible for higher drying rates (Prabhanjan and others 1995; Mujumdar 2000; Sharma and others 2000). In a conventional roaster, the temperature increase to 200 ◦ C in a malt bed needs sev- eral hours whereas microwave heating requires few minutes. There have been researches showing an improvement in the quality of fin- ish products such as apple, mushroom, carrot, garlic, potato, meat, and cookie dough when microwave is used in combination with other processes such as infrared heating, convective, and vacuum drying (Prabhanjan and others 1995; Funebo and Ohlsson 1998; Mujumdar 2000; Sharma and Prasad 2001). Combined microwave- conventional heating process can reduce surface moisture more efficiently when compare with microwave-only heating (Decareau 1985; Datta and Ni 2002). Combined microwave–hot air drying re- sulted in a reduction in the drying time to an extent of 80% to 90% C  2010 Institute of Food Technologists R  Vol. 75, Nr. 4, 2010—JOURNAL OF FOOD SCIENCE E201 doi: 10.1111/j.1750-3841.2010.01567.x Further reproduction without permission is prohibited