Natural almonds may be processed into different forms (blanched, roasted, sliced, slivered, diced or ground) for ingredient or snacking applications. These products receive heat and/or size reduction treatments. The heat treatments may initiate some chemical reactions in the almonds. Size reduction treatments will increase the amount of surface area exposed to air. Both treatments will have some impact on the shelf stability of the processed almond products. Cut and roasted almond forms will have a shorter shelf life than natural whole almonds. To preserve the shelf life of processed forms, special attention should be paid to processing parameters (e.g., temperature, time) and post-process handling. Roasting is a common process that has the greatest impact on quality.
Roasting is a heat process that is used to modify the texture, color and flavor of natural California Almonds. Roasted almonds have a crunchier texture, a browner color and a desirable roast-flavor profile. Almond kernels, with skin or blanched, can be roasted by hot air (dry roasting) or in hot oil, depending on your application needs. Dry-roasted almonds are typically used in chocolates, confectionary products, breakfast cereals and baked goods, and increasingly for snacking. Oil-roasted almonds are typically used in ice cream and for snacking. In-shell almonds can also be dry-roasted for snacking applications.
Almonds are commonly roasted at 265 to 320°F (~130 to 160°C). Roasting at the low to mid temperatures of 265 to 293°F (~130 to 145°C) helps to preserve the almond microstructure and maximize product shelf life. Various roasting temperature and time combinations can be utilized to obtain light-, medium- or dark-roasted almonds. In most cases, the same degree of roast (in terms of color development) can be achieved at different temperatures by adjusting the roasting time: Longer times are required at the lower roasting temperatures, and shorter times at the higher roasting temperatures. To choose optimal roasting processes for California Almonds, consider the desired color and flavor as well as the shelf life and quality aspects.
The critical requirements of a roasting process for almonds are:
Delivering uniform heat treatment;
Providing consistent quality in nut color, texture and flavor;
Preserving nut integrity, subcellular microstructure and appearance;
Cooling roasted nuts immediately after heat treatment; and
Packing roasted nuts promptly after cooling with high-barrier packaging to limit oxidation during storage.
Hot roasting of almonds. ABC Technical Summary, July 2014.
Acrylamide in Roasted Almonds
Acrylamide is a chemical that forms naturally in some carbohydrate-rich foods (e.g., potatoes, bakery products, cereals) during frying, roasting and baking. In foods, most acrylamide is formed through a reaction between the free amino acid asparagine and the reducing sugars glucose and fructose. This reaction occurs mainly during the heating of food above 250°F (~121°C) in low-moisture conditions and is part of the Maillard reaction (also known as non-enzymatic browning).
Acrylamide at concentrations found in some foods is a concern because the chemical is known to cause cancer in laboratory animals and also may be a human carcinogen.
Almonds contain free asparagine and reducing sugars, the precursors for acrylamide formation. Acrylamide is not found in raw almonds, but is found in roasted almonds. Many factors influence the acrylamide levels in roasted almonds; most importantly, the roasting conditions, but also almond composition, variety and maturity.
Since 2003, the Almond Board of California has funded numerous research projects investigating acrylamide levels in almonds. These projects have ranged from commercial product surveys, analyses of acrylamide precursors in various almond varieties, and studies on how roasting temperature and time, as well as storage after roasting, may influence acrylamide levels.
A study published in the Journal of Agricultural and Food Chemistry found that roasting at a temperature below 295°F (146°C) to achieve light- or medium-roasted product will minimize acrylamide formation in roasted almonds. The University of California researchers demonstrated that roast temperature has a much greater influence on the final acrylamide content than the process time.
Acrylamide formation in almonds (Prunus dulcis). Zhang, G., G. Huang, L. Xiao, J. Seiber, A.E. Mitchell. Journal of Agricultural and Food Chemistry, 2011, 59(15):8225–8232.