California produces more than 30 almond varieties, but over 95% of the production comes from 11 major varieties. These California Almond varieties are grouped into three broad classifications — Nonpareil, California and Mission — for marketing purposes, based on distinguishing characteristics such as shape, size and “blanchability.”
The consistent quality of California Almonds is assured through research conducted by the Almond Board of California (ABC).
California Almonds (natural kernels) are marketed following USDA grade standards and/or sales contract specifications. Understanding the many characteristics of California Almonds will aid in their selection. The basic physical elements of almond quality are grade, variety, size and specification. Take “The Right Type for the Right Use” e-learning course to find out more about these characteristics.
Almond Composition and Natural Variability
Almonds have a quality nutrient profile, which includes important macronutrients like protein (6 grams per serving), monounsaturated fatty acids (8.9 grams per serving) and are a good source of dietary fiber. They are also an excellence source of both the micronutrient, vitamin E and the mineral magnesium, and also provide 75mg per serving of calcium. Composition data for California Almonds are found in the USDA National Nutrient Database. The USDA nutrient data sets, available for natural almonds, almond forms and roasted almonds, represent a comprehensive sampling of California-grown almonds. For natural almonds, the USDA nutrient values are averages based on more than 70 samples of nine major almond varieties grown in California over several years.
Current research shows that there are no major differences in nutrient composition among the major California Almond varieties. Nutrient contents can vary from sample to sample, even within a variety, because almonds are natural products. In general, the growing conditions (region, crop year and production factors) have a greater effect on nutrient composition than does the almond variety.
A study published in the Journal of Food Composition and Analysis compared the nutrient profiles of seven major almond varieties (Butte, Carmel, Fritz, Mission, Monterey, Nonpareil and Sonora). Almond samples were collected over three separate harvest years and from orchards in the north, central and south growing regions in California. Comprehensive analysis of macronutrients, micronutrients and phytosterols in the almond samples was carried out by accredited laboratories. The study found that these California Almond varieties had very similar macronutrient and micronutrient profiles. For example, the content of total fat and monounsaturated fatty acids was the same in all the varieties.
Almond composition. Almond Board of California, 2013.
Natural variability in the nutrient composition of California-grown almonds, ABC publication overview, September 2013.
Sweet and Bitter Almonds
In California, all almond trees growing in commercial orchards produce “sweet” varieties of almonds. The sweet or bitter flavor of an almond variety depends on the genetics of the parent tree in the orchard.
Almonds can be characterized by three flavor phenotypes: sweet (non-bitter), slightly bitter (or semi-bitter) and bitter. In general, a naturally occurring compound known as amygdalin is responsible for bitterness in almonds. Amygdalin is found in almond kernels and in the seeds of stone fruits like apricots. Bitter almonds contain high levels of amygdalin (3–5%), whereas only trace levels are found in almonds from sweet varieties (<0.05% amygdalin) and from slightly bitter varieties (<0.2% amygdalin). Bitter almonds are used mainly in the production of almond pastes and almond-flavored extracts.
Amygdalin breaks down to release hydrogen cyanide as well as sugars (glucose) and benzaldehyde. Hydrogen cyanide and benzaldehyde have similar aromas and are responsible for the bitter taste in almond kernels. Benzaldehyde, which is nontoxic, is extracted from bitter almonds, and is an important flavoring substance also known as “oil of almond” or almond essence.
To better categorize the flavor of sweet and slightly bitter almond varieties, it is important to be able to accurately measure the amount of amygdalin present. Until recently, very little information was available on the differences in trace amygdalin levels among the commercial almond varieties grown in California.
In a study conducted at the University of California, Davis, researchers developed a highly sensitive method to analyze for amygdalin levels in almonds. They used this method to compare the amygdalin levels in 10 commercial varieties of California almonds (sweet), and found that some varieties (e.g., Fritz and Aldrich) had slightly higher amygdalin levels. More research needs to be conducted on almonds harvested in different years to find out whether amygdalin levels in these varieties are consistently higher.
Quantification of amygdalin in non-bitter, semi-bitter and bitter almonds, ABC publication overview, July 2014.
Quantification of amygdalin in non-bitter, semi-bitter and bitter almonds (Prunus dulcis) by UHPLC-(ESI)QqQ MS/MS. Journal of Agricultural and Food Chemistry, 2013, 61(32):7754–7759.
The sensory characteristics of almonds can be described by an array of attributes. Distinctive texture attributes can include roughness, crunchiness, hardness, particulate mass, cohesiveness and adhesiveness, and be crispy and chewy. Typical almond aroma/flavor attributes can include overall intensity, fruity, marzipan (benzaldehyde), dark chocolate, nutty, woody, toasty and earthy.
A sensory lexicon is like a vocabulary of terms that can be used to describe and document the attributes of a product. In very simple terms, texture is evaluated for the almond surface, the various chewing stages, and the residual attributes after chewing. Aroma is evaluated by smelling the almonds before chewing. Flavor is evaluated as the in-mouth flavor impact as the nuts are chewed.
In a study at the University of Minnesota, researchers evaluated the sensory texture attributes of five types of almond forms (natural whole, dry-roasted whole, blanched whole, blanched slivered and natural sliced) at different moisture levels. Some of their findings about almond texture are listed below.
Natural raw whole almonds are high in crunchiness, hardness and cohesiveness while dry-roasted almonds are generally harder, crispier, crunchier and produce more loose particles. Natural almonds are harder, crisper and crunchier than blanched almonds. Compared with whole almonds, sliced and slivered almonds have less hardness, crunchiness, cohesiveness and tooth packing, and require fewer chews and swallows to consume. Compared with slivered almonds, sliced almonds are more powdery and have more surface roughness and loose particles, as well as less hardness, moistness, and cohesiveness of mass and fatty film. Sliced almonds broke into fewer pieces and required fewer chews and swallows to consume than did slivered almonds.
Almond texture is closely correlated with moisture. Sensory testing of texture showed that as moisture increases, moistness of mass and cohesiveness of mass increase. Crispness, hardness, crunchiness, persistence of crunch and particulate mass decrease with increasing moisture content. Consumers like crispness, crunchiness and persistence of crunch.
Texture can also be measured with instruments by using compression or bending tests. Read more about texture measurements and moisture.
Volatile compounds are responsible for the aroma and flavor attributes of foods. The almond lexicon study showed that the intensities of aroma/flavor attributes in raw almonds are relatively low, ranging between 0 and 5, which is indicative of mild-flavored products. The major California Almond varieties evaluated show a range of inherent variability in aroma/flavor attributes. This variability within an almond variety also may be influenced by crop years and growing regions.
A wide range of volatile compounds exists in raw, aged and roasted almonds. But the dominant flavor compound in raw almonds is benzaldehyde. Other volatile compounds in raw almonds include short-chain branched alcohols, aldehydes and ketones. Benzaldehyde is a breakdown compound released from the hydrolysis of amygdalin, a compound responsible for bitterness in almonds. California Almonds are sweet varieties that contain only trace amounts of amygdalin. Roasting diminishes the benzaldehyde intensity, which then may not be perceivable from sensory evaluation.
Flavor volatiles in roasted almonds are dominated by volatiles such as pyrazines and branched aldehydes and ketones generated during the browning reaction (also known as the Maillard reaction). The degree of roasting dictates the flavor intensity of roasted almonds.
Researchers at the University of California, Davis, have evaluated the volatile compounds in raw and roasted almonds.
Development of an almond lexicon to assess the sensory properties of almond varieties. Civille, G.V., K. Lapsley, G. Huang, S. Yada, J. Seltsam. Journal of Sensory Studies, 2010, 25(1):146–162.
Impact of almond form and moisture content on texture attributes and acceptability, ABC publication overview, July 2014.
Impact of almond form and moisture content on texture attributes and acceptability. Vickers, Z., A. Peck, T. Labuza, G. Huang. Journal of Food Science, 2014, 79(7):S1399–S1409.
Almond sensory evaluation procedure, Heymann, et al., July 2014.
Volatiles in raw and roasted almonds, ABC publication overview, July 2014.
HS-SPME GC/MS characterization of volatiles in raw and dry-roasted almonds (Prunus dulcis). Xiao, L., J. Lee, G. Zhang, S.E. Ebeler, N. Wickramasinghe, J. Seiber, A.E. Mitchell. Food Chemistry, 2014, 151:31–39.
Relative Humidity and Moisture
Almonds can pick up or lose moisture depending on their initial moisture content and the relative humidity (rH) of the surrounding environment — called moisture migration. Unwanted moisture migration in almonds may affect texture, microbial stability and the rate of various reactions that impact shelf life. When almonds pick up moisture (adsorption), they may lose some of their crunch, mold may start to grow, and lipid oxidation increases. Moisture loss (desorption) may lead to some desirable changes, such as more crunch, but at very low moisture lipid, oxidation also increases.
Moisture migration occurs until equilibrium within the system is reached; almonds in high-humidity environments will generally pick up moisture, especially at ambient and higher temperatures. Stopping moisture migration requires either a moisture-barrier package and/or reducing the humidity of the environment.
The effects of environmental rH on almond moisture levels are expressed by water sorption isotherms. As shown from almond isotherms, at a range from 20 to 65% rH, almonds will retain moisture levels from 3.0 to 6.0; at these levels, almonds are less prone to biological or chemical reactions. More ideal moisture levels for almonds are 3.0 to 5.0%, which can be achieved at environmental conditions of 20 to 55% rH. During storage, managing environmental humidity is a key to preserving almond quality. It is critical to maintain a steady environmental rH so the moisture levels in almonds will not fluctuate over storage.
Studies at the University of California, Davis, indicate that different varieties or sizes of whole almond kernels and pasteurized or unpasteurized almonds interact similarly with environmental rH, but roasted and blanched almonds interact differently.
Relative humidity fluctuation will affect almond moisture changes, which will impact texture quality. This online moisture and texture model demonstrates the effects of environmental rH on almond moisture content and the impact on texture properties.
To use the online moisture and texture model, click the image below.
Predictive modeling of textural quality of almonds during commercial storage and distribution. ABC research highlights, July 2014.
Moisture adsorption and thermodynamic properties of California-grown almonds (varieties: Nonpareil and Monterey). Taitano, L.Z., R.P. Singh. International Journal of Food Studies, 2012, 1:61–75.
Thermodynamic analysis of moisture adsorption isotherms of raw and blanched almonds. Taitano, L.Z., R.P. Singh, J.H. Lee, F. Kong. Journal of Food Process Engineering, 2012, 35:840–850.
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 in roasted almonds – ABC Technical Summary, July 2014.
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.
Oxidation and Rancidity
Lipid oxidation is a complex series of undesirable reactions that cause the breakdown of fats and oils. In oil-containing foods like almonds, the oxidation reactions lead to a loss of quality as the nuts develop “rancid” flavors and odors. During lipid oxidation, oxygen reacts spontaneously with the fatty acids in fats to form primary breakdown products (e.g., peroxides, conjugated dienes) and, as oxidation progresses, secondary products (e.g., volatile aldehydes, ketones) are formed that give rise to off-flavors and off-odors. Oxidation can be measured by testing for the presence or accumulation of one or more of these primary and secondary products. For example, almonds can be tested for peroxide value (PV) and free fatty acids (FFA).
High storage temperatures, increased moisture, light and some metals (e.g., iron) may promote lipid oxidation in almonds and reduce shelf life. Processing also makes almonds more susceptible to oxidation; blanching and cutting increase the surface area exposed to oxygen, and roasting changes the almond microstructure, which allows more oil within the cells to be exposed to oxygen.
Water activity (aw) level affects lipid oxidation rates; lipid oxidation is typically lowest when almond aw is ~0.25 to 0.35 (~3–4% moisture content), and increases above or below that aw range.
California almond shelf life: lipid deterioration during storage. Lin, X., et al. Journal of Food Science, 2012, 77(6):C583–C593.
Oil Migration and Chocolate Bloom
Roasted whole or cut almonds are used in chocolate as a center or inclusion. Almonds have a high oil content, and this characteristic is often assumed to be a potential concern for chocolate bloom, the quality defects that occur over time in chocolate products. The bloom may cause:
- Softening of chocolate;
- “Fat bloom” on chocolate surfaces; and/or
- Hardening of fillings.
These defects are generally the result of complex interactions involved in oil or fat migration. Oil migration has a critical impact on the quality and shelf life of chocolate products. Oil migration cannot be completely prevented but can be minimized through technical considerations in ingredient selection and chocolate-processing steps, such as proper tempering, as well as suitable handling and low-temperature (<68°F or <20°C) storage.
Recent studies of almond microstructure after roasting and almond oil migration in model confectionery systems by researchers at the University of California, Davis, are providing valuable insight into the processing requirements and behavior of almonds as ingredients in confectionery. In well-tempered chocolate products, light-roasted almonds didn’t show oil migration into chocolate media within a storage duration equivalent to a shelf life for commercial chocolate products. In a two-phase system with fillings made from ground almond products (butter, paste, crème), the researchers did not observe oil migration in the samples stored at or below 25°C (77°F); this indicates that the storage temperature is more critical than the filling composition for prevention of oil migration.
Oil migration in chocolate and almond product confectionery systems. Altan, A., D.M. Lavenson, M.J. McCarthy, K.L. McCarthy. Journal of Food Science, 2011, 76(6):E489–E494.
Oil migration in two-component confectionery systems. Lee, W.L., M.J. McCarthy, K.L. McCarthy. Journal of Food Science, 2010, 75(1):E83–E89.
Factors that Affect Shelf Life
Almonds are relatively low-moisture, high-oil-containing nuts with a long shelf life when properly handled. Almond quality and shelf life can be influenced by three general factors: the product characteristics, the environment during distribution and storage, and the package. These factors interact in many ways to influence almond quality and to impact shelf life. Because of these interactions, shelf-life guidance for almonds must specify the product and the storage conditions.
Storage Conditions and Handling Practices
Storage for all almond forms in cool and dry conditions (<50°F/<10°C and <65% relative humidity) is recommended. The optimal goal of the recommended storage conditions is to maintain <6% moisture content, which helps preserve shelf life. A cool temperature of <50°F/<10°C is optimal, but a higher temperature that does not stimulate insect activity may work as well to control moisture migration (and also minimize lipid oxidation). Almonds are a shelf-stable nut that can have more than two years of shelf life when stored at the recommended conditions.
Storage Study Findings
Maintaining almond quality during long-term storage in ambient conditions is challenging in emerging export markets, such as China, which can have widely varying temperatures and relative humidities, depending on the season and region. A long-term-storage study published in the Journal of Food Science evaluated the shelf-life quality of almonds — raw kernels, blanched kernels and blanched-sliced kernels — stored for at least 18 months in ambient and controlled (including abusive) conditions.
A shelf study conducted by U.S. Army Natick researchers proved that various almond forms (raw, roasted, blanched, sliced) can have a three-year shelf life when they are packed in optimal packages (tri-laminated foil pouches under vacuum).
Almond shelf life factors, ABC Technical Summary, July 2014.
Long-term storage study of raw and blanched almonds, ABC research highlight, October 2012.
California almond shelf life: lipid deterioration during storage. Lin, X., et al. Journal of Food Science, 2012, 77(6):C583–C593.
Packaging is an important factor in almond quality and shelf life. The package can provide physical protection and, when needed, a barrier to moisture and/or oxygen and odors. Roasted almonds have very different packaging requirements than in-shell almonds.
Almonds are delivered to the handler for sizing, sorting and grading, and then stored in bins or other bulk containers under controlled conditions before being shipped or further processed.
For container shipments to overseas markets, in-shell almonds are generally packed in sacks. Naturally shelled almonds are packaged in cartons or fiber bulk bins, depending on the product and volume. Cut almond forms and roasted almonds require more protection against moisture and oxygen.
Cut almonds are generally packaged in cartons with a plastic liner or fiber bulk bins with a plastic liner — the plastic liner provides an important moisture barrier. Roasted almonds must be protected from oxygen (e.g., with nitrogen flushing and/or vacuum packaging). Roasted almonds processed in California are typically packaged in vacuum-packed foil bags and shipped in 25-pound (11.3-kg) cartons.