Almonds Pasteurization

Introduction:In September 2007, the USDA began requiring that all almonds grown in California and sold as raw in the United States be sanitized via pasteurization. This decision was prompted by two outbreaks of Salmonella in the early 2000s that were traced back to conventional almond farms in California. In response to these outbreaks, the Almond Board of California a quasi-governmental marketing agency representing California's almond growers decided that the best way to ensure the safety and reputation of its product was to henceforth require the pasteurization of all almonds grown in the Golden State, which amount to virtually all almonds sold in this country.

Almonds Pasteurization:There are several pasteurization treatment processes that reduce the level of potential contamination in almonds without diminishing the products quality, nutritional value or sensory qualities (taste and crunch). They have all been evaluated and approved by the Food and Drug Administration (FDA).The processes are: Blanching Oil roasting Dry roasting Steam processing/Hot air roasting Propylene oxide (PPO)Blanching:Blanching is a thermal process that is used by almond processors to remove almond skins. Scalding and drying are the steps in which almonds are exposed to heat, and scalding is the step of interest for validation.Flow chart:

Bin Dump or Holding Tank

Transferring Conveyor or Elevator

Pre-wet Tank or Brine Floater

ScalderSkin Aspirator

Skin Collector

Blancher Roller Chamber

Water Rinse Table

Transferring Conveyor or Elevator

DryingLoosen skin or piece separator

Cooling Deck

Transferring Conveyor or Elevator

Electronic SorterScalding is a continuous process that is carried out in a circular tube in which hot water or steam-injected water is used to soak almond kernels. Almond kernels are directly exposed to hot water only in the section from point A to point B. The duration of the exposure to hot water is controlled by the scalder speed dial. The water temperature in the scalder is controlled by a control panel with a thermocouple attached to the near-end of the immersion section (point B). Some scalders may be equipped with a temperature recording device to monitor the water temperature. Though the scalded kernels from point B to the exit may be hot and carry residual hot water, this is not considered part of the controlled thermal treatment. The temperature of almond kernels at the input and loading speed (throughput) may make the water temperature fluctuate.

Scalding illustrationThe scalded almond kernels pass through a series of rubber rollers in the blanching chamber in which the loosened skins are removed. The blanched kernels, with some free skins, drop to a shaking table where the free skins are aspirated away while the debris is rinsed off the kernels by spraying water. The blanching chamber and water rinsing table operate in a wet and warm environment. Some thermal stable or thermophilic bacteria that survive the scalding step can populate to increase microbial count for finished blanched products. This also applies to the transference conveyor or elevator buckets between the water rinsing table and dryer. Proper and frequent sanitation is key to the reduction and control of microbial growth in these areas.The same scalding parameters (time and temperature) can be used for different blanched products (whole, whole and broken, pieces, cutting inputs, etc.) while the same blanched product may utilize different scalding time and temperature parameters if the almonds are different varieties or have different moisture levels. Therefore, there may be many sets of scalding time and temperature parameters utilized by a blanching line.Type of ProcessingMin. TemperatureMin. Time for 5-log reductionTemperatureD-value(min.)z-value

Hot Water Blanching82.2C(180F)3.09

82.2C (180F)0.6230.0C(53.0F)

85C (185.0F)2.49

87.8C(190.0F)2.0

Pasteurization was achieved after a minimum of 2 minutes with a minimum water temperature of 190F at the coldest point in the blancher. The FDA has determined that, when operating under specified parameters for 5-log reduction, blanched almonds may be labeled as pasteurized.

Oil roasting:Oil roasting is one of the processes that are used by the industry to obtain crunchy and roasted flavor almond products. A commercial oil roast is often carried out in a pre-heated oil tank equipped with a continuous conveyor that carries almond kernels through the tank where the kernels are roasted while they are submerged in the hot oil. Since some of the oil is absorbed or carried away by almond kernels, the oil level is maintained by continuous circulation from an oil reservoir.The duration of the roast is controlled by the conveyor speed dial setting, and the oil temperature is controlled by a thermocouple submerged in the oil tank. The temperature setting for the oil tank and temperature uniformity of hot oil may be affected by the length of the tank, temperature of almonds introduced into the oil, loading capacity (throughput), etc. Oil roasting is often combined with salting and flavoring processes.In general, oil roasting is a much faster process than dry (hot air) roasting. Oil roasting parameters (oil temperature and time) are dictated by the desired degree of roast, throughput rate, initial temperature and initial moisture level of the almonds, volume of the heated oil, etc. The temperatures commonly used in commercial oil roast processes are 280 to 350F. Normally under these temperatures, 3 to 15 minutes of roasting time is needed to achieve crunchy and crispy oil-roasted almond products.In almost all instances, common commercial oil roasting is carried out at temperatures higher than 260F and for longer than 2.0 minutes. Thus, the heat exposure under these conditions is much greater than the minimum process of 2.0 minutes exposed to hot oil at or above 260F to achieve a 5-log reduction. However, if there is a need for a shorter process, the minimum process parameters for a 4-log reduction are 1.6 minutes at a minimum oil temperature of 260F.Pasteurization was achieved after a minimum of 2 minutes at a minimum oil temperature of 260F at the coldest point in the oil roaster. The FDA has determined that, when operating under specified parameters for 5-log reduction, oil roasted almonds may be labeled as pasteurized.Minimum TemperatureMinimum TimeMinimum Time

127C (260F)4-log kill5-log kill

127C (260F)1.6 min2.0 min

Dry roasting:Dry (hot air) roasting is a thermal process used by the almond industry. A dry roast can be achieved via a continuous conveyor roaster or rotary roaster. The continuous conveyor roaster can be single-stage or have multiple-stages with a variety of temperature controls. Common temperatures used for hot air roasting range from 265F to 310F. At the lower temperature, it may take 40-55 minutes to obtain a light to medium roasted product while at the higher temperature, it may take 10-15 minutes to obtain a light to medium roasted product.In general, time/temperature combinations vary with the desired degree of roast, product bed depth and speed (or throughput), initial moisture levels and initial temperatures of almonds, hot air dynamics and/or air velocity of a roaster, etc. Equipment design varies from one brand to another, and from one style to another. This consequently will impact heat transfer and microbial reduction obtained during roasting. For example, in a single-stage conveyor roaster, the hot air comes through the conveyor from below. Almond kernels close to the conveyor would receive more heat exposure than the kernels on the top of the bed of product. For some two-stage roasters, hot air blows from the bottom of the first zone then from the top of the second zone, therefore the kernels at the bottom, middle and top would not receive the same heat exposure. The individual kernels from a rotary roaster generally receive more uniform heat exposure.The degree of roasting is dictated by customer specifications, and it is generally categorized as light, medium and dark roast, defined by color and moisture levels of a roasted product. Typically, light-roasted products require less heat treatment than dark-roasted product. However, the color and moisture or degree of roast of the finished product does not necessarily correlate with the amount of heat exposure the products received. In other words, the same degree of roast can be achieved from different heat exposures (i.e. time/temperature combinations). Sometimes, a set of roasting parameters will be established for certain product specifications. The roasting parameters may be altered to meet the specification if the initial moisture and initial temperature of the almonds are changed. Thus, there may be many parameter settings for each roasting line or even many versions of parameters for a single product specification.

Continuous conveyor roasterDry roasting processes may achieve a 4-log reduction under certain parameters; however, this is equipment/process specific. A variety of thermal and non-thermal treatments are available to the industry which meet the pathogen-reduction criteria for almonds. Studies to date indicate that processes appropriate for raw almonds have not resulted in any significant or meaningful impact on raw almond characteristics (i.e., freshness, surface integrity, color, texture); a more comprehensive sensory and quality evaluation of pasteurized almonds is currently underway. Thermal treatments meet organic standards.Hot air roasting/Steam processing:Hot air (dry) roasting is a thermal process suitable for almonds. Roasting changes the flavor profile of the almonds and results in a brown color and a crunchy texture. Light-, medium-, or dark-roasted products are achieved with specific temperature-time roasting treatments. Flavor composition and intensity depend on the roasting conditions. Hot air roasting temperatures typically range from ~130 to 154C (~265 to 310F). Almonds are rich in unsaturated fatty acids, but the high degree of unsaturation makes almond oil susceptible to oxidation during processing and storage. Oxidative reactions degrade the quality of roasted almonds and limit their shelf life. The use of lower hot air roasting temperatures helps to preserve the almond microstructure and maximizes shelf life. Hot air roasting for almonds can be optimized by applying a two-step roasting process. The first step uses an intermediate temperature to stabilize the nut microstructure, and the second step uses a higher temperature to generate the desired flavor and color. This summary highlights the latest research on hot air roasting technology and proposes optimal almond processing and handling.To achieve high quality roasted almonds, a roasting process must meet the following requirements: Heat treatment must be uniform. Heat treatment must provide consistent quality in color, flavor, and texture. Roasting equipment must transfer only minimal mechanical energy to the nuts to preserve integrity and appearance.The development of roasting equipment and processes has been driven mainly by technical innovation. A wide range of hot air roasting systems is available, including continuous roasters (single belt convection roasters, vertical continuous roasters, continuous drum roasters, etc.) and batch roasters (semi-fluidizing batch roaster, drum roasters, ball roasters, etc.).Continuous roasters are usually limited in terms of roasting temperatures and times, but may be preferable if variations in product and roasting degree are of minor importance. Batch roasters are very versatile and are often able to achieve a wide range of roasting degrees and product qualities. With modern control systems, batch processes can be run in a quasi-continuous manner, eliminating the operational differences between batch and continuous systems.Uniform heat transfer:Roasting requires a sufficiently high energy transfer rate. To avoid temperature differences that lead to color differences among the nuts, it is essential to either mix the nuts, as in rotary drum or ball roasters, or to distribute the energy uniformly through the nuts. However, mechanical action in rotary roasters may impair the surface structure of almonds, causing release of oil.Cooling:Cooling must be considered part of the roasting process. A rapid air-cooling process is essential to stop the roasting reactions after processing is complete. The roasted product must be cooled to below 2530C (7786F) to limit oxidation during storage. The product should not be packed and sealed if the product temperature is above 30C (86F) because moisture may condense on the inner surface of the package.Two-step hot air roasting process:Hot air roasting for almonds can be optimized by applying a two-step roasting process. The first step uses an intermediate temperature to stabilize the nut microstructure, and the second step uses a higher temperature to generate the desired flavor and color. In the two-step roasting process, microstructure degradation during roasting is reduced, which in turn leads to increased oxidative stability.The two-step roasting process is achieved with a semi-fluidizing hot air batch roaster. More than 100,000 tons of nuts can be processed per year with this two-step roasting system.Improved oxidative stability by the two-step roasting process compared to traditional industrial hot air roasting processes has been clearly demonstrated for almonds, hazelnuts, and peanuts in many industrial scale trials comparing different nut types and varieties, roasting processes, and roasting degrees. In all trials investigated, nuts roasted with the two-step process exhibited superior shelf stability compared to nuts roasted with a traditional hot air process.Propylene oxide (PPO): Pasteurization now include chemicalsFDA has loosely changed the definition of pasteurization to mean anything that destroys bacteria (good and bad) in the food, and deemed safe so long as the smell, taste and texture is not destroyed. To avoid having to remove the label raw when selling almonds to consumers, the Almond Board of California (ABC), which oversees virtually all almonds grown in the U.S. and Canada decided to use another form of pasteurization. Instead of pasteurization through heat, they will be using propylene oxide (PPO) in a process referred to by the FDA as terminal gas sterilization. PPO is a highly explosive flammable, so nasty that it was banned by both the National Hot Rod and American Motorcycle Racing Associations.Propylene oxide (PPO) is a registered fumigant in the US for reduction of bacteria, yeasts, and mold on raw nut meats, etc., and PPO fumigation has been used by the nut industry for insect and microbial control for decades. Recently, Almonds board of California (ABC) funded research projects demonstrated that PPO fumigation is an effective treatment for almond pasteurization. Process steps:1. Pre-warm product to at least 86F (30C) at the coldest point in the container. The product temperature should not exceed 105F (40C) during this step due to product quality concerns. The pre-warm temperature area can be in the range of 100 - 120F to achieve the 86F (30C) minimum product temperature. 2. Measure product temperature from the center of every bin or pallet to assure that the product achieves a minimum temperature of 86F (30C).3. Pre-heat the PPO chamber to 117-125F (47-51C). 4. Load the conditioned product into the pre-heated PPO chamber and start the cycle. 5. Maintain a chamber temperature of 117F to a maximum of 125F (47-51C).6. Apply a vacuum until the chamber reaches a minimum of 27 Hg. 7. Turn on PPO vaporizer to achieve a temperature of at least 140F (60C), but not in excess of 160F (71C). 8. Inject a sufficient amount of PPO through the vaporizer to assure that PPO vapor in the chamber reaches at least 0.5 oz. PPO/ ft3. (The absolute amount of PPO will depend upon the chamber size.) The vacuum in the chamber will decrease slightly upon addition of the PPO. 9. Inject an inert gas to decrease chamber vacuum to 5-6 Hg at completion of the injection to assure adequate amount of inert gas added. The pressure may fluctuate a bit during the sterilization process. 10. Treat product for 4 hours. (The pasteurization time begins after completion of inert gas injection.)11. After 4 hours of exposure, increase the vacuum to 27-28 Hg. 12. Complete the aeration cycle by saturating the chamber with an inert gas or air until atmospheric pressure is reached.13. Repeat aeration cycles a minimum of 4 times as required by the label, but not more than 14 times, to assure a safe PPO concentration in the chamber for worker access. The number of cycles varies with chamber size and it should allow product right out of the chamber to contain more than 400 ppm of PPO residue.14. After completion of aeration cycles, transfer the product to a room for post-ventilation treatment. The temperature recommended for post-ventilation is 100-110F (38-43C) for at least two days or at ambient temperature above 59F (15C) for five days. A higher temperature speeds up dissipation of PPO and shortens the holding time to achieve a PPO residue of 300 ppm or less in the product.15. Release the product when PPO residue is below 300 ppm.16. Record all measurements and document all recordings for each PPO pasteurization treatment. 17. Good manufacturing practices must be followed to assure that recontamination of the treated almonds does not occur.PPO Pasteurization Operating Parameters:Parameters Operational Level

Initial product temperatureNot less than 86F (30C)

Chamber temperature at start and during sterilization117-125F(47-51C)

Chamber vacuum before PPO injectionAt least 27Hg vacuum

PPO vaporizer temperature140 -160F (60-71C)

PPO concentrationNot less than 0.5oz PPO/ft3

Chamber vacuum at completion of inert gas injection5- 6 inch Hg vacuum

Duration of pasteurization4 hours

Aeration cyclesNot 14

Post ventilation100-110F (38-43C) for 2 days or above 59F (15C) for 5 days.

The parameters detailed here apply to almond kernels as well as in-shell almonds to achieve a minimum 5 log reduction of Salmonella.References:Different types of nut roasters link: http://www.nutroastingmachine.com/new_machines.htmhttp://www.gracepackagingmachine.com/public_html/roaster_&_flavor_rotary_drum.phphttp://ucfoodsafety.ucdavis.edu/files/26474.pdfhttp://www.almonds.com/processors/processing-safe-product#pasteurizationhttps://books.google.com/books?id=wlpEAgAAQBAJ&pg=PA37&lpg=PA37&dq=PPO+Standard+Operating+Procedure+for+almonds&source=bl&ots=MJxioLlPtp&sig=7KC_PbpyOw8hfEyZYu34BzZE6dU&hl=en&sa=X&ei=Vvr5VOXmJ8H3yQTB4YBo&ved=0CE0Q6AEwCA#v=onepage&q=PPO%20Standard%20Operating%20Procedure%20for%20almonds&f=falsehttp://www.healthbeyondhype.com/info/pasteurized-almonds-what-you-need-to-knowhttp://www.almonds.com/sites/default/files/content/Technical%20%20Information%20Kit.pdfhttp://www.ilovepecans.org/wp-content/uploads/2013/06/PasteurizationProtocolforPecanShellers.pdf