When do pistachios split

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Charter could you please One reason, obviously, is that we like the taste. But pistachios also have developed a reputation as a guilt-free snack with plenty of nutritional benefits, rich in unsaturated fats, fiber and antioxidants. Research suggests that pistachios could help to reduce hypertension and promote development of beneficial gut microbes. They're even gaining credibility as a tool for weight loss — partly because, like other nuts, they give a person a full feeling, and partly because the extra work needed to crack their shells and extract them helps to slow down consumption.

In one study , subjects who snacked on pistachios they had to remove from their shells consumed 41 percent fewer calories than those who were given pistachios with the shells already removed.

But that leads to another question. Why are pistachios one of the few nuts commonly sold to consumers with their shells still attached?

To roast and salt nuts like walnuts or cashews, producers need to remove the protective shell. But the reason that's not so for pistachios? Between 70 and 90 percent of pistachios develop a natural split in their shells during the growing process, says University of California, Davis pistachio expert Louise Ferguson , co-author of the " Pistachio Production Manual. Only the minority of nuts that don't split on their own are run through industrial shell-removing machines.

Though some experts think the unsplit nuts might be less mature than the split variety, Ferguson said there really isn't much of a discernible taste difference. Most of the pistachios without shells end up being used in cooking, and to make products such as pistachio ice cream. Ferguson adds that pistachio use as a recipe ingredient is a growing trend in the industry.

Assuming that you're not a person who enjoys the sensual experience of cracking the shell and extracting a pistachio, which is a better deal to buy — with shells, or without? In fact, it is preferred not to introduce excessive water into the shell or to leave the kernels inside the shells exposed to water for very long, as this could saturate the kernel and lead to damage or unnecessary hydration.

As water enters the shell, the kernel or meat of the shell comes in contact with the water. If water is left inside the shells for an extended period of time, the shell and the kernel itself can become hydrated. Accordingly, the methods of the present invention call for the shells to be split open in a relatively short period of time after water is introduced in order to avoid hydration of the kernel or shell of the nut.

Otherwise, a saturated kernel may be damaged or explode when exposed to microwave radiation. It is therefore an important object of the present invention to minimize the amount of time that the shells and kernels are exposed to water. Not only does this facilitate rapid processing of closed-shell pistachio nuts, it also avoids potential damage to the nuts themselves. Should the kernels and shells of the nuts become saturated with water, they may be taken out of the processing system and allowed to dehydrate for later processing.

It is to be appreciated that the amount of time that the closed-shell nuts should remain in the water-bath vacuum is directly related to the amount of vacuum applied i.

A stronger vacuum i. Thus, it is possible to induce the necessary elimination of internal air from inside the nut shells in one minute or less with a very strong vacuum.

Alternatively, this process could take about 10, 20 or even 30 minutes with lesser vacuums. Then, once the desired level of air has been removed from inside the nuts, the vacuum is removed, and water is sucked back into the nuts to replace the expelled air. It is not desirable to expose the nut kernels to this water for more than about 45 minutes without risking hydration of the kernels and resulting damage as described previously.

Thus, once enough time has passed to allow the escaped air to be replaced with water i. The partially water-filled closed shells are then removed from the vessel and microwave radiation is applied to them. The radiation rapidly vaporizes the water within the shell of the nut thereby creating a swift rise in pressure inside the shell. This rapid application of internal pressure causes the shells to split along their longitudinal sutures. Once the shells are spit, the now open-shell pistachio nuts can be dried and further processed.

An important aspect of this process is the speed in which the water in the shell is vaporized to create internal pressure within the shell. As described above, closed shell pistachio nuts are permeable to water and water vapor. Therefore, it is important to increase the vapor pressure or volumetric pressure within the shell at a rate faster than the rate at which water or vapor can escape from the shell. The use of microwave radiation allows for the water to quickly be vaporized.

The microwaves are readily absorbed by the water, but not the shell or kernel of the nut which remain dehydrated. Due to the rapid heating of the water from the use of microwave radiation, the shell, while slightly permeable at its base, is not capable of releasing the amount of pressure created from the water vapor and the shell is forced to split open rapidly.

Before splitting, most, if not all, of the vapor pressure is lost during microwave application through the base region. If the pistachio nut is over-hydrated, allowing the kernel of the nut to become hydrated, then the microwave radiation may act upon the water in the kernel itself, potentially causing it to explode, and therefore rendering the pistachio unmarketable.

It is therefore desired that the kernel of the nut remain dehydrated, or at worst minimally hydrated during this process. If the kernels do become hydrated for any reason, they can be dehydrated and reprocessed without any adverse consequences. Unlike other methods for splitting pistachios, the process described above does not rely on an external mechanical force on the nuts to cause the splitting.

The process inherently has several advantages by not being limited by a physical apparatus. The nuts do not have to be sized as is needed for many machines which requires sizing so that the proper amount of force is applied to all nuts. Additionally, the above described process is extremely fast compared to methods of opening closed shelled pistachios.

The process of inserting water into the shells of the pistachios takes much less time than previous methods that required soaking. The nuts are submerged during the vacuum process, but not for the extended period of time required for the nuts to become completely hydrated.

Whereas soaking the nuts may take hours, the process of using vacuum pressure to fill the shells with water can be accomplished in just a matter of minutes. During the vacuum process, the nuts are exposed to water for a very short period of time preferably minutes and should not be left in contact with water for longer than forty-five minutes to prevent the kernels from becoming hydrated.

In the event that the nuts are left in water for a longer period of time for any reason machine failure, operator error, etc. It is important to cause the expansion of the water within the shell as quickly as possible after the vacuum process.

As described, the shell of the nut is slightly permeable, thereby allowing water to enter the void within the shell. Since the shell is permeable, water that enters the shell of the nut can also slowly discharge over time. Therefore, to ensure that there is sufficient water within the shell of the nut to cause internal pressure, the process of microwaving the nut should occur as soon as practicable after the vacuum process. Rapid timing also assures that the nut kernel will not become hydrated during the process.

Additionally, the process of irradiating the nuts with microwaves is extremely rapid, and can cause the splitting of nuts within less than forty-five 45 seconds. The kernels can be cooked if left exposed to microwave radiation for longer than forty-five seconds. In an alternative embodiment, water can be trapped within the shell from simply soaking the nuts in water for an extended period of time rather than through the use of vacuum pressure as described above.

The nuts should be soaked for a long enough period of time to allow enough water to diffuse inside the shell without substantially hydrating the kernels.

Substantially hydrating the kernels can lead to damage, as describe previously. In this embodiment, water diffusion occurs from outside in, first affecting the shells, and only affecting the kernels if left to soak for too long. Thus, the closed-shell nuts are allowed to simply soak for a long enough period to allow some water to permeate through the shell to the inside, ordinarily about an hour, but generally not for more than about two hours. This allows the kernels to remain largely dehydrated.

When the shells reach an appropriate level of hydration, they are exposed to microwaves as above. The water that has permeated into the shells reacts, creating pressure within the shells and forcing the shells to split open.

In another alternative embodiment, instead of vaporizing the water trapped in the shell, the water can be rapidly cooled. Such rapid cooling causes the volume of the water to increase as it is frozen within the shell.

The water within the shells is rapidly frozen by the use of an extremely cold solution such as liquid nitrogen or an ethanol-dry ice solution. It is to be noted that any method of rapid freezing other than the use of a super-cooled solution is also contemplated by this invention.

The rapid freezing of the water within the nuts causes the expansion of the water as it turns to ice, and the pressure from such expansion causes the shell to split open along the longitudinal suture. The water within the nuts can be frozen extremely quickly, usually within one 1 minute.

After the shells are split by the internal pressure created by the rapid formation of ice within the shells, the now open-shell pistachios are dehydrated and further processed for sale. During this process hydrated kernels may be damaged. If the kernel is hydrated, then the kernel can freeze.

When frozen, the texture and flavor of the nut may change and the nuts become less valuable. Therefore, it is still important to keep the kernels from becoming hydrated before the nuts are exposed to the very cold temperatures described in this embodiment.

Other aspects of the invention are methods and processes for enhancing the degree of splitting pistachio nuts. Some pistachio nuts are slightly open, yet not enough for commercial sale. Therefore the split of the shell must be enhanced. Growing in clusters similar to grapes, pistachios tend to naturally fall off the tree when they ripen, where they are gathered by hand, net, or some other means. According to several sources, most harvesters will also shake the branches with machines to help the nuts fall off.

Good pistachio nuts will split while on the tree, although some will not. Typically, the only pistachios sold in stores are the ones that have naturally opened. In fact, you can break down the research surrounding this nutritional nut into at least six major health benefits, according to Organic Facts:. Read more: All about heart healthy nutrition. In comparison to dried fruits and other nuts almonds, cashews, pecans, etc , pistachios are low calorie, protein rich, and low fat—making this nut the go-to snack for weight management.

This antioxidant is particularly important in healthy vision, as it helps reduce the risk of age-related macular degeneration. As with most nuts, pistachios are great for intestinal health due to their dietary fiber. One ounce 30g of pistachios can contain about 3 grams of fiber, which is more than enough to boost daily digestion.

Pistachios are such a rich source of antioxidants that even their shells contain large amounts of this nutrient, according to researchers from Tarbiat Modarres University.