Drying Process Of Goji Berry

The fruit of goji berry is ripe in 6~11 months. The fruit can be picked when the fruit turns from green to red and the flesh is slightly spongy. If premature pick, the fruit is not full, dry color is darker; if too late picking, sugar is too large and easy to fall off, after drying the color is darker, affecting the appearance. Picking fruits should be carried out after 10 in the morning. Don’t pick them after rain. Take them lightly when you pick them, and pick them together with the fruit handles. Otherwise, the juice will affect the quality of the outflow.

The drying process of goji berry is divided into three stages

The first stage is the rising speed drying stage. Dry room temperature up to 35 DEG -40 DEG, circulating wind speed 2.3 m / s, air fresh water evaporation to make the diffusion free state quickly, especially the pericarp water loss reached 50%, skin wrinkles, structure of water pulp began to slowly seeping from the cortex of stomata, fruit sugar concentration increased, the inhibition of enzyme activation the activity of protection the main components of polysaccharide, vitamins, amino acids, especially the protection of the red pigment is good. Dry fruit has a beautiful color.

The second stage is the constant speed drying stage. Due to water leakage in the fresh fruit, non binding water gathered sufficient peel, this is because the surface of the water vapor pressure and temperature pressure is basically the same, the internal moisture quickly moved to the surface of the fruit compression in order to meet the needs of skin moisture vaporization. When the water loss rate of fruit reached nearly 50%, the indoor temperature rose to 50 -55, and the cycling speed decreased. The less water contained, the shorter the dehydration time. A large number of dehydration, so that the shape of the fruit shrink, half dry state, this period weighing, measuring water, fruit containing about 30% of water.

The third stage is slow down drying stage. When the fruit is cut down to about 30%, the thermal conductivity of fruit becomes small, inside and outside temperature increases, when the indoor hot air to reach 55 degrees -60 degrees, because the fruit in less moisture, moisture migration rate of evaporation decreased, water exudation is slow, so the need for a time to slow discharge.

A common phenomenon is the fruit of Goji berry fruit drying the moisture diffusion surface is greater than the internal diffusion rate, fruit containing free water leakage rate is greater than the structure of water leakage rate, this is because the Goji berry fresh high fructose dehydration leads to difficulties. If the temperature is too high, the surface water of fresh loss too fast, and water and fruit extravasation for not up, then the skin will bubble, blocking the drain holes, but the fruit in water can not discharge, the decoloration, decrease the quality of cortex has. So the first fruit surface grease maceration, suitable temperature and wind speed plus in dehydrated skin at the same time through holes penetrate fruit temperature inside the fruit, to discharge the water, so as to speed up the drying speed and drying quality assurance.

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1. The drying technology of goji berry

The purpose on drying goji berry is to store nutrition for a long time without destroying. By drying out some water, the concentration of soluble matters will be increased to an extent that can’t be used by microorganisms. Drying is a way to remove the moisture from fresh fruit of goji berry by the heat energy. The drying process is a complex combination of thermal, diffusion, biological and chemical phenomena.

2. The drying mechanism of goji berry

Humidity gradient and temperature gradient are the inner motivation of drying goji berry. While drying, the surface moisture of the fruit is more than the equilibrium moisture and evaporated, and the moisture inside spread to the outside. The higher the humidity gradient and temperature gradient are, the faster the water spread. The water diffusion will cease if the internal and external water content of the fruit achieve balance.

During the drying process, the moisture diffusion inside is slower than the evaporation on the surface, which will affect the drying speed. Therefore, controlling factors of drying reasonably can accelerate the internal moisture diffusion and drying. However, if the temperature of medium is changed, the water on the surface will be evaporated quickly and the hard shell will be produced, which will delay the speed of drying, in addition, because of the big difference between inside and outside moisture, it will bring some internal stress and even cause a cracking to the fruit.

3. Influencing factors of drying

During the drying, speed determines the quality of goji berry, the drying speed is related to the drying method, and will be influenced by heating methods, temperature, medium temperature, humidity, air velocity, fruit and state. 

Drying methods of goji berry

We have accumulated valuable experience and summed up a lot of drying methods in actual production and scientific research. Here are some drying methods of goji berry.

1. Aired-drying is a natural drying method with using ventilation and sunshine. Ningxia old farmers often collected and laid the fresh goji berry which is about 2em thick in an open ventilated place with fruit racks for drying. Generally, summer fruit can be dried for 4-5 days, but for autumn fruit, maybe 7-9 days. Fresh fruit should not be exposed to strong light for the first two days. As for this drying method, it is the most economical one but with long time and losses. The fruit is easy to be putrid and polluted by dust, flies and rats.

2. Hot air drying is a method of drying with drying machine, heating air by hot-blast stove and sending the hot air to the fresh fruits to heat up. There are some data suggested that goji berries should be first heated at 40-45℃ with wind speed of O.15m/s for about 6 hours, and then at 6o℃ with wind speed of 0．35m／s for 6 hours, finally at 65℃ with wind speed of 0.25m／s for about 20 hours. Above all, this method has the advantages of low cost, large processing capacity and easy operation, but will also cause the losses and low qualities.

3. The method of drying goji berry whose equipment is vacuum freeze dryer has been widely used in Ningxia, Tianjin and other places. This machine freezes immediately the water in the fruit, and then makes the ice sublimate to steam and remove in vacuum. While drying, fruit should be frozen at -30℃ at first with the pressure of 30Pa, and then be heated at the temperature no more than 70℃ for 20 hours, finally it could be stored hermetically. Goji berries dried by this method will have advantages of bright red color, less loss of nutrients, high drying quality, low moisture content (less than 3%),convenience of saving and high value-added rate. But the equipment is expensive.

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Three kinds of dry fruits taste quite different when chewing, freeze-dried goji berry has a very crisp like potato chips, tastes sweet, melts in the mouth. While the oven-dried goji berry is full of adherent flesh, tastes like raisins and has the highest sweetness; air-dried goji berry is the easiest to chew with a little bitterness.

Analysis and conclusion: freeze-dried goji berry has the best taste and is suitable for snacks. As for the mouth feel, oven-dried goji berry comes second, but  it is the sweetest one above all, and it is also suitable for chewing. Air-dried goji berry is not suitable for direct chewing with bitterness and hardness.

5. Soaking in water

Soak some goji berries into warm water and then make an observation.

Freeze-dried goji berry: easy to absorb water and quickly restore to the original state, water is light, clear, the flesh is soft and floating on the surface of the water.

Oven-dried goji berry: is slow to absorb water, can not quickly restore to the original state, the color of the water gradually turned dark red with turbidity, most of fruits sink in the water and are still full of flesh after removal.

Air-dried goji berry: can not be restored to the original state without significant change, can change the water color and float.

After adding warm water to the cup with some goji berries, freeze-dried goji berries are quick to restore to the original state, its color becomes common. oven-dried goji berries sink in water because of its big and heavy volume. Air-dried goji berries show its colors after soaking.

5 minutes later, in the cup of freeze-dried goji berries, the water is clear and amber; in the cup of oven-dried goji berries, the water is dark with a little turbidity; in the cup of air-dried goji berries, the water is light yellow.

After soaking for 5 minutes, freeze-dried goji berries basically restore to the original state of the fresh, and retain its smell. Air-dried goji berries changed little in shape.

Analysis and conclusion: freeze-dried goji berry maintains the overall shape of the fresh, and is similar to the fresh in taste and smell. Oven-dried and air-dried goji berries are shriveled, its taste and smell are quite different from the fresh. And the oven-dried berry is sweeter than the air-dried.

Due to the influence on flesh while soaking goji berry in water, the water color changes significantly. After a long manufacturing on oven-dried and air-dried goji berries, their structures of flesh change greatly, so after soaking in water, the pulp material move out and quickly change the color of the water, which also shows that these two kinds of process may cause the loss of nutrients.

Conclusion: different process cause different results on fruits’ shape, smell, inner structure, and the condition in water. Consumers can choose according to their own needs. Among them, freeze-dried goji berry produced by low temperature freezing technology which can remove the flesh in the water without damaging other nutrients. This kind of technology can keep the original shape and fresh fruit flavor of goji berry with no pollution and zero adding process, but it is brittle and fragile that it is not convenient to store for families. Freeze-dried goji berry can be packaged as a snack. Oven-dried goji berry contains high proportion of water, so the flesh is abundant. Air-dried goji berry makes the most sales in the market, its process is easily influenced the environment. People should be careful while selecting and eat it after cleaning.

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Comparison: a random choice of freeze-dried, oven-dried, and air-dried goji berries.

1.Production process

(From left to right are freeze-dried, oven-dried, and air-dried goji berries.)

Freeze-dried goji berry: means goji berry will be frozen solid by using Vacuum Freeze Drying technology which can make fruits dewater and desiccate by sublimation of ice under the condition of low temperature and pressure.

Oven-dried goji berry: means people accelerate the evaporation of water to achieve the purpose of drying by increasing the temperature of drying room artificially.

Air-dried goji berry: means people remove fruit wax on the surface with lye, then evaporate water from fresh fruit by turning them in the environment with full of sunshine and wind.

Analysis and conclusion: as for freeze-dried goji berry, under vacuum condition, water sublimate from its solid, the material itself is left in the frozen ice shelf, so the dried volume won’t be changed and goji berry will become loose, porous with good rehydration performance. Retaining the color, aroma, taste, shape and nutrition of the original food is the strongest feature on freeze-drying technology. Therefore, freeze-drying food is also known as space food, and nowadays, it is a natural, green, safe and convenient food.

For Air-dried goji berry, goji berry will be destroyed what will cause the loss of nutrient and darkening. Some unscrupulous factories fumigate with sulfur or dye the fruit to make it look delicious, so that the goji berry was changed from tonic to poison.

The technology of oven-dried goji berry is between the freeze-dried and air-dried. We will continue to evaluate other projects to let you know which one suits you most.

2. Appearance and shape

Freeze-dried goji berry: bright-colored, particles plump, dry with its original shape.

Oven-dried goji berry: dark red, slightly shiny, a little plump with flesh texture and irregular shape, not so dry on surface.

Air-dried goji berry: dark red, mat, shriveled, hard, and dry with some foreign matters.

Analysis and conclusion: due to the different production process, dry goji berry shows great difference on its appearance. Comparing with oven-dried and air-dried, freeze-dried goji berry is bright and full; oven-dried goji berry looks more like abundant than the air-dried goji berry, because the opening making environment may bring some sands on the surface, fruits are easy to be influenced in this way.

3. Smell after  cutting

Freeze-dried goji berry: can be cut easily, the internal pulp and fruit seeds are dry and dispersed gives fruity scent.

Oven-dried goji berry: pulp tissues are clearly visible, soft to touch, dry, without significant smell after cutting.

Air-dried goji berry: dry inside, a little flesh, loose structure, without significant smell.

Analysis and conclusion: we can easily find that freeze-dried goji berry is pretty dry after cutting, its peel and pulp are easy to break; during oven-drying, goji berry is affected by heat and become soft, which make it adherent, while compared with the other two kinds of samples, air-dried goji berry is dryer, harder, with more water and less flesh.

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