Preserved fruit is a product with a long history, which is widely spread in traditional famous and special foods in China. Its soft texture, glittering and translucent, durable storage, delicious and beautiful, is not only famous in China, but also enjoys a high reputation in the world. At present, preserved fruits are very popular in China, and the turnover is increasing by about ten times every year.

Raw materials and manufacturing requirements

Most kinds of fruits and some vegetables can be used to make preserved fruits. Due to the difference of texture, water content and organic acid content, the processing methods and conditions of various fruits are also different, but the overall peaceful technological process is nothing more than:

1. Selection of raw materials: The basic principle of preserved fruit is to use the high osmotic pressure of high-concentration sugar solution to separate out excess water in the fruit, absorb appropriate sugar on the surface and inside of the fruit, form high osmotic pressure, inhibit the survival of various microorganisms, and achieve the purpose of preservation. According to this principle, when making preserved fruits, we should pay attention to choosing varieties with low water content and high core content, varieties with beautiful color, tender and tough meat, varieties with good storage and transportation resistance and easy separation of core.

2. Pretreatment: Different fruits have different textures and organizational structures, so different methods and measures should be taken during processing. For example, jujube peel should be cut into uniform stripes before processing, which can accelerate the penetration of sugar solution; For example, preserved apricots should be fumigated before processing. The fruit treated with heavy sulfur can not only avoid or reduce oxidative browning, but also reduce the loss of vitamin C during drying. According to the experiment, the vitamin C content of Rosa roxburghii dried with heavy sulfur is at least 25.84% higher than that of the control group without heavy sulfur, and the highest can reach 58.34%. For example, before processing peaches and apples, mechanical peeling, manual peeling or chemical peeling are used.

3. Preparation of sugar solution: When the water content of normal preserved fruit products is 17- 19%, the total sugar content is 68-72%, and the reducing sugar content is 43%, accounting for more than 60% of the total sugar content, there will be no "back sand" (sucrose crystals appear on the surface or inside of the finished product) and "back sugar" (finished product) When the reducing sugar content is 30% and the proportion of the total sugar is less than 50%, the finished product will return to sand irregularly after drying. Preserved fruits that return to sand lose the luster of normal products and are easy to be damaged, which seriously affects the appearance and quality of finished products; When the reducing sugar content is between 30% and 40%, although the finished product will not return to sand temporarily after processing, there may still be a slight phenomenon of returning to sand after storage, and the degree of returning to sand will decrease with the increase of reducing sugar content; When the content of reducing sugar is too high, the phenomenon of "returning sugar" is easy to appear in high temperature and humid season. It can be seen that the ratio of sucrose to reducing sugar in preserved fruit determines the quality of the finished product, and the main source of sugar in the finished product is sugar solution, so the preparation of sugar solution is the technical key of preserved fruit production, which must be highly valued. Experience has proved that a certain amount of organic acids should be added to the sugar solution of preserved fruits, especially the sugar solution of fruits with less organic acids such as apples, and its pH value should be adjusted during cooking to control the proportion of reducing sugar in the sugar solution. In practice, it is concluded that when the pH value of sugar solution is adjusted to 2-2.5, after 90 minutes of cooking, most of the sucrose can be converted and the product quality can be guaranteed.

4. Boiling: There are basically two kinds of boiling methods for various preserved fruits: (l) the second boiling method, and the first boiling method is mainly used for processing fruits with low water content, large intercellular space and loose tissue structure, such as

Apples, dates and the like. The specific cooking and soaking time depends on different varieties. However, the production of preserved fruit in some areas in the south is slightly different from that in Beijing. For example, preserved fruits such as peach slices and plum slices produced in Fujian should be peeled, cracked and pitted before use.

Soak in 0.2% lime water, then blanch and sugar stain, and make it by one-time cooking method. (2) Multiple cooking method is suitable for fruits with high water content, thick cells, dense tissue structure and easy erosion during cooking. Because this kind of fruit is cooked thoroughly at one time, not only the sugar solution is difficult to penetrate into the fruit, but also it is easy to cook thoroughly, even into jam, so the method of cooking thoroughly and soaking for many times is adopted. For example, peaches, pears and apricots are all processed by various cooking methods. Some pears are not easy to cook, but because of their high water content, it is difficult for sugar to penetrate into them. In the cooking process, a large amount of water in the fruit oozes out under the soaking of sugar solution, which dilutes the concentration of sugar solution. If the cooking time is prolonged, the cost will inevitably increase, so the method of multiple cooking is generally adopted. In addition, protein cell protoplasm in fruit can be solidified by heating by multiple boiling, which has better permeability. At the same time, various enzymes in diced fruit were destroyed by blanching, which was beneficial to prevent tannin from oxidative browning and maintain the delicious color of fruit.

5. Dehydration and drying: Dehydration and drying is the last process of preserved fruit production, and its purpose is to remove excess water in the fruit, so that a layer of "sugar coating" is formed on the surface of the product, which inhibits the survival of microorganisms everywhere and achieves the purpose of long-term preservation. Due to the different finished products of preserved fruits, the drying degree and time are also different.

Several processing methods of preserved fruit;

1. preserved apple

(l) The main raw materials (based on the production of100kg finished product) are apple160-180kg and sugar 70kg.

(2) Material selection and pretreatment. Generally speaking, Guoguang, Wojin and Hongwu are more suitable for making preserved apples. When making, select the intact fruit without damage, pests and diseases, peel it by turbidity method or chemical peeling method, break it, remove the core and wash it with clear water.

(3) Sulfur fumigation: The apples treated in the previous step need to be fumigated. Fumigation is to burn sulfur in the air to produce sulfur dioxide, which is dissolved in fruit juice. Because sulfur dioxide has strong reducibility, on the one hand, it takes away the oxygen needed for tannin oxidation; On the other hand, it inhibited the activities of various enzymes in the fruit to a certain extent, thus effectively preventing the browning of the fruit. The fumigation amount is about 0.2-0.3% of the fruit raw material, and the time is 30-60 minutes.

In addition, soaking in sodium bisulfite solution can also be used instead of fumigation. The concentration of sodium bisulfite solution used is generally 0.3-0.6%, and the soaking time is 30- 1.20 minutes.

(4) Boiling: Take 30 kg of clean water, 45 Hall of sugar and citric acid, put them into a pot to make sugar solution, then add the processed apple 1 10 kg, boil for about 10 min, and then heat. Take out some fruits, pour in 5 kilograms of 50% sugar solution when it becomes soft, and add the sugar solution twice after the sugar solution is boiled. After boiling, add 3-5 kg of dry sugar and 1-2 kg of concentrated sugar solution in three times with an interval of about 10 minute. Finally, according to the cooking situation, sugar is added 2-3 times, each time 10-20 kg. After adding sugar for the last time, cook for about 20 minutes. When the concentration of sugar solution reaches more than 65%, pour it into the tank for soaking. Note that the whole cooking time is about 1.5-2 hours and the soaking time is L-2 days.

(5) Drying and dehydration: take out the soaked apples, put them on a bamboo drawer to drain the sugar solution, and send them to a drying room at 60-70℃ for baking or sun drying. When the surface of the fruit is not sticky and the water content is 20%, it is taken out and trimmed, and the unqualified products are removed to obtain the finished product.

2.preserved apricots

(l) The main raw materials (based on 100 kg of finished products) are 350-360 kg of apricots and 60-65 kg of sugar.

(2) Material selection and pretreatment: the color of the fruit used in preserved apricots should be golden, the fruit is easy to leave the pit, the meat is tender, tough and storable, not soft after ripening, and not damaged by pests and diseases. In production, "Tiebada" and "Big Flat Apricot" are generally ideal. After picking, the fruit splits along the syncline, and the core is removed and washed. However, the green apricots producing green plums were soaked in 15% salt solution for 3 days to separate the pulp from the stone, pressed out the stone with a flat plate, cut, bleached with clear water to remove salt, and treated for later use.

(3) Smooth fruit thinning treatment, that is, fumigation and fruit thinning are carried out on the treated fruits, and the specific method and dosage are the same as that of sulfur fumigation treatment of apples.

(4) Boiling, that is, the treated fruit should be boiled. Because apricots have high water content and dense cell tissue, they should be cooked and soaked many times. Preserved apricots are best cooked in a copper pot, and stainless steel pot can do the same. The first cooking uses 35-40% sugar solution (the remaining sugar solution from the second cooking can also be used for continuous production). Because apricots contain more organic acids, there is no need to add citric acid to convert sucrose, and the cooking time is about ten minutes. But in the cooking process, we should pay attention to turning it gently to ensure uniform heating. When the surface of the fruit is slightly swollen and small bubbles appear, pour it into the jar for soaking. The soaking time is generally l2-24 hours, and the fruit should be immersed in the sugar solution.

The sugar content of the sugar solution cooked for the second time should reach 50% (you can add sugar or use the sugar solution left over from the third time). Cooking time is generally 2-3 minutes. Take it out after boiling, drain the sugar solution and put it on a bamboo drawer to dry. In the process of cold drying, the water evaporates quickly, and the concave surface of the fruit faces upward, and the water evaporation is about 1/3 of the original weight.

The sugar concentration of the third boiling is 56%, and the boiling time is 15-20 minutes. In the cooking process, the concentration of sugar solution increases with the continuous evaporation of water. When the sugar content reaches more than 70%, take out the fruit, drain the sugar solution, and evenly put it on a bamboo drawer to dry. After drying until it doesn't stick to hands, the fruit still has toughness, which is the finished product.

3. Preserved fruit made of candied dates is generally called candied dates. Because of its fine lines, it is also called golden silk candied dates.

The raw materials for making candied dates should be varieties with large fruiting body, small stone, thin peel, loose pulp cell tissue, low water content and high sugar content. Commonly used varieties are "Datangzao" and "Tin Foil Jujube". The raw materials for making candied dates are suitable for turning from green to white, and overripe or overripe fruits are not suitable for processing. In the processing of candied dates, one-time cooking is generally used because it is easy to absorb sugar solution.

Before the candied dates are boiled, many fine lines should be drawn on the jujube skin along the direction of the dates, and the depth of the cut should be based on the penetration of the cortex, and then boiled dry according to the method of preserved apples.

Fresh dates 120- 150 kg for each 100 kg of candied dates, and 60 kg of sugar.

4. Peaches are mainly white meat varieties, such as "Juehongyao" and "Dayebai".

Peaches can be peeled manually or chemically (fresh peaches are boiled with 4-6% sodium hydroxide solution, then soaked in liquid for about 10 minute, then stirred in clear water, and peeled by mutual friction), then cut into two halves, pitted, fumigated and cooked. Boiling can refer to the method of preserved apricot, but the boiling time is: the first time 10 minute, the second time 4-5 minutes, and the third time 15-20 minutes.

In the production of preserved peach, because the fruit contains less acid, the sugar solution should be prepared according to the apple sugar solution, and citric acid should be added appropriately.

Every 100 kg of peaches uses 400 kg of fresh peaches and 65 kg of sugar.

5. The material selection, sugar solution preparation and pretreatment of preserved pear can be carried out with reference to apples. However, due to the high water content of pear fruit, it is boiled for three times: the first time for 5-7 minutes, the second time for 10- 15 minutes, and the third time for boiling.

20 to 30 minutes.

Every 100 kg of preserved pears uses 450-500 kg of pears and 60-65 kg of sugar.

6. Selection and treatment of raw materials for orange cake (L), mainly small red oranges, which are harvested when they are ripe. The peeling or peeling of fresh oranges depends on the product specifications. First, the raw materials are sliced and squashed with a slitter, then the seeds are extruded, soaked in 2.2% lime milk for several hours, hardened, rinsed with clear water and pre-cooked for several minutes.

(2) sugar production. Sugar making of orange cake generally adopts the method of combining honey making and boiling sugar. For example, the sugar system of Sichuan orange cake is based on 50 kilograms of orange embryo and 25 kilograms of sugar. Firstly, 9 kg of sugar is put into a pot and dissolved in water (the amount of water is equal to the degree of flooding the orange embryo), then the sugar solution is poured into the orange embryo to be absorbed. After the sugar permeates, the remaining sugar is added, and then the orange fruit is heated and boiled until it is completely transparent. When the boiling temperature reaches 108-l 10℃, turn off the fire and drain the sugar solution. Cool, flattening, air dry, and sprinkling dried sugar powder on that surface of the fruit.

7. Mume Mume is one of the cold fructose products, and its finished product contains salt, sugar and acid, licorice and various spices. It is a kind of travel food that can help digestion and relieve summer heat. The processing methods in different places are roughly the same, with different ingredients and slightly different tastes.

Raw materials and ingredients. When making preserved plum, we should choose a variety with big fruit, thick flesh and small kernel (such as Sanhuamei) and harvest it when it is ripe. You can also use immature hard fruit drops as raw materials, sugar or brown sugar as sugar, and licorice, citric acid, essence, food pigment and so on as ingredients.

(2) Processing method

First, the embryo-making raw materials are washed with water, so people stir and scrape the skin in rolling cylinders and pottery pots, then marinate with 10- 15 Jin of salt 15-20 days, and marinate in wooden barrels or water tanks. First put a layer of fruit (about 2 inches thick) and remove a layer of salt (about 0. Take out a layer of l5 and dry it for 20 days. Drying in the sun forms thousands of embryos. In order to increase crispness, 200 grams of alum or 300 grams of quicklime were added to 100 kg of fruit during curing.

Desalination: put the dried embryo into a flowing water tank (with a water inlet pipe at the bottom) or a water tank (changing water twice a day) and soak it for 1-2 days, remove 80-90% of the salt, take it out and dry it in the sun until it is semi-dry.

Soak sugar in boiling licorice sugar solution. Add 60 kg of water to 3 kg of licorice and 0.2 kg of cinnamon, boil and concentrate to 50 kg. Clarifying and filtering, adding 20kg of sugar and100g of saccharin to half, and deeply dissolving into licorice sugar solution. The second step is sugar soaking, that is, 100 kg of plum embryo is poured once while it is hot, soaked for 12 hours, taken out and dried. After drying in the sun until it is half dry, put it back into the container, then add the remaining licorice juice into the sugar solution that has not been completely absorbed, add 3-5 kg of sugar, 10 g of saccharin and a small amount of citric acid (about 100 g), mix and cook, and then pour it into the container filled with plums. Soak for 8- 12 hours, and take it out for exposure after saturation. After drying, 3 kg of licorice powder is mixed with a little essence and pigment to get the finished product. The surface of the product is grayish brown with a small amount of licorice powder.

The processing method of preserved plum is the same as that of preserved plum, except that citric acid is not added or less.

8. Pei-Mui Chan Pei-Mui Chan is also a kind of candied fruit, which is very popular in domestic and foreign markets because of its unique flavor and beautiful packaging.

This processed product has different names: named after different jams, such as dried tangerine peel, plum, Pei-Mui Chan, dried tangerine peel and mango. If the off-season fragrance is different, add the names of spiced plum, Liuhe plum, Bazhen plum, Huijin plum and other materials to the fruit name. Pei-Mui Chan's processing method is introduced as follows:

(l) Sauce-making: Boil the orange peel stored for more than one year with water for 15-20 minutes, and then rinse with clear water until bitter. After draining, put it into a beater for pulping (or grinding it into pulp), and then cook it into orange peel pulp according to the ratio of one pulp to two sugars (the concentration is subject to pouring out without flowing).

(2) Soak plum embryo in sugar solution (the same as the processing method of preserved plum) and dry it in the sun.

(3) stir while it is hot according to that ratio of multi-embryo with little sauce or multi-embryo with little sauce, and put the embryo on the "peel" tangerine peel sauce. The finished product can be canned or imitated with fruit candy to improve the appearance.

9. Apple jam First, clean the apples, peel them, cut them into pieces, remove the core, cut them into small pieces, add 1/5 water to the pulp, and cook for 20-30 minutes to fully soften the pulp; It can also be softened by steam. Then beat it a little (not too bad) and add sugar to concentrate it. eat

Firstly, sugar is prepared into a 70% solution, which is added in l-2 times, and 70-80 kg sugar is added to 100 kg pulp. Concentrate to 105- 106℃, and the solid content reaches more than 68%, and then take out the pot. Cooling to 70℃, canning, sterilizing (20'-25'/ 100℃), and cooling.

10. The raw materials of peach and plum sauce should be thoroughly washed with water before processing. Because peach skin is covered with fluff, 0.5% alum can be added to water to help depilate. Then rinse with clean water ☆ cut open and remove the core, and add water to the pot. The water quantity is l/10 of the pulp; Boil 10 minute, add sugar to concentrate, add 80-100 kg sugar to100 kg pulp. Sugar solution is added to 1-2. In the process of concentration, large pieces of fruit are constantly stirred and crushed. Peach and apricot jam need not be beaten, which reduces working procedures and shortens processing time. Boil until the boiling temperature is l05- 106℃, and the solid content is 68%. Cooling to 70℃, bottling, sterilizing (20'-25'/ 100℃), and cooling.

Ll, exotic jam kiwi fruit can be made into canned sugar water, wine or jam. Transparent, brownish yellow, sweet and sour, nutritious, well received at home and abroad. First, classify the raw materials, select fully mature (at least eight ripe) fruits, remove the spoiled fruits, and then wash them twice with clear water. Peeling, peeling can be done by hand, or you can cut it in half first, then dig out the pulp with a core digger and add sugar to cook the sauce. 100 male meat match 100 Jin of sugar. First, the sugar is mixed into 75% sugar solution, and after the first boiling with L/2, the pulp is poured into it to boil, then the remaining sugar solution is added and boiled for 30 minutes. When the boiling temperature reaches 105℃ and the soluble solid content reaches above 68%, take out the pot, can, seal and sterilize (20 '-25 '/ 100).

12. Select rotten fruits from jujube paste, wash them with clear water, add 40-50% jujube and cook until soft and rotten. Mash into paste, sift the pulp, peel and core. Add 25 kilograms of sugar to 50 kilograms of pulp, cook until the boiling point is 107℃, take out and cool.

13, hawthorn jelly Wash the hawthorn, cut into sections, and remove the fruit stalks and calyx. Add L- 1.5 times the weight of hawthorn, heat and boil for 10 minute, take it out and soak it in water for 12-24 hours. When the juice is bright red and sticky, filter it with a fine screen or cloth to get clear juice. Pour the juice into the pot, heat and evaporate some water, then add sugar to make it shrink deeply. The amount of sugar added depends on the pectin content in the juice, with high pectin content, low pectin content and increased sugar content. Generally, the ratio of sugar to leachate is 1: 1 or 0.5: 1 or 0.3: 1. After adding sugar, cook until the boiling point temperature is 104- 105℃, stick the fruit juice in the air with a wooden board to form a flaky drop, and then take it out of the pot. Cool to 75℃, canning, seal, sterilizing (20'-25'/ 100℃), and cooling.

14, peony bark peony bark mostly uses plants with high acid content and pectin as raw materials. After precooking, beating and sieving, the fruit is added with 10% sugar, and heated and concentrated into thick mud. It is also used to mix persimmon and jujube with high sugar content, without adding sugar, take it out after concentration, and spread it evenly on cloth or baking tray with a thickness of about 0.5 cm. Send it to the drying room, and when it is dried to a tough skin shape, take it out and sprinkle it on the back of the cloth, and then spread the fruit paste on the glass plate, which can be dried at one time. The above finished products can be sold directly, or a layer of sugar can be removed from the finished products, rolled into small rolls, cut into small pieces or pieces, and packaged in transparent cellophane or plastic bags for sale.

15, pineapple juice

(1) The raw materials are fruits, kernels, thorns, juicing, filtering, adjusting sugar acidity, preheating, canning, sealing, sterilizing, cooling, canning and packaging.

(1) raw material processing and juicing uses pineapple as raw material. Before juicing, it should be cleaned, cut off the head and tail, and peeled. Stone, thorn and minced meat can be collected and squeezed directly. The mesh size of the press should be 0.5-0.6 mm.

② The filtered juice should be filtered quickly, and the residence time should not exceed 15 minutes.

(3) Regulation of sugar and acidity. Firstly, the soluble solid content and acid content of filtered juice were determined, then the soluble solid content was adjusted to 65438 03% with 50% sugar solution and the acid content was adjusted to 0.7% with citric acid.

④ The adjusted preheated juice should be preheated in time, and the residence time should not exceed 15 minutes. The temperature of the preheated juice should be 65-70℃.

(5) canning, sealing, sterilizing the empty cans, and canning the preheated juice immediately. General requirements are canning in advance and sealing immediately after canning.

⑥ Sterilize with boiling water immediately after sealing.

Sterilization formula: 200g (2'-5'100℃) or 500g (3'-6'/ 100℃).

⑦ Immediately after cooling and sterilization, put it in cold water and cool it to 40℃.

Matters needing attention

In the process of preserved fruit production, due to the different types and quality of fruits, the operation methods should be changed accordingly, but even so, due to lack of experience or other reasons, unqualified phenomena often occur. The common problems in production are:

(1) The phenomenon of "sand returning" and "soup flowing" occurred in the production of preserved fruit. Because the proportion of reducing sugar in sugar solution is not suitable, it often causes the defects of "returning sand", "flowing soup" or "returning sugar" For the solution of these phenomena, please refer to "Preparation of Sugar Solution".

(2) Boiling shrinkage.

In the process of preserved fruit processing, improper selection of fruit varieties, inaccurate heating temperature and time, incorrect pretreatment method and insufficient sugar soaking will all lead to boiling and drying shrinkage. The solutions to these problems should be constantly adjusted and improved on the basis of small batch production.

① Boiling problem In the process of making preserved apples, boiling is a relatively easy problem, and the common measures are as follows: a) Choose the ideal fruit varieties according to the previous regulations; B) The maturity of apples should be suitable; C) blanch with 1% salt water for several minutes before cooking.

The methods to avoid boiled candied dates are: a) selecting suitable varieties; B) Selecting fruits with appropriate maturity; C) When marking, it should not be too deep or staggered.

(2) The main reasons for dry shrinkage are: a) insufficient sugar absorption due to insufficient fruit maturity; B) Insufficient sugar absorption caused by insufficient sugar concentration in the brewing process. The solution can be to adjust the sugar concentration and soaking time appropriately.

(3) Browning problem In the process of preserved fruit production, browning is also a problem that affects product quality. The main reasons for this problem are: a) tannin oxidation; B) non-enzymatic browning; C) The baking conditions are incorrect. The measures to avoid and solve this problem are: a) fumigation or scald with sodium bisulfite solution; B) blanching treatment; C) The interaction between sugar solution and some protein in fruit will produce a reddish-brown melanin. This protein is directly related to cooking time, temperature, acid content in sugar solution and invert sugar content. Therefore, under the premise of blanching and cooking, the time should be shortened as much as possible. D) Browning caused by baking can adjust baking temperature, improve ventilation conditions, and solve the browning problem accordingly.

(4) the problem of mildew. Due to insufficient sugar absorption, the finished preserved fruit often suffers from mold pollution, that is, mildew. The solution is simple. In general, when the total sugar content in the finished product reaches more than 68%, it is difficult for any microorganism to survive.

Boil the sugar solution, filter it after use, and add appropriate amount of starch to make preserved fruit.

The production of preserved fruit, like other foods, is influenced by raw materials, auxiliary materials and production conditions. In order to improve product quality and ensure the inherent color, aroma and shape of food, we should master it flexibly according to the characteristics of different fruit varieties and other specific conditions.

The phenomenon of "returning sand" in preserved fruit and its prevention methods

Because candied fruit and candied fruit are generally made by sugar boiling process, the temperature is high, and sucrose is generally used. When the storage temperature is lower than 10℃, it is easy to crystallize out and "return to sand". In addition, if the content of glucose in the product is high, it is easy to crystallize.

In order to avoid sugar returning to sand, some maltose (a mixture of maltose, glucose and dextrin) or starch syrup (maltose, glucose) or honey (containing glucose and fructose) is often added in sugar making. Because these sugars can inhibit the growth of crystal nucleus and improve the saturation of sugar solution, so as to prevent sucrose from "sand control". In addition, for raw materials with less acid content, a small amount of tartaric acid and citric acid can be added when making sugar, which is beneficial to the conversion of sucrose. When the content of invert sugar reaches 30% ~ 40%, the purpose of preventing "sand returning" can also be achieved.

The water content of normal preserved fruit products is 17- 19%, and the total sugar content is 68-72%. When the reducing sugar content is 43%, accounting for more than 60% of the total sugar content, there will be no "back sand" (sucrose crystals appear on the surface or inside the finished product) and "back sugar" (glucose crystals appear in the finished product), and the product quality is the best. When the reducing sugar content is 30% and the proportion of the total sugar is less than 50%, the finished product will return to sand irregularly after drying. Preserved fruits that return to sand lose the luster of normal products and are easy to be damaged, which seriously affects the appearance and quality of finished products; When the reducing sugar content is between 30% and 40%, although the finished product will not return to sand temporarily after processing, there may still be a slight phenomenon of returning to sand after storage, and the degree of returning to sand will decrease with the increase of reducing sugar content; When the content of reducing sugar is too high, the phenomenon of "returning sugar" is easy to appear in high temperature and humid season. It can be seen that the ratio of sucrose to reducing sugar in preserved fruit determines the quality of the finished product, and the main source of sugar in the finished product is sugar solution, so the preparation of sugar solution is the technical key of preserved fruit production, which must be highly valued. Experience has proved that a certain amount of organic acids should be added to the sugar solution of preserved fruits, especially the sugar solution of fruits with less organic acids such as apples, and its pH value should be adjusted during cooking to control the proportion of reducing sugar in the sugar solution. In practice, it is concluded that when the pH value of sugar solution is adjusted to 2-2.5, after 90 minutes of cooking, most of the sucrose can be converted and the product quality can be guaranteed.

The phenomenon of "sand returning" and "soup flowing" appeared in the production of preserved fruit. Because of the improper ratio of reducing sugar to total sugar in sugar solution, it often causes the defects of "returning to sand", "flowing soup" or "returning sugar" For the solutions to these phenomena, please refer to "Preparation of Sugar Solution".