Why can’t I make “Erbin Frozen Pears” in the refrigerator?

Why can’t I make “Erbin Frozen Pears” in the refrigerator?

Recently, Erbin’s frozen pears have become popular all over the country. Many Northeasterners say: Frozen pears eaten when cut open have no soul. The correct way to eat frozen pears is to take a small bite and suck the juice inside directly. After ruthlessly sucking away the juice inside, only a layer of black outer skin will be left. This method of eating is also commonly known as the “vacuum smoking method”.

There are also many people who have never heard of “frozen pears”. Even if they see the dark autumn color, it is easy to misunderstand that “it has gone bad.”

What’s going on with this dark frozen pear?

Why are frozen pears so dark?

Most of the water in pears is stored in the vacuoles of the cells. When pears are frozen, the water in the vacuoles freezes into ice and increases in size, breaking the cell walls and releasing the polyphenol oxidase originally locked in the cells.

Pear peel is rich in plant polyphenols, which is a type of polyphenols. It undergoes a relatively slow oxidation reaction with oxygen in the air under the catalysis of polyphenol oxidase. Polyphenols are first converted into quinones, and then undergo a series of dehydration and condensation reactions, finally forming brown pigments.

For pears, the activity of polyphenol oxidase and the content of phenolic substances in the peel are much higher than in the pulp, and the skin is in direct contact with oxygen, so the peel will undergo a browning reaction during the freezing process. The pulp inside can still remain light yellow.

What is the quinone substance that causes the color change in this process?

Quinone is actually an organic compound. The simplest quinone is benzoquinone. Judging from the molecular structure of quinones, their molecules are more stable and can absorb and reflect light in the visible light band after being specially modulated. Therefore, quinones are generally colored. For example, para-quinone is mostly yellow, and ortho-quinone is mostly red or orange. Quinone and phenol are two chemical substances that are particularly easy to transform into each other, forming a redox system. Frozen pears are actually mainly the result of phenolic substances turning into quinone substances.

Why are frozen pears so sweet?

Generally speaking, the sugars contained in fruits include fructose, glucose, sucrose, etc., among which fructose has the highest sweetness. Fructose is also very special. It has two chemical configurations, fructose furanose and fructose pyranose. The latter is about 3 times as sweet as the former. When the temperature is below 40°C, as the temperature decreases, fructose furanose will gradually convert into fructose pyranose, which is sweeter.

The fructose content in pears is still relatively high. The main reason why frozen pears become sweeter is that the fructose they contain is converted into the sweeter fructopyranose at low temperatures.

Everyone likes to eat iced watermelon in the summer, because the fructose in watermelon will be converted and become sweeter after freezing.

Interestingly, the sugar in fruits such as peaches and plums is mainly sucrose, and their sweetness does not change significantly as the temperature rises and falls, so their sweetness does not change much after freezing.

Any tips for making homemade frozen pears?

There are so many varieties of pears. Is it possible to use any variety and the frozen pears will be delicious? This has been studied before.

The research team picked 59 kinds of pears from various regions, including Qiubai pears, Apple pears, Yali pears, Korla fragrant pears, and Huangguan pears. After freezing and storing them, they conducted a detailed analysis of the skin and pulp, including the delicate taste of the pulp. degree, sweetness and sourness, juice content, whether the peel is easy to peel off, etc. Based on comprehensive data analysis, they found that Qiubai pears are more suitable for frozen pears. After freezing, they will have a more delicate taste, higher sweetness, and rich juice, which can be sucked in a vacuum.

It is said that in the northeastern region where it is cold enough, you only need to bury the pears in the snow and freeze them for 4 to 5 days. When you take them out, they will be dark and frozen pears. It is recommended to bury it deeper, otherwise, when you look at it, you may find that the pear you buried in the snow was pulled out by some greedy little animal and took a bite…

Some netizens in the South have recommended a method for producing frozen pears in the refrigerator: the main operation is to freeze pears repeatedly, that is, put the pears in the refrigerator to freeze, then take them out to defrost, and then put them in the refrigerator to freeze again. This operation is repeated for 4 to 5 days. . Their reason is that this operation can simulate the temperature difference in the Northeast and use the alternating volume of water and ice to allow more juicy water to flow out of the cells and freeze a real frozen pear.

But we would like to remind you that the temperature in the south is relatively high, so it is not recommended to freeze pears in this way. Because pears will encounter high temperatures when thawing, once the thawing time is not controlled well, it is easy for the pears to deteriorate during the thawing process. In the end, your pear was indeed dark, but chances are, it was spoiled.

Some people also say that since the refrigerator temperature is not low enough, then using liquid nitrogen to make frozen pears, the temperature should be enough, right? What they did was: put pears in a pot and pour liquid nitrogen into them. But after soaking the pear in liquid nitrogen, maybe about half a minute later, we will hear a pleasant clicking sound – as the soaking time increases, the cracks in the pear will become more and more, and finally it will split directly into Lots of little pieces. The pulp inside will become more and more like a coconut in color. Two minutes later, after the liquid nitrogen has evaporated, we take out the “frozen pear” and find that it has become extremely hard. If we tap it on the table, it may make a loud banging sound, which is comparable to that of a brick. The skin of the pear is basically still yellow and has not changed much.

Therefore, liquid nitrogen is not suitable for making frozen pears. The temperature of liquid nitrogen is too low and will directly destroy the complete structure of pears. Put the frozen pears frozen in this way into water, and they will float on the water; after gradually warming up, the pears will become soft and rotten, because the pulp is directly exposed to the air and will be oxidized to brown, but it is no longer edible. .

But this also proves that the process of blackening frozen pears is a very slow enzymatic browning reaction. It is not enough to meet the low temperature conditions. It also takes a long enough time to convert as many phenolic substances into quinone substances as possible. Only then.

Interesting links

In the South, you may be able to make frozen sugar oranges

A brave experimenter replaced the pears with sugar oranges. After soaking them in liquid nitrogen, they found that the sugar oranges had also become hard and brittle, but because the outer skin was thicker and tougher, they did not crack and remained intact. After gradually warming up, the skin of the sugar orange becomes soft again. After peeling off the skin, the pulp inside looks like the original one, but when you bite it, it has a texture similar to that of a frozen pear, which is gritty, glutinous, and sweet. The degree will also be higher.

In other words, by using liquid nitrogen to quickly freeze sugar oranges, you can actually make delicious “frozen sugar oranges”! Because the peel protects the pulp relatively tightly, when it undergoes a physical change of reversible phase transition, most of the pulp can still return to its original state, but a small part of the tissue structure has been destroyed at extremely low temperatures. , so it can contribute to the final smoothie-like texture.

Therefore, if southerners want to eat frozen pears, they might as well try homemade frozen sugar oranges.

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