How are the frozen pears in Northeast China frozen?

Review expert: Wang Guoyi, Postdoctoral Fellow in Nutrition and Food Safety, China Agricultural University

The heavy snow season is approaching, and the recent sudden drop in temperature has caught everyone off guard.

When talking about cold weather, one cannot avoid talking about the Northeast. And every winter, a mysterious fruit that Northeastern friends love to eat becomes the focus of curiosity among netizens across the country: that is, after dinner, Northeastern people take a basin of cold water with a few black fruits soaked in it - frozen pears .

Source: A shopping website

Looking at the dark fruit, I believe everyone can't help but wonder: How can there be black pears in the world? Is it rotten? How did it happen?

Origin of frozen pears

After November, the overall temperature in Northeast China will drop to zero degrees or even lower. The temperature will not rise again until March or April of the following year.

Such a long winter has turned the Northeast region, including the eastern part of Inner Mongolia, into a natural "refrigerator" . In such an environment, food is naturally not easy to rot and spoil, so the people here have the custom of "eating ice and snow". Typical representatives include candied haws, frozen persimmons, and frozen pears.

Source of frozen persimmons丨Baidu Encyclopedia

Compared with candied haws, which requires certain modern technology, frozen pears have a longer history. As early as more than a thousand years ago, the Khitan people of the Liao Dynasty had the habit of eating frozen pears. Pang Yuanying of the Northern Song Dynasty recorded in "Wenchang Miscellaneous Records" that "I was sent to the northern Liao Dynasty and arrived at Songziling... I pressed sand pears, which were frozen and inedible... I soaked them in cold water for a long time, and the ice was all on the outside. After a while, I knocked it off and the pears were melted."

At that time, after the Khitan people harvested the fruits in autumn, they placed them outdoors and covered them with snow. They would take them out to thaw and eat them when needed. In addition, Huang Tingjian and other literati also described frozen pears, which is enough to show that the custom of eating frozen pears appeared as early as the Liao and Song dynasties . In addition, there are also records about frozen pears in Gansu, Qinghai, Ningxia and other places in the northwest.

How do pears become frozen pears?

The temperature in different regions is not exactly the same, so the production methods are slightly different. Take Heilongjiang Province as an example. Generally, late-ripening pear varieties that mature in late September to early October are selected. After picking, they are packed into cartons or plastic baskets and stored in a shaded shed or well-ventilated room. Some people also directly lay plastic sheets on the ground and place them directly on them, or store them in piles. When the temperature drops in winter, they freeze naturally.

Source: Wang Yang, Wang Wenhui, Tong Wei, et al. Analysis of frozen pear quality based on color, aroma, taste and texture[J]. Chinese Journal of Agricultural Sciences

During the freezing process, the aroma components, sugar components, organic acid components, texture and other characteristics of the pear will change. The above picture shows three kinds of frozen pears with good quality, from left to right: frozen Nanguo pear, frozen Jianba pear, and frozen Huagai pear. Related research shows that after frozen storage, the aroma of the three kinds of frozen pears becomes lighter, the content of monosaccharides and monoacid components changes, but there is no significant difference in total sugar content, and the total acid content shows a downward trend, which is particularly obvious for frozen Huagai pear and frozen Jianba pear.

Source: Baidu Encyclopedia

During the freezing process, the cell structure of the frozen pear is destroyed, and the polyphenol oxidase in the cells combines with oxygen, which causes enzymatic browning to form colored substances. This is why the frozen pear's skin is black. After freezing, the hardness of the frozen pear is greatly reduced, and the flesh becomes pulp. You can chew it, or you can bite a hole and suck it, which is also friendly to the elderly.

How to thaw frozen pears?

In the Northeast, frozen pears are usually soaked in cold water or thawed directly at room temperature. Now they can also be thawed in a microwave.

People generally call the method of thawing with cold water "de-freezing". Since the freezing point of frozen pear flesh is below zero degrees, a thin layer of ice will form on the surface of the frozen pear during the "de-freezing" process. When it is completely thawed, you can break it with a spoon and eat it. The process of breaking the ice shell is also an interesting thing when eating frozen pears.

Source: A shopping website

The Northeast region is in the cold winter around the Spring Festival, so it is inevitable to have a lot of fish and meat in the diet. Eating a frozen pear after the meal not only has the effect of sobering up and relieving greasiness, but also has the effect of clearing away heat, relieving sore throat, relieving cough and relieving asthma.

Of course, eating more frozen pears is not necessarily better. For example, people with weak spleen and stomach or diabetes should control their intake. The above content is recorded in Li Shizhen's Compendium of Materia Medica and many folk historical stories.

Relevant research shows that from the perspective of modern science, frozen pears made from Pitko (autumn pear) contain a variety of nutrients such as amino acids, minerals, vitamins, etc., with a rich variety and reasonable proportions. Frozen pears have also been recognized in the field of modern science.

Source: Baidu Encyclopedia

Although frozen pears have so many good effects, their sales are not optimistic. Due to the lack of unified standards and systematic guidance, the quality of frozen pears produced by different farmers varies. In addition, the sales channels are basically very simple (farmers' markets, street vendors), and there is a lack of popular science information. People who don't know frozen pears often mistake them for rotten pears. This situation is regrettable.

It is now winter, and the highest temperature in Beijing has dropped to near zero degrees. It is the right time to taste frozen pears. If you are interested in this "legendary northern fruit", you might as well enjoy a cold and sweet frozen pear in a warm house while enjoying the snow scene.