Delicious Science: how is jam made?
To make thick jam, you need enough pectin, as well as the right sugar and acid.
how is the jam made? break the fruit and boil it in a pot? It's not that simple! To get the perfect jam, you need the help of pectin, sugar and acidity.
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pectin is a kind of polysaccharides, which naturally exist in the cell wall and stroma of plants. The originally crisp fruit turns into a sticky lump in the process of cooking, which is the role of pectin. In the process of cooking, these pectin molecules will be released from the fruit, under the appropriate sugar and acidity conditions, long-chain pectin molecules will be combined by intermolecular interactions (hydrogen bonds, etc.) to form a gelatinous "network". When the jam is cool, this "network" can still net the moisture and maintain the gelatinous and thick texture.
(molecular structure of pectin)
different fruits have different pectin content, such as apples have higher pectin content, while strawberries have lower pectin content. If you use less pectin fruit to make jam, you need to add some fruit with high pectin content, or add some extra pectin to form a thick enough texture. The purified pectin is a widely used food additive, which is usually extracted from the peel of citrus fruit because it is rich in pectin.
in order to form a perfect jam, sugar and acidity are also important conditions. For jam, the appropriate sugar content (the final sugar content) is about 65.69%. Adding sugar certainly adjusts the taste, on the other hand, sugar also promotes the formation of gelatinous texture. Sugars such as sucrose and pectin molecules are hydrophilic, and if you want the pectin molecules to bind together, you need to "take away" the water molecules that bind to them. Hydrophilic small molecular sugars can play the role of "taking away" water.
acidity also has an important effect on the formation of jam, and the suitable pH of jam is about 2.83.3. There are acidic groups (carboxyl groups) in the molecules of pectin, which can avoid the dissociation of these groups and keep them in an electrically neutral molecular state, which can avoid the repulsion between pectin molecules because of electric charge. so that they can come together better.