Inverted sugar syrup
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Inverted sugar syrup is sucrose-based syrup treated with the glycoside hydrolase enzyme invertase or an acid, which splits each sucrose molecule into one glucose and one fructose molecule. Although widely stated as providing a combination that is sweeter than sucrose, studies show that invert sugar has 85% the sweetness of sucrose. Invert sugar is more hygroscopic than sucrose, so it can be used to make a product that stays moist longer than if sucrose was used and is less prone to crystallization. This property is valued especially by bakers, who call the products trimoline or invert syrup.
The word invert comes from the way that sugar syrups rotate plane polarized light. A sucrose or glucose solution rotates light to the right, a fructose syrup rotates it strongly to the left. An equimolar solution of fructose and glucose inverts the rotation of light by rotating it to the left more than the sucrose syrup did to the right.
A familiar, household example of a product that is primarily invert syrup is honey. The process of making jam automatically produces invert sugar by combining the sugar with the acid in the fruit. Inversion can be partial as in products like Golden syrup or complete (100% conversion to glucose and fructose) depending on the functional properties required.
The inversion process is also used in fondant fills for chocolates. The enzyme is added but the filling is enrobed with chocolate before inversion has taken place while still very viscous. The filling then becomes less viscous with time.
Partially inverted sugar syrup can be home-made without the use of enzymes. When making a simple sugar syrup, add about one gram of organic acid, such as citric acid or ascorbic acid, per kilogram of sugar. Cream of tartar or fresh lemon juice can also be used instead. Boiling time needs to be extended to about 20 minutes. This preparation will hydrolyse enough of the sucrose to effectively prevent crystallization, without giving a noticeably sour taste. A way to make an invert sugar syrup without the use of acids or enzymes is to bring a mixture of two parts granulated sucrose and one part water to a boil and then reduce the heat to a low simmer for five to seven minutes until the solution becomes clear.
All these syrups, whether made from refined, raw or a mixture of both types of sugars are refined by the same process. An invert sugar is created by hydrolysing sugar (sucrose) to glucose (dextrose) and fructose. This is achieved by heating a sucrose solution, and applying either a solution of acid or enzymes. The syrup is neutralised when the desired level of inversion is reached.
Invert sugar has a lower water activity than that of sucrose, so inverts provide more powerful preserving qualities (shelf life).
The most popular is a partially inverted sugar such as golden syrup or refiners syrup, a mixture of 44% sucrose to 56% invert. This type of invert sugar offers high sweetness value of around 20% greater than sucrose.
The shelf life of partial inverts is approximately six months, depending on storage and climatic conditions.
Fully inverted sugar contains 95% invert to 5% sucrose. This type of sugar (high in invert) is used in bakery products that require moisture to be retained. As the sugars have been fully broken down into their constituents - sucrose, dextrose and fructose - they can be used in products that require fermentation. Full inverts also offer a higher sweetness value than partial inverts due to the higher solids content, which means they have the maximum preserving effect.
The shelf life is approximately two weeks, after which crystallisation can occur. They are microbiologically stable for a minimum of six months, depending on storage and climatic conditions.
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