How to measure and analyse the texture of food, cosmetics, pharmaceuticals and adhesives.

Tuesday, 23 June 2015

Frozen Confectionery Texture: Sorbets and Ice Lollies

Sorbet ballsSorbet originally hails from the Roman Empire – and can be thought of as a low-calorie version of ice cream.
In the absence of non-fat milk solids, it usually consists of a fruit juice, plus carbohydrates stabilised with a hydrocolloid (e.g. alginate) and emulsified with mono- or diglyceride or polysorbate 80. The carbohydrates can be chosen so as to provide a harder or softer texture as in the case of ice cream, and aeration (overrun) can be obtained as with ice cream.

Sorbet is by definition an aerated frozen dessert, typically with a pH of 2.5 to 4.0 based on water, fruit juice or fruit juice concentrate, sugar, glucose syrup or other sugar types and combinations, functional systems blends, citric acid, flavourings and colourings. Sorbet does not contain fat, but may contain emulsifier and milk solids from whey powder if a creamy type of sorbet is to be produced.

Requirements regarding the texture of sorbet are very wide, ranging from a very fresh eating type with relatively large ice crystals to a creamy and warm eating type with comparatively fine ice crystals.

Several factors influence the consistency and texture of sorbet, including: product composition: total solids, sugar types and combinations, fruit juice/concentrate content and types and milk solids non-fat; Acidity/pH; Functional systems blend composition; Overrun; Processing.

The total solids mainly consist of sugar and other carbohydrates. These components have the greatest influence on the consistency of the end product. Fruit solids may form an important part of the total solids if substantial amounts of natural fruit are added to the sorbet base mix.  Depending on the nature of the fruit, fruit solids may have a significant impact on the body and texture of sorbet.  It is, for example, well known that mango fruit gives sorbet a body and texture which is different from that obtained with blackcurrant.

If the total solids content is too low, it will result in a hard, brittle sorbet. On the other hand, too many solids will make the product too soft, possibly leading to phase separation during storage and distribution. The same defect is also observed when large quantities of ingredients containing alcohol are added to the sorbet.

Due to the difference in the sugar types (e.g. dextrose, fructose, invert sugar, high fructose corn syrup, polyols) used with regard to their effect on solubility and the freezing point of the mix, they all have a varying influence on the texture in terms of brittleness or smoothness, fresh eating properties and flavour release of the sorbet. The final selection of the sugar combination to be used will depend on the scoopability, sweetness, and texture desired in the final product.

Sorbet does not normally contain any milk solids but, in some cases, whey powder is added to the sorbet mix in order to improve whipping properties and produce a sorbet with a creamier texture. Below are shown some comparative curves of sorbet and sorbet-coated ice cream bars.

Texture Analysis curves obtained from the 
penetration testing of 2 batches of sorbet-
coated ice cream bar
Texture Analysis curves obtained from the
penetration testing of 2 different brands
of sorbet

The final item in the directly consumable, frozen, ice cream style of product is the popsicle or ice lolly. The ice lolly has for a long time been the biggest selling moulded frozen food.  Here there is no question of aeration - the fruit-flavoured or fruit juice-containing sweetened drink is stabilised (if necessary) to avoid any settling out of suspended fruit cells or other fruit pulp materials and is frozen in moulds.  After freezing it may be coated, but as consumption is by sucking the item, rather than biting it, coating is not as satisfactory as in the case of coated ice cream.

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