The smooth coolness of a gelatin salad contrasts pleasingly with the various ingredients that commonly are molded in it. However, the desired final effect relies on good preparation techniques. If using unflavored gelatin, be sure to hydrate it by soaking it briefly in cold water (1/4 cup water per tablespoon gelatin) as a preliminary step. Its coarse particles take up water less readily than do the finer particles used in flavored gelatins.
A critical part of preparing a gelatin salad is the complete dispersion of the gelatin. A measured amount of boiling liquid, usually water or a fruit juice, is poured over either flavored or hydrated unflavored gelatin to begin the process of dispersion. Slow stirring is needed to facilitate the solution of the gelatin particles, and this should be continued until absolutely no particles can be seen. In particular, stirring needs to be directed toward scraping all gelatin particles from the bottom of the container, where they tend to settle. Unless this is done, an undesirable rubbery layer may form.
When the gelatin has been dissolved completely, the remainder of the liquid specified in the recipe is stirred into the gelatin dispersion. This portion of the liquid may be cold liquid or even ice cubes. The use of ice speeds the cooling of the dispersion and quickly initiates
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formation of the gelatin gel structure. It is necessary to stir while the ice cubes are meltingso that the concentration of gelatin is uniform throughout the mixture and the entire disper- sion is cooled at the same rate. If stirring is not done, the regions adjacent to the melting ice will begin to set and contribute a lumpy texture in the finished product. With steady stirring throughout the cooling gelatin, gelation will begin to occur rather slowly. The first sign is the development of a syrupy consistency. Any remaining ice should be removed at this point and fruit or other ingredients stirred in until distributed. This mixture then is refrigerated in a bowl or mold until gelled.
Recipes for gelatin salads are based on proportions known to produce the desired consis- tency, so that the salad can be served easily without softening. Careless measurements of liquid can affect results; too much liquid produces too soft a product, while too little creates a rubbery texture. When canned fruits are not drained thoroughly, their extra liquid weakens the gel structure. If desired, the drained juice can be used in making the gelatin if this juice is treated as part of the liquid in the recipe.
Most fresh fruits can be added to gelatin salads to add texture, flavor, and color. However, fresh or frozen pineapple and fresh papayas and kiwi fruit cannot be used because enzymes in them react with the gelatin proteins. The result is breakdown of the gelatin gel and creation of a sol that can only be served as a soup.
gel Colloidal system in which a solid forms the continuous phase and a liquid is the discontinuous phase.
sol Colloidal system in which the discontinuous phase is a solid and the continuous phase is a liquid.
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—Recipes using gelatin.
sCIenCe note
GElATIN GElS
A dispersion of gelatin is a colloidal dispersion, in which gelatin molecules are the solid. If gelatin (the solid) is dispersed uniformly in a liquid, the dispersion is classified as a sol. A sol is a colloidal system in which the solid is dispersed in a liquid; that is, the solid is termed the discontinuous phase and the liquid is the continuous phase. In other words, in a sol, it is possible to get from one gelatin molecule to another only by passing through the liquid in which it is dispersed. This is the colloidal system being formed when gelatin is being dis- persed in boiling liquid in preparing a gelatin salad.
When a gelatin sol begins to cool, the gelatin molecules gradually move slower and slower through the liquid. These fibrous molecules begin to bump against each other and occasionally form hydrogen bonds between mol- ecules. The cooler the system gets, the more slowly the protein molecules move, and the greater is the likelihood of hydrogen bonds beginning to hold one gelatin molecule close to another one. Gradually, many molecules are cross-linked by hydrogen bonding into a jumbled network in which water becomes trapped. Finally, the gelatin molecules form a continuous network, and the water is trapped in discontinuous pockets within this network. In short, the colloidal system has undergone a transition from the original sol to a different colloidal system, that of a gel. A gel no longer exhibits the flow properties characteristic of a sol. This makes it possible to mold gelatin and serve it in a defined shape.
The ease with which gelatin molecules can cross-link to each other to establish the gel structure is influenced by the pH of the dispersion. The addition of some acid to help bring the system to a pH of 5 makes it easy for the gel
to form because this is the isoelectric point of gelatin. At this pH, there will be a minimum electrical charge on each molecule. This lack of electrical charge on the surface helps to keep similarly charged molecules from repelling each other. When molecules can get close together, hydrogen bonds are able to form comparatively easily. If the system is acidified (with lemon juice or other edible acid) to a pH lower than 5 or is more alkaline than 5, it still is possible for hydrogen bonds to form between gelatin molecules and establish a gel. However, this occurs more slowly and produces a gel with somewhat less strength than one at a pH of 5.
The amount of gelatin in a product clearly influences the strength of the gel, for there will be fewer molecules to link by hydrogen bonds and form the continuous net- work when the gelatin concentration is low than when it is high. A low concentration of gelatin forms a weak gel or may even not gel at all. On the other hand, too high a con- centration of gelatin gives such a dense network that the gelatin gel is too tough to be enjoyed. A ratio of a table- spoon of unflavored gelatin per cup of liquid produces a good gel.
If sugar is increased in a gelatin recipe, the gel will be more tender than the original product. In fact, a very large increase can even prevent gelation. The effect is attributed to the reduction in the concentration of protein when sugar is increased.
Gels look like solids, but actually they are undergoing continual change during storage. Evidence of this is the difficulty of trying to serve a gelatin product that has been firm for only an hour versus one that has been chilled for six (Continued)