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Tapioca: Tapioca pearls, significant physical properties, unique mouthfeel, bubble tea.

The Tapioca wikipedia page has some general information about how tapioca is made and how it differs in different regions of the world. There is not much information on the physical and molecular properties of the plant from which tapioca is made (cassava) and how they change during processing to produce the characteristics of tapioca. I also want to focus on the specific attributions and applications of tapioca pearls, one of the most common forms of tapioca.

Wiki Edit:

Processing of the cassava flour into tapioca pearls requires the intermediate step of a product called tapioca grit. Tapioca grit is dried cassava flour that is partially gelatinized so that it looks like flakes or irregularly-shaped granules. Traditionally, moist starch flour is roasted on an open firewood flame in a shallow stainless steel pan at 120 - 150°C with constant stirring for about 20 minutes. To prevent sticking and burning, the pan is rubbed with vegetable oil before roasting. Another method of roasting is with the rotary dryer method where the moist starch flour is roasted in an electrically powered rotary dryer, heated with charcoal. In this method, the flour is roasted at 100°C for 20 minutes. This method also includes a fan that removes steam during the first 10 minutes of roasting, allowing the flour to partially gelatinize in the last 10 minutes. Afterwards, the fan is again operated to dry the starch particles.

In contrast, making starch pearls uses a different process of roasting. To form the pearls, the tapioca grit can be cut or extruded into the shape of pearls, either small (3mm) or large (6-8mm). The pearls are subjected to a form of heat-moisture treatment, which heats the starch at a high temperature, usually above the gelatinization temperature (>100°C), at a very limited moisture content to avoid gelatinization (18-30%). According to these guidelines, starch pearls are roasted at temperatures of 120 to 180°C for 8 to 10 min in open pans. In order to make these pearls marketable throughout the world, it is also important to consider additional processing steps to lengthen its shelf life. Freshly made wet starch pearls have a shelf life of only about 10 days at refrigerated temperature. One method that has proved effective in maintaining the stability of the pearls is to dry them until further use. Dried starch pearls have an enormously extended shelf life of up to 2 years. 

The importance of the starch content of tapioca is seen in the effect of starch properties on the composition of the tapioca pearls. Amylopectin, one of the polysaccharides that form the structure of plant starch, is found in different chain lengths throughout the varieties of cassava roots. The length of the chains correspond to the degree of polymerization of the molecule, and are classified into A chains, B1 chains, B2 chains, and B3+ chains, which increase in chain length respectively. Cassava starch is shown to have more long chain length and fewer short chain length amylopectin than potato starch. A higher proportion of B2 and B3+ chains to A chains is associated with a higher gelatinization temperature and pasting temperature. This can be explained by the correlation between a greater number of branched chains and a greater density of the amylopectin molecule. Thus, an amylopectin molecule that contained a greater percentage of B3+ chains, which have the highest degree of polymerization, will not only have more chains but will be more densely packed, having a larger molecular weight. A larger molecular weight also indicates that the molecules do not dissolve as easily in water. This may be undesirable for making certain food products that require water solubility, but the inter and intra-molecular interactions that are possible through the long chains of the amylopectin molecules contribute to important properties that affect tapioca pearls.

Tapioca pearls have many unique properties that contribute to its interesting texture and mouthfeel. Many of these physical properties are a result of its starch composition and are significantly affected by processing. Tapioca pearls are characteristically soft and chewy, with a prominent elastic texture and translucent appearance. This texture is cultivated throughout the process of making the pearls. The heat-moisture treatment during the formation of the tapioca pearls controls the amount of water present as well as the degree of gelatinization. In the moist heat, the starch readily absorbs water and solubilizes, maintaining the swollen structure of the pearl. When a critical temperature is reached, which is usually characteristic of a particular starch, it undergoes gelatinization, an irreversible process. In this process, the starch granules absorb the surrounding water and are able to swell to many times their original size. Even with limited moisture, as in the heat-moisture treatment, the pearls are able to swell effectively because of the naturally occurring “free-swelling” starch from the cassava root. The amylose molecules in the starch are believed to create a network of micelles between and within the starch particles, helping to prevent the disintegration of the pearl during cooking. The final product is 50% gelatinized and sets as a gelled particle.

Gelatin Dessert: Chemistry [edit]

Collagen is a protein made up of three strands of polypeptide chains that form in a helical structure. To make a gelatin dessert, such as Jello, the collagen is mixed with water and heated, disrupting the bonds that hold the three stands of polypeptides together. As the gelatin cools, these bonds try to reform in the same structure as before, but now with small bubbles of liquid in between. This gives gelatin its semisolid, gel-like texture.

Physical properties: Because gelatin is a protein that contains both acid an base amino groups, it acts as an amphoteric molecule, displaying both acidic and basic properties. This allows it to react with different compounds, such as sugars and other food additives. These interactions give gelatin a versatile nature in the roles that it plays in different foods. It can stabilize foams in foods such as marshmallows, it can help maintain small ice crystals in ice cream, and it can even serve as an emulsifier for foods like toffee and margarine.

Equation: The Bloom Strength of a gelatin mixture is the measure of how strong it is. It is defined by the force in grams required to press a 12.5 mm diameter plunger 4 mm into 112 g of a standard 6.67% w/v gelatin gel at 10°C. The Bloom Strength of a gel is useful to know when determining the possibility of substituting a gelatin of one Bloom Strength for a gelatin of another. One can use the following equation:

C x B^½ = k 

or      C₁(B₁)^½÷(B₂)^½ = C₂

Where C = concentration, B = Bloom strength and k = constant. For example, when making gummies, it's important to know that a 250 Bloom gelatin has a much shorter (more thick) texture than a 180 Bloom gelatin.