starch

STARCH

What is starch?

amylose1Starch belongs to a group of chemical compounds called carbohydrates. They are called this because they contain only carbon, hydrogen and oxygen. Pure dry starch is a white granular powder. Wheat flour contains 70-73% starch and most commonly anywhere between 8 -14.5% protein. If you look at flour under a microscope you can see lots of brick like structures called cells. In each cell you will see a granule of starch surrounded by glassy looking protein. Different types of starch have different structures. Potato starch is oval in shape, wheat starch is oval or round but smaller than potato starch, and maize starch has a “rocky” look.

Starch is called a complex carbohydrate because it is made up of many sugar molecules linked together. It has two main parts: amylose and amylopectin. Amylose is a straight or linear chain of sugar molecules linked together. Amylopectin is a branched chain of sugars.

amylose2Starch is a storage carbohydrate of plants such as cereals (wheat, maize, oats, rice and barley), tubers (potatoes, cassava and taro) and pulses (peas and beans). In whole wheat grains it makes up 60-70% of the grain. It is found in the endosperm which is the part of the grain that white flour is milled from.

Starch and the products derived from it are used in the food, brewing, pharmaceutical, paper, textile and adhesive industries.

In the food industry starch is used as a thickener, filler, binder and stabiliser in products such as soups, custard powders, pie fillings, sausages and processed meats, ice cream, sauces and gravies, baby foods, bakery products and baking powder.

The pharmaceutical industry use it in the manufacture of pills. It is used as a filler because it is bland and odourless. The textile industry uses starch for coating the fibre before weaving, and the dye pastes used for printing have starch in them. In the paper industry a starch solution is applied to surfaces of paper to increase the strength of the paper and give it a better finish. Starch also makes a very good adhesive or glue and is used to make cardboard cartons, boxes and containers. The gum used on the back of stamps and on envelope flaps is also made from starch.

Starch in Breadmaking and Baking

When starch is heated with water, granules absorb the water, and swell. Eventually they burst and the inner part of the granule spills out to form a thick gel. This is what occurs when you make a gravy or sauce. This process is called gelatinisation. In bread making not as much water is added as when making a sauce or gravy, and gelatinisation isn’t completed – the starch granules swell, and many don’t burst to form a gel. This forms a network of bloated starch granules all touching at the edges.

Starch also interacts with gluten during baking. The gluten breaks down and gives up water which is quickly taken up by the starch. This makes the gluten set and become rigid, which is why our loaves of bread don’t collapse when they come out of the oven.

gluten
This scanning electron microscopic view of dough rising shows gluten strands forming two ways, diagonally down and across the photograph. Starch and yeast granules can be seen randomly amongst the gluten. The smallest granules are yeast.

Starch also provides “food” for the yeast to feed on during fermentation. As explained, alpha- and beta-amylase work together to build starch into sugar. It is this sugar that feeds the yeast in fermentation. The yeast produces carbon dioxide which helps the bread dough rise and gives bread its finished texture.

Starch, gluten and the gas from yeast fermentation all work together to produce what we know as bread, with it’s crumb and gas bubble texture.

Starch is important for holding water in baked products like cakes. For certain cakes, cake flour treated with chlorine is used. The chlorine alters the starch’s properties and the baker can include more sugar and fat (like butter) in the recipe. A soft, low protein wheat flour is usually preferred as less starch damage occurs, which gives better volume and a softer crumb.

Biscuits are high in sugar and fat and low in moisture (water). These factors inhibit starch gelatinisation which therefore does little to contribute to the structure of a finished biscuit.

 

Handy Hint:
To freshen slightly stale bread simply reheat it for a short time in the oven. The starch granules reabsorb water, swell again and produce a “fresh” loaf. If the bread is very stale you could try pouring milk over it first.
Advertisements
Aside

REFLECTION JOURNAL NO.2

MIXING METHODS

  For the past week, we spend much more time in lab, from baking quick breads and cookies we learned 4 type of mixing methods, they are one-stage method, muffin method; creaming method and biscuit method.

  one-stage method . it is the same to the all-in stage method ,  it means put all ingredients together, then mixing use the paddle in low speed. , we always use this method to bake cookie, because cookie doesn’t need too much gluten developed,   We’ve made coconut macaroons in one-stage method, this way is easier than other ways; we don’t need to separate ingredients to different bowls, so that we can save time and get uniform dough, but, in one-stage method, cause we put all ingredients combined at once, so it is not easy to control over mixing.images-1

  Muffin method. We usually use this method for quick breads which quick and easy to make. First of all, we need to separate ingredients to two parts, one is dry, like flour, baking soda, salt, and one is wet, like oil, water and yogurt. For example, when we made carrot zucchini muffin, we whisked every wet stuff together, including liquid oil, eggs, after that we whisked all dry stuff, then we putted all wet ingredients to dry one, used the spatula to stir, until the flour moistened and no lump, finally, we got perfect muffins. So, muffin method also is easy and fast way to bake, another benefit is we can storage wet and dry parts separately, when you want to have some delicious muffins to treat your gust, just combine them, it is faster than you thought.  In this way we still don’t need too much gluten development, we all know that enough mix can develop the gluten, so, the disadvantage of muffin method is the dough can become over mixed quickly.

carrot-zucchini-muffins-prep

  The creaming method is place(solid fat) butter and sugar in mixer, use the paddle in the second speed, you can’t exactly judge it which is done or not by the time, but from observe and feel, you must know it. When the cream becomes light and fluffy, then add the eggs one by one, creaming after each, after all the liquid stuff in, stir dry ingredients, and combine all ingredients together. There are two advantages of creaming method, it makes fat and sugar dispersed well, gives muffins nice crumb, and less danger of over mixing. but this method may spent more time than others. Last week we baked banana walnut muffins in creaming method, we spend long time and paid more patience, but it is worth doing. DSC05044

  Biscuit method has another name— pastry method, cause it incorporates the same technique for mixing pie dough, in this method, don’t need to melt or mix butter, just cut cold butter to small cubes into the flour, lastly add the liquids. When biscuits by heated, the butter melts, the water steams, your biscuits rise and got flaky layers. In this way, the advantage is don’t need mixer to mix, so, no worry about over mixing, in addition, there are not too much stages, it is fast to bake. Oppositely, the disadvantage is you have to scale all ingredients accurately, actually, the week before last, Ms. Fionna was give us a experiment to show a little bit different leaven agents, different weight must cause big different result.              leavening2_t

scones_intro1_1989462b

   These four mixing methods, they are all have advantages and disadvantages, if let me choose one over the other, it depends these questions: what will I bake? how many time do I have? what kind of ingredients do I have? who will eat it? and so on. It doesn’t make sense if someone just choose one method for every baking goods. whatever use which method to mixing, all have to bear in mind these details: scrap bowl after used, avoid waste! keep everything clean and tidy, it shows your organization well or bad!follow the instruction! be teamwork, try to get along with different people.