It is a very small single cell micro-organism. Enzymes are proteins which catalyse, or speed up, biological reactions. Enzymes usually have an -ase suffix, eg. Biological reactions are the reactions that occur in living things.
For example, when we eat food we need to digest it. Without enzymes in our bodies, digestion could take weeks instead of a matter of hours. Enzymes are specific for a certain reaction, for example, the enzyme lactase will only work in reactions where the chemical lactose is present. This is like a jigsaw puzzle where only certain pieces fit together. Enzymes also have temperatures and pH levels which are optimum for them.
The whole process looks like this:. Enzyme digestion of starch can occur in two main ways by damaging starch mechanically, or by gelatinising it. Damaged starch sounds as if it has been ruined for baking, but this is not true. It simply means that some starch granules have been crushed, broken or chipped during the milling process.
Several enzymes are required in dough to convert starch into simple sugars that yeast can feed on. This is a complex process and involves the enzymes alpha and beta amylase. If these enzymes are present they can digest starch and provide the sugars for yeast fermentation. Starch exists in two different forms — an unbranched chain form called amylose and a branched form called amylopectin. Enzymes that digest starch are called amylases.
There are two importaint enzymes that digest these types of starch alpha-amylase and beta-amylase. Dough must contain some alpha-amylase to digest the amylopectin part of starch, but if dough contains too much of this enzyme it can completely liquify starch. Alpha-amylase attacks starch practically anywhere along its chains, producing smaller chains of various lengths. These chains can contain one unit glucose , two units maltose or larger units called dextrins that contain many glucose units.
In a dough, beta-amylase can then digest these dextrins into maltose. Cereal grains and flour always have an adequate supply of beta-amylase that can digest amylose completely into sugars. Beta-amylase attacks amylose chains and breaks them into molecules of maltose. Maltose is a disaccharide containing two glucose molecules.
Beta-amylase will also start digesting amylopectin from one end of the molecule but it cannot break the branches so digestion stops whenever it comes to a branch. Therefore, beta-amylase digestion of starch results in a mixture of maltose and larger dextrins. Yeast produces the enzyme maltase to break maltose into glucose molecules that it can ferment.
Once the starch has been broken down into these simple sugars, other enzymes in yeast act upon simple sugars to produce alcohol and carbon dioxide in the bread making step called fermentation. The yeast enzyme, zymase, then ferments these sugars. Diagrams Starch belongs to a group of chemical compounds called carbohydrates. They are called this because they contain only carbon, hydrogen and oxygen. 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.
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. 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.
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.
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 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. As explained, alpha- and beta-amylase work together to build starch into sugar. It is this sugar that feeds the yeast in fermentation.
This is cream yeast. Instead, it is directly transported to bakeries. Next, the yeast is concentrated even further. Manufacturers can using vacuum drying equipment for this for instance. By pressing this together into blocks, it makes what you would consider fresh yeast.
Fresh yeast is sold at bakeries and some supermarkets. It is less active than cream yeast, but it still has to be stored in the fridge to keep it alive for long enough. Depending on the yeast type the total shelf life is only about 4 weeks. Since that is generally still not dry enough, the yeast is next dried even further.
A way to do this is using granulator and air drier. This yeast is still very active and stored in the freezer to ensure it stays active for sufficiently long. Drying the yeast even further gives dried yeast. The yeast is dried into tiny granules and you can scoop it from the cup quite easily. This yeast can generally be stored for up to two years at room temperature.
This type of yeast is no longer active and alive. It has been deactivated on purpose. As such, you cannot use it for proofing breads, etc. Instead, you use nutritional yeast to add flavour to your food. It provides depth by adding umami to your food. Your options are either fresh or dried yeast. Fresh yeast will work fine, however, it only lasts a few weeks in the fridge.
For most recipes you can exchange fresh and dried yeast. Keep in mind that fresh yeast contains a lot more water than dried yeast. Therefore you need a lot more fresh yeast. As a rule of thumb, use three times the amount of fresh yeast as you would of dried or follow the guidelines in your recipe or on your yeast package.
When using dried yeast, there is another choice to make. There are several types to choose from. In the US the most common ones are active dry, instant and rapid rise or a similar name, these are generally brand names. Outside of the US, instant yeast is most common. By reading the instructions on how to use your yeast and the guide below, you should be able to tell which of the three it is. Active dry yeast needs to be activated before you can use it. You do this by dissolving some of it in luke warm water.
The major reason for rehydrating active yeast is its large granule size. Those large pieces make it harder for the yeast to fully rehydrate and absorb enough water. By placing it in some water in advance, it easy access to enough moisture. Active dry yeast is less stable than more modern varieties. As such, proofing the yeast on forehand is a good test to see whether it still is sufficiently active. Even though this is the general advice given when using active dry yeast, several of the current active dry yeast varieties work perfectly fine without any pre-hydration.
You can use them in the same way as you would instant yeast. Over the years drying technologies for yeast have improved a lot. This is what enabled the production of instant yeast. It is similar to active dry yeast, however, it does not have to be activated on forehand. Instead, you can just add it to the rest of your ingredients. Yeasts all have their own ideal growing conditions. It is why you might find different types of instant yeasts being sold.
Generally speaking, only specialized online stores have these varieties in stock. When scaling up having different types of yeast may be helpful. At a small scale you can often fix the issue by extending leavening time or adding more yeast. An even more recent development is that of Rapidrise or Quickrise yeasts. These yeasts are very active, as the name says. As such, they can rise a product pretty quickly, but, they really only work well for one rise.
Save my name, email, and website in this browser for the next time I comment. Notify me via e-mail if anyone answers my comment. This site uses Akismet to reduce spam. Learn how your comment data is processed. There are inconsistencies in the temperature s in these article s. At times you state water should be FF for proofing in other articles you say FF. Other articles you state yeasts dies at F in this one says F. All Rights Reserved. Design by Purr. What is Yeast? Yeast for Baking Yeast that is used for baking is in three forms: natural yeast, fresh yeast, and dry yeast.
Fresh Cake Yeast Fresh yeast is a commercial product that is a moist cake form of yeast cells that are in an active state as opposed to a dormant state as dry yeast cells are.
Dry Yeast Dry yeast are yeast cells that have been dried out to put them in a dormant state. How Does Yeast Work in Baking? Baking Recipes Using Yeast You Might Enjoy Gaining confidence in working with yeast opens up a whole world of recipes to make from scratch! Leave a Reply Cancel reply Your email address will not be published. Eloicito — April 22, pm Reply. Dorsinia Cason — May 22, pm Reply.
0コメント