Why does corn starch expire

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- Baking with yeast -

What is yeast

Yeasts are microscopic, unicellular fungi that can multiply quickly through cell division. In nature, yeasts thrive wherever carbohydrates (e.g. starch, sugar) are present and where alcohol and CO2 can be dismantled. The released energy is used by the yeast for their own metabolism. Today, only pure yeasts are used, which are sold in pressed or dried form. Yeasts are used in baking, wine and beer production, the food and pharmaceutical industries.

Processes during alcoholic fermentation

During alcoholic fermentation, the yeasts convert sugar (glucose) into alcohol and carbon dioxide (CO2) around.

C.6H12O6 --------> 2 C2H5OH + 2 CO2
1x sugar2x alcohol2x carbon dioxide

The above formula describes the process of alcoholic fermentation: You can see that under the action of yeast enzymes, 2 alcohol and 2 carbon dioxide molecules are formed from one sugar molecule. In addition to the two main products alcohol and CO2 there are many other by-products (e.g. glycerine, higher alcohols, succinic and acetic acid as well as many other acids), which are of minor importance in terms of quantity, but are crucial for the flavor formation in bread.

Fermentation when baking bread

The main ingredient in the flour used to make the dough is starch. Starch is a so-called "multiple sugar", i.e. the starch is a long (multiple branched) chain of individual sugar / glucose molecules. One starch molecule contains up to 1,000,000 sugar molecules.

These huge starch molecules have to be broken down into their components, the sugar molecules, in order for them to be usable by the yeast. This work is done by the yeast enzymes, which, like scissors, break the chains and separate the individual sugar molecules. Only then can the yeast use the sugar for fermentation.

Why does the dough "work"?

During the "rising" of the dough, the processes described above take place, that is: splitting of the starch chains and fermentation of the sugar molecules. This creates 2 molecules of carbon dioxide per sugar molecule, which accumulates in the dough as a gas in the form of microscopic bubbles. As the fermentation progresses, the amount of carbon dioxide in the dough increases steadily. This means that the amount of gas trapped in the dough increases. This creates the bubbles and bubbles in the dough that you are familiar with. The dough "rises" and experiences an increase in volume.

Influencing fermentation

The fermentation process is essentially influenced by 2 factors:

1. The temperature
Since fermentation is a chemical reaction, the intensity with which the reaction takes place can be influenced with the help of the temperature. In general: the higher the temperature, the faster the reaction takes place and vice versa. However, this rule has one restriction: the dough, and therefore the yeast, must never be exposed to a temperature higher than 40 during fermentation 0C lies. Above this temperature the protein of the yeasts coagulates, the yeasts die off immediately and the dough is "dead".

2. The duration
The longer the fermentation lasts, the more of the large starch molecules are broken down by the enzymes and the more carbon dioxide is produced in the dough. This rule also has a limitation: If fermentation lasts too long, too many starch molecules will be broken down into short pieces and the dough will lose the ability to hold the carbon dioxide in the dough. The carbon dioxide escapes from the dough, the dough collapses, it is said that the dough has "passed over".

Where does the "taste" come from?

Have you ever wondered how a bland-tasting dough is made into a great-tasting bread? The process that leads to the formation of the taste is known as the "Maillard reaction". In this reaction, which only occurs above 150-180 0C expires, the sugar molecules combine with the protein molecules of the flour. This reaction takes place wherever sugar and protein molecules are exposed to high temperatures, e.g. when roasting or grilling meat, roasting coffee or deep-frying.

During this reaction, on the one hand, dark pigments (the so-called melanoids) are formed, which are responsible for the color of the bread crust. At the same time, numerous fragrances and aromas are formed, which ultimately determine the taste of the bread. Since the Maillard reaction can take place most intensively in the outer layers of the bread during baking, this outer layer, the crust, is also the area of ​​the bread with the highest taste intensity.

tips and tricks

1. The pre-dough
In order to achieve a full aroma in the bread, it is good to leave the pre-dough to stand for a long time. A number of acids and flavorings are formed in the pre-dough, which positively influence the course of the Maillard reaction (and thus the taste of the finished bread). A standing time of the pre-dough of several hours can work wonders!

2. Sourdough from the last baking
Save a small amount of pre-dough left over from baking. To do this, rub about 2 tablespoons of pre-dough BEFORE kneading the dough with enough flour between your hands, so that a dry, crumbly mass is formed. Put them in a cup and keep covered in a dry and cool place until the next baking. Then simply dissolve with a little lukewarm water and then add directly to the next pre-dough (together with the yeast). Lactic acid is formed in the "sourdough" during its standing time, which in turn has a positive influence on the course of the Maillard reaction and thus on the taste of the finished bread.

3. Ingredients

  • Always use high-quality flours, because: "nothing comes from nothing"!
  • Be sparing with salt and yeast (1/2 cube per 1 kg of flour is sufficient), because: a good bread is characterized by its bread taste, not by the fact that it tastes salty or of yeast!
  • Experiment with the ingredients, because: "Trying is better than studying!"