Processing methods

Processing

Rye grain picked straight from the field does not fulfill all the criteria that we have set for human food but through processing it can be transformed into variety of tasteful and health promoting products. Different processing methods affect the structure, taste and nutritional value of rye products.
Different rye varieties and yields may have different properties. For processing the most important property is the falling number. Falling number is an indicator of the germination phase and enzyme activity of rye, which decides to which use the rye yield can be utilized. The higher the number, the lower the enzyme activity. When the falling number is low, the rye is better for malting. A higher falling number yield of rye can be used in bread baking.

Milling

Different milling fractions of rye are used to different purposes. Whole grain flour, where no layers of grain are removed, is the richest in nutrients and a very good source of fibre (20-25 % of dry matter). The bran of the grain can be removed partially or totally and it can be used separately. Most of the rye fibre is located in the bran section. Therefore in flours without bran (endosperm rye flour) the fibre content is reduced, although compared to for example wheat the reduction is more moderate, endosperm rye flour still being a relatively good source of fibre (10-12 % of dry matter).

Germinating

The grains can be germinated to produce malt, which then can be used in baking or production of beverages like beer or whiskey. Germination causes starch breakdown in the grain and it can possibly affect the amount of phenolic compounds and folate in rye grain.

Fermentation

Fermentation e.g. sourdough baking is a common process when making rye bread. Fermentation is based on lactic acid bacteria, which can be produced via a starter or yeast added to the dough. A starter is a small amount of old rye sourdough that is first dissolved into a small amount of water and rye flour, and then left to ferment for several hours before adding the rest of the ingredients.

Fermentation decreases the pH-level of dough and it produces the sour taste of a typical rye bread. Fermenting changes the structure of rye and it slows down the enzyme activity of the dough. Fermentation can increase the shelf life of rye products and improve the structure. On top of that it is possible that fermentation can fortify the usability of some minerals and bioactive compounds of rye.

Fermentation with a specific type of sourdough can reduce the FODMAP (fermentable oligo-, di- and monosaccharides) content of rye bread. FODMAPs are carbohydrates that can be fermented in the bowel and therefore they can cause inconvenient symptoms especially for ones suffering from irritable bowel syndrome (IBS). Recently a low-FODMAP (fermentable oligo-, di- and monosaccharides) rye bread has been developed and it has been shown to relieve the symptoms of IBS patients.

Cooking

Cooking is usually the last step of process when making grain products. Cooking makes the products more pleasant to eat and easier for us to digest. During rye bread making the heat causes the starch granules to leak, which leads to formation of resistant starch. This together with the ryes protein composition gives rye bread its typical tender and compact structure. The structure is possibly one reason behind the lowered postprandial insulin response and increased satiety after rye based meal.

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