Rye

1. Is there rye breeding just as there is wheat breeding?

Although some rye is grown and bred in the USA and Australia, 90% of all rye comes from Europe. Since t hybrid varieties were introduced around 1970 there has been tremendous progress in respect of higher yields and less dependence on soil characteristics.

2. What biochemical properties are characteristic of rye?

The very brief secondary dormancy of rye often results in signs of sprouting in the early stages of ripening. They are marked by increased enzymatic activity.

To a certain extent the role of the gluten in wheat is taken on by the pentosans in rye (content : 7-10%).

The insoluble part of the pentosans counts as dietary fibre. Rye starch consists of about 25% amylose and 75% amylopectin; the starch grains are mainly of the “B” type (diameter approximately 10 µm).

Medium-sized starch grains are now thought to have special technical functions in respect of shelf-life.

The baking properties of rye flours are determined largely by the ά-amylase formed during germination; its activity reaches a peak when the grain has a moisture content of about 30-40%.

This intensive enzymatic activity is also a reason for the widespread use of sour dough. The acidification restricts the activity of the enzymes.

3. How is rye assessed?

The following criteria are considered important : thousand grain weight (TGW), crude protein content, peak amylogram values for viscosity and temperature, and the Falling Number.

4. What are the most important test methods for determining the quality of rye?

The milling properties are determined in a standard milling test using a Buhler laboratory mill. Since 2002, both flour and meal have been used for testing the baking properties. The parameters determined are the amylogram, the Falling Number and the Rye Viscogram after Brummer. The tests should also include a baking trial.

5. What baking tests are used at present to evaluate rye?

Of the three standard baking tests for classified rye flours the one most often used for determining basic characteristics is the sour dough baking test that comes close to the real conditions at a bakery. There is also a yeast baking test without acidification and a lactic acid baking test in which acidification is achieved by adding a standardized amount of lactic acid depending on the mineral content of the rye flour. The most important parameters of the sour dough baking test are dough yield, dough properties, texture, elasticity of the crumb, purity of taste and the potential flavour resulting from the sour dough.

6. What is the rye Viscocity Test (RVT)?

The RVT is based on the swelling curve of the Amylogram. It uses a specific buffer and makes it possible to obtain, within 30-45 min, data that correlate with the baked volume of the bread. It can be used to optimize bread rye qualities for the market and serves as a selection criterion for rye breeders.

7. What problems are caused by the baking properties of rye flours?

The constituents of rye have a less compact chemical structure; by this we mean they are less resistant to breakdown by enzymes. Rye starch already gelatinizes at 55 ⁰C (wheat at about 65 ⁰C), and the proteins hydrolyze faster too. These disadvantages of rye have to be compensated for by measures on the part of the baker. For example, rye doughs have to be mixed more slowly in order not to destroy the protein structure.

No gluten is able to form in rye doughs because of their high pentosan content. The gas retention capacity of rye doughs is therefore much lower than that of wheat doughs. Moreover, the dough properties are not viscoelastic but plastic. Further problems are caused by wet dough surfaces and a tendency to stick to machinery and tools.

8. Why is acidification of the dough recommended when rye flours are used?

Rye doughs are nearly always made with acid (sour dough) in order to reduce the pH. Since the activity of alpha-amylases reaches a maximum at a pH of around 5.4 but is very low at 4.2, doughs with a reduced pH can easily be made up into rye bread without the products having a soggy, inelastic crumb. Such a negative change comes about through excessive degradation of the starch by the amylolytic enzymes during baking.

The reason for the high enzymatic activity of most rye flours is the shorter seed dormancy of rye. In many rye varieties warm, humid weather directly after ripening can trigger the germination process in the blade to fom a new plant. This process is termed sprouting. By lowering the pH it is possible to make bakery products with a long shelf life even from flour containing sprouted grain.

9. How I s good rye bread made?

Whereas efforts used to be directed mainly towards preventing sprout damage, this is now of secondary importance thanks to the development of suitable rye varieties and control of the baking processes on the basis of the Falling Number and the Amylogram. There is now a preference for Falling Numbers between 120 and 150 s, and multistage sour dough processes are still usual. But very acid conditions when a new sour dough starts to ferment inhibit the action of the enzymes. The main objective of all sour dough processes is now to form flavour components and their precursors in order to enhance the sensory properties of the bread. Working instructions are included.

10. Why is it so important to determine the gelatinization properties of rye flour?

Unlike wheat flour, rye flour contains very little structural gluten. In rye flour this skeletonforming function is performed by pentosans and starch. The Amylogram shows both the viscosity resulting from the two components and the gelatinization properties, especially the gelatinization temperature. As the gelatinization temperatures falls, the starch becomes increasingly susceptible to attack by amylases. Moreover, rye starch gelatinizes at a lower temperature than wheat starch. This means that amylases have greater significance than with wheat flour, where it is primarily the starch damaged by milling that is open to attack.

11. Is rye bread healthier than wheat bread?

Advantages can be concluded from the smaller need for pesticides and fertilizers for a constant yield, and less ability to host Fusarium; the toxin content is therefore lower. Furthermore, the protein is of higher value. On the other hand, rye and rye hybrids are susceptible to ergot.

12. Can the same milling line be used for wheat and rye?

In principle it is possible to mill rye on a wheat mill. The throughput will drop by about 50% and will be lower than on a comparable rye mill. The structure of the flour will also be different, namely coarser. Moreover, the flour colour tends to be less typical (with less greenish-blue sheen).