Beetroot: not just a source of sugar

Month of publication: January-February 2012
Article Title: Beetroot: not just a source of sugar
Article author: Dr. Andreas Windt / Prof. Dr. Christa Hoffman
Translation and abstracts by: Translation from German by the 5th class B (German bilingualism component) Prof.sa Marina Gambacciani
Institute: Liceo "Tito Lucrezio Caro" - Cittadella

Until recently, beets were a valuable raw material - and in our areas the only - for the production of sugar. Therefore, both the efforts for their cultivation and the technologies for sowing and spreading their cultivation tended to this. But in the past years other qualities of this tuber have also been discovered. What are its new possibilities for use and how do they influence cultivation processes?

Until a few years ago, the beet was used exclusively for the production of sugar. The beets were cultivated and then transported to the sugar mills, at the end of the ripening process. There they were cleaned of residual and washed debris, and then obtained - through the processes of sugar extraction, purification of the juice, crystallization and centrifugation - the granulated sugar.
Recently, the benefits of this tuber with a thousand resources have been recognized - and not only by sugar producers - so that beets are now also used for other purposes.

Also the residual filaments and the calcium carbonate, which are obtained after the sugar extraction process, are precious raw materials; moreover, in recent times, beets are used for the production of biogas and bioethanol. In theory it is also possible to use foliage in biogas plants. The amount of dry mass of beet and its leaves is in fact far superior to that of corn. However, the use of the leaves is not particularly convenient at the moment due to their limited dry mass content, which makes transport expensive. Therefore, we will not deal with this aspect in the following.

Beets for the production of ethanol
With the adjustment of the sugar market regulation of 2006 there have been major changes with obvious repercussions on beet production: the related amendment has led to a reduction in sugar production of around 30%, following the closure of many sugar factories, and therefore a consequent decrease of the cultivated area. To compensate for this reduction and, at the same time, enter the renewable energy market, both Südzucker (with its subsidiary Cropenergies in Zeitz) and Nordzucker (with the subsidiary Fuel 21 in Klein Wanzleben) and Suiker Unie in Anklam have decided to enter the bioethanol production market. These three plants are the only ones in Germany to produce bioethanol from turnips. Since they have in common the being attached to a sugar refinery, one speaks of the so-called "attached facilities". For the refueling of these bioethanol plants throughout the country, more than 10,000 hectares of beet for the production of bioethanol have been grown since 2007. In most cases it is a cultivation established with a contract between the sugar industry and farmers. A part of the beets destined for ethanol plants are the so-called "excess beets", that is, beets that are above the established amount. The ethanol beets are not grown only in the area, for example, in the Klein Wanzleben sugar refinery, but also in the Nordzucker AG. For the principle of equivalence it is possible that bioethanol beets are used for the production of sugar and, in the same way, that the corresponding quantity of sugar beets is used for the production of ethanol.

... or for fermentation
Almost at the same time as the setting up of the ethanol production plants made from sugar beet, an experimental phase began for its use in biogas plants. Until then, corn had been used almost exclusively, as sugar beets were not considered suitable for the presence of earthy residues and debris. Moreover, their conservation is not as simple as that of corn. However, the experiences of using sugar beet in biogas plants are positive. Their short processing times proved to be particularly advantageous, resulting in increased methane production. Therefore today around 4500 hectares of sugar beet are grown in Germany for the production of biogas.
 

Cultivation methods
If sugar is produced from a beet, from another ethanol and from the third methane, one could suppose that a specific production process is required according to the different uses. And yet, in all three sectors, we work with a common goal: maximum yield of carbon hydrate and, consequently, of sugar per hectare. In fact, unlike wheat, where high protein content is an important quality indicator, nitrogen compounds in sugar beet are not welcome and also in other production sectors are not a priority objective. For sugar and ethanol production the sugar inside beet is used, for the production of biogas the dry mass is fermented, the quantity of which is strictly linked to the quantity of sugar.

Choice of beet varieties
In this way we also answer the question: which variety of beets is optimal for which process? The variety with the greatest amount of sugar is the best for every use, since it also obtains the greatest quantity of dry mass. It is quite indifferent, therefore, that the beet destined for the production of bioethanol is not treated in plants for bioethanol but in sugar factories. This also applies to turnips for the production of biogas, but with a small difference: while for both sugar and ethanol production, the internal quality of beet is particularly important, ie a low content of potassium, sodium and amino- N, this has no relevance whatsoever in beets intended for biogas production. Consequently, the quality level required for biogas beets is lower than for sugar beet. Experts in the field have frequently asked themselves the question whether it is perhaps better to use a fodder than a sugar beet for biogas production. However, the current results show that although the cultivation of fodder beet allows a quantitatively higher production of turnips, they, because of their low sugar content, produce less sugar than the others. Since autumn 2011, data on beet varieties of different origins that have been used for the production of biomass are available, so that the varieties for biogas production can also be chosen according to their environmental compatibility.

Fertilization and protection of plants
In fertilization, this applies in principle to the choice of varieties. The main objective is to obtain the maximum quantity of sugar per hectare, because in this way the highest crop of dry matter is reached. In sugar beets it has been known for many years that a moderate fertilization with nitrogen (amount of nitrogen from fertilizer and soil stock up to 160 kg / ha) produces higher quantities of sugar. The same is true for ethanol beets. In biogas beets, on the contrary, it has been thought for a long time that a higher fertilization with nitrogen leads to greater production. It is possible that this applies to the quantity of beet produced, but not to the amount of dry mass, as shown by the latest results from the Sugar Beet Research Institute: a fertilization of 100 kg / ha was more than sufficient for a satisfactory production of dry mass (and consequently of sugar). Only if the leaf is also to be used, fertilization with nitrogen can be increased slightly.
Also with regard to the protection of plants there are no significant variations with respect to the "normal" cultivation of sugar beets. Particular attention must be paid to an effective control of weeds and to timely fungicidal treatment.

The harvest
Even in the harvest, regardless of the subsequent use, the objective of obtaining maximum profit is worth. For the production of sugar and bioethanol it is necessary to avoid the waste of high quantities of beet, otherwise there would be a loss in the harvest.
Because the high production of molasses in beets decreases the sugar yield, the highest part of the beet and the foliage are not paid. Instead, in biogas beets, in which the internal quality is not particularly important (unlike those for the production of sugar and ethanol), the whole upper part of the turnip and even some leaves may be useful in the production process. When the top of the tuber is also harvested and used, the amount of solid mass of biogas beet can rise by 8%.

Synthesis
Thanks to its high profit potential and the many possibilities of use, sugar beet is a safe future crop. The growth of the harvest in recent years has also contributed to this. As for the production processes there is only a very slight difference between the crops destined for the production of sugar, bioethanol or biogas. A high amount of sugar is as important as a high amount of dry mass.