Objective
- Evaluation of the fermentation of vacuum-sealed wet cake in big bags depending on the storage period
- Comparison of four different wet cake batches
- Measurement of fermentation losses via mass balancing
- Evaluation of the feed hygiene quality of wet cake
- Check of the aerobic stability of wet cake after opening the big Bags with different withdrawal quantities

Short version of the final report

Wet cake from bioethanol production from four different production batches was vacuum-packed using a new packaging technology in a PE bag in big bags and tested at the HBLFA Raumberg-Gumpenstein for feed and fermentation quality as well as aerobic stability over different storage times. During storage, which lasted up to 308 days from July 2016 to May 2017, a fermentation process with gas formation took place in all big bags, which led to a loss of vacuum in the plastic bag. As a result, the dimensional stability of the bales was partially lost. The four batches differed in crude protein content by up to 50 g/kg DM, but the dry matter (288 to 376 g/kg DM) and crude fat average values ​​(98 to 121 g/kg DM) also exhibited significant differences in some cases. Storing the wet cakes for ten months had no negative effects on the ingredient content. The acid formation caused by fermentation reduced the pH value of the wet cakes in the first few months of storage to the limit of the required stability. The desired lactic acid fermentation was only observed in the batch with the highest DM content. In the majority of the Big Bags an acetic acid fermentation took place with an average content of 24 g/kg DM. Butyric acid was formed in all wet cakes, meaning clostridial spores were present in the starting material and were actively involved in the fermentation process. In two big bags there was significant butyric acid fermentation and therefore incorrect fermentation. The breakdown of protein to ammonia was very low, as was the formation of ethanol by yeast fungi. As storage progressed, all wet cakes experienced a significant reduction in acidity, particularly acetic and propionic acid. The acid reduction only caused an increase in the pH value and a butyric acid-heavy fermentation acid pattern in one batch. A pH reduction was observed in two batches. According to the DLG assessment, the fermentation qualities of the wet cakes after 10 months of storage averaged 85 points (good) in one batch and the maximum point value of 100 (very good) in three batches. A slight discoloration and more or less pronounced microbiological colonization could be observed on the surface of the wet cakes. From a feed hygiene point of view, these discolored surface areas are not suitable for presentation to livestock and would have to be properly composted. After 10 months, the germ counts of all germ groups examined at the time of opening the silo were below the VDLUFA orientation values ​​for feed spoilage, ie feed hygiene was harmless for the germ groups examined. After four months of storage, no pathogenic germs (Clostridium perfringens, Listeria monocytogenes, Salmonella) were found in the wet cakes. Listeria moncytogenes was detected in the drier batch 4 after 10 months of storage. The background to the occurrence still needs to be clarified. The test of the aerobic storage stability of wet cakes stored for four months under air stress showed that when at least 5 cm were removed daily under cold conditions, there was good hygienic stability - regardless of the amount removed or acid treatment. Under higher air temperatures, there were clear differences in the yeast germ counts depending on the removal after 10 months of storage. The hygienic quality of Wet Cake could be ensured by removing 15 cm per day or treating the surface with propionic acid at a daily rate of 5 cm. At daytime temperatures above 15°C (period 7 to 19 hours), it is recommended to increase the daily removal amount to at least 15 cm or to treat the wet cake surface with diluted propionic acid (1:5) after each removal. In conclusion, it can be said that wet cake from bioethanol production was subject to certain qualitative fluctuations in terms of ingredients and fermentation process, but the feed hygiene safety and microbiological stability after opening the silo was largely guaranteed, even after 10 months of storage.