var checked= model.DoneErrorMeterEntrySerialnumbers;
                    var workingList = new List<iem_exampleList>();
                    workingList.Add(new iem_exampleList());
                    foreach (var example in checked)
                    {                       
                        if (!String.IsNullOrEmpty(meter))
                        {
                            var addItem = db.iem_exampleList.Where(x => x.serialnumber == example).FirstOrDefault();
                            addItem.processing = addItem.processing + "\n";
                            workingList.Add(addItem);
                        }
                    }
                    string filePath = @"beispielPath\beispiel.csv"; 
                    using (var writer = new StreamWriter(filePath))
                    using (var csv = new CsvWriter(writer, CultureInfo.InvariantCulture))
                    {                        
                        var header = new classForHeader();
                        csv.Configuration.Delimiter = ";";  
                        csv.WriteRecord<classForHeader>(header);
                        csv.WriteRecords(workingList);
                        
                    }

Encoding.GetEncoding(850)                     // MS-DOS ASCII Zeichensatz
Encoding.GetEncoding(1252)                   // Windows ANSI Zeichensatz
Encoding.UTF8                               // Universeller Zeichensatz, Standard bei .NET

 using (StreamWriter sw = new StreamWriter(file, false, Encoding.UTF8)) ...