Your reducer can emit a line without \t, or, in your case, just what you're calling the value. Unfortunately, hadoop streaming will interpret this as a key with a null value and automatically append a delimiter (\t by default) to the end of each line. You can change what this delimiter is but, when I played around with this, I could not get it to not append a delimiter. I don't remember the exact details but based on this (Hadoop: key and value are tab separated in the output file. how to do it semicolon-separated?) I think the property is mapred.textoutputformat.separator. My solution was to strip the \t at the end of each line as I pulled the file back:
hadoop fs -cat hadoopfile | perl -pe 's/\t$//' > destfile