[[analysis-porterstem-tokenfilter]] === Porter Stem Token Filter A token filter of type `porter_stem` that transforms the token stream as per the Porter stemming algorithm. Note, the input to the stemming filter must already be in lower case, so you will need to use <> or <> farther down the Tokenizer chain in order for this to work properly!. For example, when using custom analyzer, make sure the `lowercase` filter comes before the `porter_stem` filter in the list of filters.