Where in the Spring Batch flow should I index an item?

I'm reading items from multiple flat files, processing them with some data validation steps, and writing them to Cassandra. Somewhere in the flow, I need to also send an index request to ElasticSearch. I'd like to use the ES Bulk API, so the index step should be batched to some degree.

My question is, should the Index step be an ItemProcessor, and ItemWriter, or something else entirely?