Celery extract contains a lot of nitrates and can be treated to produce nitrites as well [1]. The reason they use celery is to exploit a loophole in food labell

Celery extract contains a lot of nitrates and can be treated to produce nitrites as well [1]. The reason they use celery is to exploit a loophole in food labelling laws and avoid usage of the word nitrates due to their association with health risks. [1] https://en.wikipedia.org/wiki/Celery_powder https://en.wikipedia.org/wiki/Celery_powder