Like the shampoo which is a water-based homemade product, you should be able to preserve your DIY chamomile extract for around 1 week in the fridge. To optimize shelf life, make sure to use a sterilized container and to use distilled water. --- If you want to keep it for future shampoo batches, we recommend freezing the extract. If you want to use the extract on its own, you can add potassium sorbate to extend its shelf life to 6 months. Concentration is 2-3g per litre so for 300ml you can add 0.6g at the end of the process when your extract is done. This is if you use your chamomile extract on its own.