Short Jain answer:

1. What is “kanji”?

If you mean the fermented rice/flour drink (sour, kept for 1–2 days to ferment), then:

• It is fermented → countless new micro‑organisms are created.
• According to Jain aahar-niyam, fermented items are generally to be avoided, especially in Chaturmas, Paryushan/Das‑Lakshan, Aatham‑Chaudas, upvaas, etc. ( jainknowledge.com)

So, ideally a Jain should not drink such fermented kanji.

1. If by kanji you mean just freshly cooked grain water (for example, same‑day boiled rice water, not kept to ferment, used as a light food for weak digestion):

• Prepared fresh the same day.
• Not sour / not kept overnight / not bubbling/fermenting.
• Taken before sunset.

Then it can be treated like any other simple, non‑fermented Jain food and is generally acceptable for householders on ordinary days.

1. Practical guideline:

• If it’s sour, fizzy, or intentionally kept to ferment → avoid (more himsā due to fermentation).
• If it’s plain, same‑day boiled grain water for health/weakness → usually okay for a grihasthi Jain, but still best to keep it simple, fresh, and within daylight.

If you are following very strict niyam (Paryushan, Chaturmas rules, special vrats), then avoid all forms of kanji that even slightly ferment and prefer plain boiled water or very simple boiled food.