The general rule is simple: raw plant matter that has not been cooked, salted, oiled or processed. Everything else is a variation on that rule.
Good scraps
- Citrus peels — orange, lemon, lime, grapefruit, mandarin. The classic choice. Gives the finished liquid its characteristic clean smell.
- Apple and pear cores, stems and skins.
- Pineapple skin and core. High in enzymes; a small amount goes a long way.
- Papaya, mango, guava skins.
- Vegetable trimmings: carrot tops, celery ends, onion skins in moderation, leek greens.
- Leafy trimmings: outer cabbage leaves, lettuce ends, herb stems.
- Cucumber and zucchini ends, tomato tops (small amounts).
A mix of two or three fruit types usually gives the best-smelling finished liquid. All-citrus batches are the most forgiving for beginners.
Avoid
- Cooked food of any kind. Cooking changes the sugars and proteins in ways that favour spoilage microbes.
- Meat, fish, dairy, eggs. These will putrefy, not ferment. The smell will be unforgettable.
- Oily foods, salad dressing, anything greasy. Oil coats the scraps and blocks the water from doing its job.
- Salt or salted food. Salt inhibits the fermentation.
- Heavily rotted or mouldy material. You want raw scraps, not old ones.
- Woody material: pineapple crown leaves, hard seeds, avocado pits. They will not break down in three months.
- Bread, rice, cereals. These ferment, but not in a way that produces eco enzyme.
Grey area
A few things work but need care.
| Scrap | Verdict | Note |
|---|---|---|
| Banana peel | Yes, but | Softens quickly and clouds the batch. Use no more than a third of the total scraps. |
| Onion and garlic skins | Small amounts | Strong-smelling batches. Fine for cleaning use, less pleasant if you were hoping for citrus. |
| Chilli | Fine | Adds a mild bite. Wear gloves at harvest if you used a lot. |
| Coffee grounds | Small amounts | Colours the liquid dark and shifts the smell. Use up to about a tenth of the total. |
| Tea leaves | Fine | Small quantities are unobtrusive. Very high tannin teas can slow the fermentation. |
Frozen scraps
Perfectly fine, and often more practical than trying to gather enough scraps in a day. Collect them in a bag in the freezer, thaw when you have enough, and start the batch. Freezing does not harm the microbes that are already on the surface of the fruit.
There is no established evidence that any particular fruit produces a stronger or more effective finished liquid. Choose based on what you actually throw away.
Last reviewed: 2026-02-20