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Quick answer
Walnuts turn bitter mainly because their oil goes rancid: walnut fat is mostly the delicate kind that reacts with air, and heat, light and moisture make that happen faster. In Bangalore the rainy months speed it up, so walnut kernels need an airtight jar and, from August to October, a place in the fridge.
We get more notes about bitter akhrot from Bangalore during the rains than at any other time of year. Usually the walnuts were fine when they arrived. What changed was the air around the jar.
Two kinds of bitter
Not every bitter walnut has gone off, so it helps to tell the two apart.
The skin. The thin papery skin on a walnut kernel has tannins in it, the same sort of compound that makes strong tea dry your mouth. Even a fresh walnut tastes a little bitter because of the skin. A darker skin usually tastes more bitter than a pale one, which is one reason light-coloured kernels are sold as a better grade.
Rancid oil. This is the other kind, and it does not go away. Walnuts are roughly 65 g fat per 100 g, and most of that is polyunsaturated fat. Polyunsaturated fat reacts with oxygen far more readily than the fat in almonds or cashews. When it does, the taste turns sharp and harsh, and it stays at the back of your throat.
The first kind is part of eating a walnut. The second kind means the walnut is past its best.
Why the rains make it worse
Bangalore is rarely hot enough to spoil nuts on heat alone, which is why people are caught out. The trouble is moisture. Through the late monsoon the air holds a lot of water, and every time a jar is opened, some of it gets in.
Damp kernels go soft first. A soft kernel has more of its surface exposed, and the oil starts to go stale sooner. Add a kitchen shelf near a window or a pressure cooker, and a jar that would have lasted months in dry weather tastes off in a few weeks.
Whole, halves or pieces: which keeps longest
The more of a walnut is exposed, the faster it goes. The shell is the best packaging there is.
| Form | How exposed it is | Where to keep it in the wet months |
|---|---|---|
| Walnut Whole (in shell) | Protected by the shell | An airy, dry, cool cupboard; it keeps for months |
| Walnut Kernels Two Pieces (halves) | Open on one face | An airtight jar in the fridge |
| Walnut Kernels Four Pieces (quarters) | Open on several faces | An airtight jar in the fridge; use within a few weeks |
Quarters cost less for the same reason that broken cashews do, as our note on kaju grades explains. They are ideal for cooking and baking. Just buy them in smaller amounts and use them up sooner. All three are on our walnut shelf.
How to store walnuts through the rains
- Move kernels into an airtight glass jar as soon as the pack is open. Fill it close to the top, because less air means slower staling.
- Keep the main jar in the fridge and a small jar outside for the week. For more than a month’s stock, the freezer is better still.
- Let the fridge jar reach room temperature before you open it. Open it cold and water forms on the kernels.
- Use a dry spoon. A wet spoon puts water straight into the jar.
- Keep jars away from the stove, the window and the sunlight. Light speeds up rancidity as much as warmth does.
- Do not mix old kernels with a new pack. Finish the old ones first.
How to tell a stale walnut
- Smell the jar. Fresh walnuts smell faintly nutty. Rancid ones smell of paint, putty or old frying oil.
- Look at the flesh, not the skin. Break a kernel. The inside should be creamy white. A yellow or translucent look means the oil has changed.
- Feel it. A fresh kernel breaks cleanly. A chewy or rubbery one has taken on moisture.
- Taste one. A mild dryness from the skin is normal. A harsh bitterness that stays in your throat is rancid oil.
Some families soak walnuts overnight, which softens the skin and takes away some of its dryness. Toasting fresh walnuts for a few minutes also rounds out the flavour. Neither will rescue a rancid walnut, so if the smell is wrong, throw it out.
Akhrot was running at around at today's shop rate a kilo, depending on the form and grade. Orders reach Bangalore in 3–5 days, and delivery is free on orders over ₹1,000. Below that, a delivery charge is added at checkout. Check today’s dry fruit prices in Bangalore before you order.
Questions people ask
Is it safe to eat bitter walnuts?
A slight bitterness from the skin is normal. Walnuts that smell of paint or old oil have gone rancid and taste bad, and are best thrown away.
Should walnuts be kept in the fridge?
Kernels, yes, in an airtight jar, especially in damp months. Walnuts in the shell keep well in a cool, dry cupboard.
Why do walnuts go bad faster than almonds?
Walnut fat is mostly polyunsaturated, and that kind reacts with air much more readily than the fat in almonds or cashews.
Can I freeze walnuts?
Yes. Freeze them in a well-sealed jar or bag, and take out only what you need, so the rest does not keep warming and cooling.
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Written at our counter, where these questions get asked every week.
