Whether the snack is a samosa, a kachori, a pakora or a vada, the oil decides how it turns out, and generations of Indian home cooks have judged that heat by eye and ear rather than by instrument. The same habit runs the sweet-and-snack shops that keep their kadhais going from early morning to late evening, so working this way is hardly a shortcut; it is the method as it was always taught. A pot that is a little too cool or a little too hot ruins more batches than a mediocre dough or a misjudged spice mix, which makes learning to read the oil one of the most rewarding habits a home cook can build.
Reading the heat without a thermometer
Cooks usually begin with a small drop of batter or a pea-sized piece of dough, released into the oil and watched closely. When it falls to the bottom and lingers there before creeping upward, the oil has not yet warmed enough. When it dips briefly and then bobs up within a second or two, surrounded by a lively ring of fine bubbles, you are in the range suited to most frying, around 170 to 180°C (340 to 355°F). When it leaps to the top and starts to colour almost immediately, the oil has gone too far. A dry wooden spoon handle works as a second opinion, since a steady stream of small bubbles along the wood signals readiness, big rolling bubbles signal excess heat, and a bare, silent handle signals that you should wait. Each trick measures the same thing, namely how fast the oil converts surface moisture into steam, and that response tracks temperature closely enough to cook by even when no degree reading is available.
Why the oil cools when food is lowered in
Anything you add has to be heated up from its own temperature, and the energy comes from the oil around it, so the pot cools at the very moment you most need it hot, by as much as 15 to 20°C when the pot is small. A larger load or colder ingredients make that dip deeper, which explains why the first minute after each addition is the trickiest. The remedy is to nudge the burner higher as the food enters and bring it back down once the bubbling turns steady, instead of setting the flame once and walking away. Cold ingredients straight from the refrigerator deepen the problem and invite greasy, underdone results, so chilled dough or battered vegetables are better given a few minutes on the counter before they meet the oil.
Frying a little at a time
Packing too many pieces into the pot is how most people end up with oil that sags and never recovers, because the cold food absorbs heat faster than the flame can supply it, leaving pale, oily, slow-cooked results where crisp ones were intended. A sensible limit is a third to a half of the oil surface covered at any moment, so every piece has room to float and turn. After each round, wait 30 to 60 seconds for the temperature to rebuild and run the batter test once more before you commit the next lot. Several small rounds cost more time than one large one, but they repay it with an evenness that a crowded pot cannot match.
Two-stage frying
Thick or dense pieces, including whole samosas, chunky kachori and vada made from soaked, ground lentils, are best cooked in two passes at different heats. The opening pass uses gentler oil, about 150 to 160°C (300 to 320°F), which gives the centre time to cook before the surface hardens and seals raw dough or filling inside. After that, the pieces come out to rest briefly while the oil is raised to about 180°C (355°F), and a quick return to the pot crisps and colours the outside. The method addresses a very common disappointment, the snack that is handsomely golden on the outside but pasty in the middle, which happens when one fast, hot fry browns the exterior long before the heat has reached the core.
What a smoking pot is telling you
Each oil has a smoke point, the temperature beyond which it no longer merely heats but starts to decompose and release visible smoke. Past that line the oil turns bitter and acrid and fries less cleanly. Oil that has been used before reaches that line sooner than fresh oil, since earlier frying has already broken down part of it and left tiny food particles behind, and the threshold drops again with each reheating. If a pot smokes before any food has gone in, do not fry in it for that batch, and never leave oil heating on its own beyond the first shimmer and drift across its surface, because oil that is already smoking has gone past where it ought to be.
Reusing oil, and when to retire it
A few reuses are reasonable provided you look after the oil: strain it through a fine sieve or cheesecloth while it is still warm so food particles are removed, let it cool fully, then store it in a sealed container somewhere dark and cool. Every round of frying wears it down further, so the number of reuses has a limit, and the oil should go once it smokes noticeably earlier than before, smells rancid or sharp rather than neutral, turns dark and thick, or froths in an unusual way when food enters. Oil from lightly battered pakoras can often be used two or three times if strained and stored well, but oil that has fried pungent or heavily spiced foods tends to be worth discarding sooner, since it hands those flavours to whatever you fry next.
Letting oil cool and getting rid of it safely
Pouring hot oil into a sink is never acceptable, because it can harm the pipes once it cools and sets, and it is a serious burn and fire risk while it is hot. Leave used oil in its pot until it has cooled all the way before touching it. For disposal, pour it into a sealable container that does not go for recycling, such as an old jar or carton, and put it out with the ordinary household rubbish instead of tipping it anywhere it might spill or ignite. While frying, keep the pot on a rear burner out of the way of elbows, point the handles inward, and have a lid within reach to smother a stovetop oil fire, remembering that water must never be thrown on burning oil because it sends the oil spattering violently rather than putting the fire out.