First, a word on this dish
Your first medu vada may come out like a hockey puck, and if it does, the cause is almost certainly in the grinder, not the fryer. These rings look plain, yet the whole appeal sits in the contrast between a shell that crunches and a centre that is nearly weightless, and that contrast is made entirely by how much air you trap in the dal before it hits the oil. Treat it as batter work first and frying second.
In South India it turns up on the tiffin plate next to idli and dosa, and many people happily eat it on its own, torn in half and dragged through sambar or coconut chutney.
The story behind the dish
Medu vada is part of the lentil batter cooking that also gave us idli and dosa. Tamil Nadu, Karnataka and Andhra Pradesh all claim it as a regular on the breakfast table. The name itself describes the interior: medu means soft, and it sets this vada apart from the denser, grittier fritters made from other pulses. How idli and dosa began is still argued over by food historians. Frying ground pulses is a different matter, being among the oldest and most widespread snack methods anywhere on the subcontinent, and the urad dal vada of the South is simply a well-established regional version of that old idea. Nothing about its story is contested.
The method, in order
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Prep
Grind stingily with the water
Drain the dal well, then start the grinder and add cold water by the tablespoon, only when the blades start to stall. Keep going until the batter is thick, white and visibly puffed up. This stage decides everything. Pouring in water to make grinding easier is the most common way to ruin the batch, because a wet batter cannot hold air.
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Prep
Float a spoonful to check
Spoon a small blob into a bowl of cold water. If it bobs on the surface, there is enough air in it. If it drops, beat the batter with your hand in one direction for a few minutes, then test again.
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Prep
Fold in the seasonings
Add the chilli, ginger, pepper, cumin, curry leaves, onion if you want it, hing and salt, and turn them in with a few slow folds. Stirring hard would knock out the air you have just built.
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Assemble
Make rings on a wet palm
Dampen your hand, or a piece of plastic sheet, so nothing sticks. Take a lump of batter, flatten it to a disc about 2 1/2 inches wide, and push a wet finger through the centre. The hole is traditional, but it has a practical purpose as well: a solid blob would be brown outside long before the middle cooked.
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Cook
Slide into hot oil and brown
The oil should sit at 170 to 180°C, roughly 340 to 350°F. Tip each ring in from your palm or the plastic with a quick, low motion, so the oil does not splash you. Cook 3 or 4 together for 4 to 5 minutes, flipping them now and then, until they are a deep gold and crisp when you press the edge.
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Serve
Drain and bring to the table hot
Set them on a wire rack for a minute, then serve with coconut chutney and sambar. If you like, drop one into a bowl of warm sambar and let it soak briefly. That softer, wetter version is called sambar vada.
Ingredient stand-ins
You can drop the onion. Some cooks always do, particularly for temple food, where onion and garlic are left out, and the vada is no worse for it. Use less pepper if you want a calmer flavour, since pepper gives a sharp bite that is a separate thing from chilli heat.
Making it milder or fiercer
Chilli warms you gradually while pepper hits straight away, so treat them as two separate controls and not one. For a gentle batch, cut both back. If you want more heat, add green chilli first, because extra pepper turns harsh sooner than you expect.
The slip most cooks make
A heavy, doughy vada points back to too much water in the grinder. A batter that slumps and will not keep its ring shape has the same cause, or the dal went into the grinder still dripping from its soak. When the shape holds on a wet palm, the consistency is right. If the vada brown fast but feel raw in the centre when you break one open, the oil was hotter than it should have been.
Storing what is left
Fridge or counter: Fry the batter the day you make it. The air leaves it slowly as it stands, and each hour it waits gives you a denser vada. A few hours in a covered bowl in the fridge is the most you should ask of it. Fried vada stay good in the fridge for up to two days, and they come back to life best in a warm bath of sambar.
Bringing it back to life: An oven or air fryer at 180°C (350°F) for 6 to 8 minutes restores a little crunch. If you would sooner not chase crispness, soak them briefly in hot sambar instead.
Handle with care
Keep the oil temperature steady, stay close to the pot, and replace the oil once it turns very dark or begins to smoke below the point where fresh oil would. This batter is not fermented, so there is no fermentation to worry about, but if you plan to hold it for longer than an hour or two before frying, keep it cold.