Few ingredients do as much work in the snack kitchens of western and northern India as besan, the flour milled from chickpeas, and few are as easy to misjudge, because the same flour must behave in quite different ways from one dish to the next. For a pakora it needs to be thick and clingy, for steamed dhokla light and slightly aerated, and for khandvi thin enough to spread into a paper-thin layer while still setting firm once cooked. A soggy pakora, a dense dhokla and a khandvi that will not roll almost always come from the wrong thickness or the wrong rest for that particular dish, and rarely from the flour itself.
Keeping lumps out
Besan clumps readily when liquid is added too fast, because the fine particles on the surface of a clump absorb water and seal dry flour inside. The dependable cure is to whisk the flour with its spices and salt while still dry, then add water a few tablespoons at a time, whisking constantly, instead of pouring it in all at once. Sifting the flour first removes clumps that already exist, which helps most with flour that has sat in a container and compacted. If lumps still form, pushing the batter through a sieve with the back of a spoon works better than whisking, since whisking alone often just breaks big lumps into smaller ones without dissolving them.
Pakora batter, thick enough to cling
Think of a thick pancake batter and you are close to what bhajiyas and pakoras need. Dip a vegetable slice, and a visible, even layer should stay on it instead of draining away; lifting the whisk, you want the batter to fold back over itself slowly. Go thinner and the coating turns into a weak, see-through shell that never crisps. Go thicker and the centre stays doughy while the surface darkens. Replacing roughly a fifth of the besan with rice flour or cornflour is a habit of many stall cooks, because those starches fry up lighter and stay crisp longer after the pakoras cool. Ten to fifteen minutes of standing before frying lets the flour finish absorbing water, and the coating then grips damp or oily vegetables better.
Dhokla and khandvi, thinner and smoother
Dhokla is steamed in a tin, so its batter must be pourable and medium in body, rather like crepe batter, and it needs something to lift it, either the quick fruit-salt-and-eno route or a slower fermentation. Khandvi goes much further toward the liquid end, almost to the feel of milk, because the cook pours it out and spreads it into a very thin sheet that must firm up as it cooks, with no rising involved. To check a khandvi mixture, cook a spoonful on a plate for about a minute and try to roll it: if it cracks or stays tacky, cook the next batch a little longer or make the batter slightly thicker, as one that is too runny will never set firmly enough to lift off the plate in one piece.
Three pictures of thickness
It helps to hold three images in mind when judging besan batter by eye. The first is the ribbon, in which batter pours from a lifted spoon in a slow fold that rests on the surface for a moment before disappearing, which is the right picture for thick dhokla batters and for some coatings around stuffed pakoras. The second is the coating, in which batter leaves an even, opaque film on the back of a spoon and does not run straight off, the picture for ordinary pakoras. The third is the stream, in which batter pours thin and continuous, the picture for khandvi and for the thinner dosa-like preparations of besan. A quick comparison against these before cooking begins costs seconds and saves the batter that would otherwise be wasted on a bad first piece.
Correcting a batter that is too thick or too thin
Overly stiff batter is simple to loosen, though patience helps: sprinkle in a spoonful of water, whisk, look, and repeat, because besan thickens in an uneven way and a heavy hand swings it too far the other direction. Overly runny batter needs a gentler fix, since scattering dry flour on top brings back the clumps you worked to avoid. Stir a small portion of besan with a splash of water in a separate cup until it is silky, then pour that slurry through the main bowl, where it disperses evenly. If the bowl has gone thicker while resting, nothing is wrong, because the flour is still soaking up water, and a last-minute splash is nearly always needed whatever the batter looked like at first.
Salt, acid and the pace of rising
Where a besan batter has to lift through fermentation or a fast chemical reaction, as opposed to steam alone, the order in which salt and acid go in changes the speed. Salt tends to slow the souring a little, partly because it draws water out and partly because it firms up the proteins in the flour, so cooks planning a batter that will ferment for hours often add it later. Acid does the reverse: a spoonful of yogurt, or lemon juice in a quick dhokla mix, makes baking soda or fruit salt react faster and bubble harder, a useful trick when time is short and you still want a lighter crumb than plain batter gives. After a few hours at room temperature the surface should look slightly puffed and dotted with small bubbles. If nothing has changed in a warm kitchen, suspect an inactive leavener or a cool room, and in that case a gentle warming is a better answer than simply waiting.
Resting and holding the batter
Most besan batters improve with a short rest, about 10 minutes for a plain pakora batter and 20 to 30 minutes for dhokla, because the flour needs that time to take up water completely, and the finished dish comes out smoother. Since besan keeps drinking liquid and settling while it stands, a rested batter, especially one kept in a warm kitchen, usually wants a fast whisk and a little extra water right before cooking. Pakora batter left over does not last past a few hours at room temperature; if it must wait, refrigerate it, then let it warm up and whisk it again before frying.