I've seen that sugar is used to balance out other flavors in a dish. I was just wondering if I could add a little sugar to a spicy curry(chicken curry, for example). Would that take away the authentic flavor? If no, then how much can be safely added before it becomes too sweet?
There is nothing inauthentic about using sugar in an Indian dish, even a savory one. For example, Gujarati cooks often add raw sugar (jaggery) to daal and curries. Quoth Wikipedia:
"It is common to add a little sugar or jaggery to some of the sabzi/shaak and daal. The sweet flavour of these dishes is believed to neutralize the slightly salty taste of the water."
And here's an example Gujarati potato curry recipe, which includes a tablespoon of sugar.
As for how much to add, that's a matter of your taste and the level of acidity and/or saltiness in the dish. My Gujarati friends in Boston like stuff rather sweeter than I would personally prefer, so be cautious.
I have a restaurant in Delhi.
Whether you add sugar to a curry really depends on the region you're cooking is from.
A Kashmiri dish will usually never have sugar in it, but may have raisins or dates added if sweetness is required.
In contrast & (as previously mentioned) most savory Bengali dishes will have a bit of sugar added (my Kashmiri husband hates this).
It is also interesting to note that the type of onion most commonly used in India is a small pink/red onion that has quite a bit of sugar. That is where the caramelized 'sweetness' in many Indian dishes comes from.
And yes, it is quite an 'art' to get those tonnes of onions perfectly caramelized!
I have a recipe book for cooking curries 'just like an Indian restaurant'. The most glaringly obvious point is that just about every curry (except cream-based ones like kormas) start off with tons of onions, sweated for hours.
This releases a lot of natural sugars from the onions, so most restaurant curry sauces do have an underlying sweetness. Obviously most home cooks don't have hours to spend sweating onions, so naturally their curries don't taste quite the same. Adding sugar recreates the sweetness somewhat. Their are other factors (like adding half a tin of ghee to every curry), but it does help and there's nothing wrong with it.
I find that sugar gets added to the curries from Malaysia, Singapore, Thailand etc sometimes.
They are usually sour and sweet, eg use tamarind and tart ingredients like lemongrass, or very salty smelly like blachan or fish sauce. these need leavening with sugar so follow the recipe for good results.
Adding sugar on the off chance I would be less certain of. A garnish of half a sliced onion, fried until brown, and added last, will typically work well, esp with lentil dhals as the caramel in the onions comes through
Given that Masala based curries always get some sweetness from tomatoes (which could be anything from sour to rather sweet), and it is generally a good idea to balance tomato based sauces of all kinds with sweet (sugar, jaggery)/sour (yoghurt, vinegar) ingredients at the end, how could one find fault with this?