Banana chips is one of the most popular snacks in Kerala. It holds a very important place in a traditional Kerala sadya. In fact there is no onam without banana chips!! When we were kids we used to call it ‘zero upperi’ and jack fruit chips as ‘one upperi’ 
Ingredients
Raw Banana - 4 kg
Salt - 1 tbsp or as required, dissolved in 1/2 cup water, for sprinkling
Turmeric powder - 1/2 - 3/4 tsp
Coconut Oil - To deep fry
Method
1. Peel off the plantains and put them in turmeric water(mix 1/2 tsp turmeric powder in enough water), for about 15 mts. Drain the excess water and leave to dry or pat dry with paper towels. Heat oil in an uruli or a deep, wide mouthed pan at a medium high flame. Be sure not to fill oil more than half - 3/4 th of the pan you are using. The oil should be really hot.( You can test the oil by adding a slice of banana, it would immediately come to the surface bubbling). Slice the plantains to thin rounds. While slicing, remember to apply some oil in your palms to prevent black stains.
2. When the oil is hot enough, bring down the flame to medium and add the sliced bananas carefully to deep fry. Stir immediately for a few seconds, then bring back the flame to medium high. Do not overcrowd, fry them in batches. (You could also slice them directly into the hot oil using a slicer.) Let the sliced bananas cook for 15 - 20 mts (this time depends on the type of pan you are using. We used an uruli and fried them in 2 batches). You can stir it occasionally using a slotted spoon flipping on both sides but be really careful otherwise the banana slices might break.
3. Meanwhile keep aside 1 tbsp salt and a pinch of turmeric powder in 1/2 cup water(adding turmeric powder is optional, we didn’t add it). When the chips are almost done(you can hear a crisp sound and the oil will stop foaming, you can also taste check whether its done or not), reduce the heat and sprinkle a little salt-turmeric water(you do not need to add more than 1-2 tsp) into the oil carefully. Move away from the pan after sprinkling since the oil might come up and splash making lots of bubbling noise. You can cover it with a lid immediately after sprinkling salt-turmeric water, remove it when the oil stops splashing. When the bubbles stop coming, stir well and drain on to a colander(do not forget to keep a container or plate below the colander to catch any oil drippings). (If you do not wish to add salt water into the oil, you can sprinkle it immediately when they are drained onto the colander. Just make sure to mix well after sprinkling it.)
4. Now transfer the chips into a paper towel or newspaper spread in a muram(wide bamboo tray) or any plate. Repeat for the next batches. Remember to sprinkle less salt water for the next batches as the oil already contains some salt that you added before. Cool and store them in an airtight container.
