So I looked up some ice cream making recipes, and have been making ice cream using coconut milk + egg yolks in a double boiler + vanilla extract + stevia + ice cream maker, and I have a few questions since I'm still generally quite new to cooking and think understanding the reasons behind the steps might help me make it better.
1) What exactly is the science behind the custard making. i.e., why exactly am I heating the mixture up? Is it for food safety reasons (raw eggs) or is it for something specific to the ice cream making process? This is especially in regards to the instructions that I'm supposed to cook and whisk until it's custard-like, and I'm not sure I'm getting to that point. So is it because the heat isn't high enough or I'm not whisking enough (and why the need for constant whisking?)
2) I noticed at high enough temp and/or not enough whisking, it seemed like I was seeing a "skin" form on top of the liquid and the sides of the bowl from evaporation (the sides are probably from evaporation and the mixture drying there). Am I doing it wrong/what should I do then?
3) After the ice cream maker was done, I put the mixture in an airtight container and froze it for a day. It seemed kinda gritty to taste, is this because of ice crystals, if so, what can I do to make it even smoother? (I only put the custard in the fridge for about 3 hours after cooking). The vanilla extract also has some alcohol, could that be responsible?
4) Since I'm using canned coconut milk, I'm noticing that the cream tends to separate from the water. Would it be even better if I just scooped the cream out and threw away the water (less water, less crystals that can form?), or will that ruin the ice cream in other ways?