What makes crema?
Crema is a foam comprising coffee oils, carbon dioxide created during coffee roasting and air trapped in coffee grounds. There are several exhaustive Coffeegeek articles in the subject. (I also think electric-pump-based coffee/espresso machines increase crema by aerating brewing water.)
Why there is little crema in coffee from Aeropress?
Oils and bubbles, being lighter than water, travel up when brewing. When Aeropress is used as described in the manual, crema is filtered last and gets absorbed in the grounds and paper filter.
What’s more, absence of oils changes taste of coffee.
Inverted Aeropress Method
The solution is to brew in Aeropress inverted and extract crema first, then upend it into the cup and continue extraction in regular fashion.
Using stainless steel filter is strongly recommended to minimize absorption by paper filter
I also recommend Aeropress Crema Attachment I 3d-printed on Shapeways, but you can use any suitable border you can fashion.
- Use freshly roasted coffee beans
- Brew as soon as possible after grinding
- Do not exceed brewing water temperature (204F/95.5C)
- Use more coffee!