title_body: Brikka either too bubbly crema or doesn't work
upvoted_answer: The Brikka has a safety valve  integrated in the base which should prevent blowing up. However, the coffee will likely be burnt if the steam comes out of the side for a long time. You can try using a lond spoon/knife to lift the weight manually to not waste the coffee.
  Generally I would advise against tamping the coffee at all. The amount of pressure it needs to lift the weight and the point where the safety valve opens isn't too far apart. If you tamp, the water needs to exert pressure against the coffee and the weight which is often too much or takes too long.
  The key is to find the correct grind size. Start with too coarse, fill the basket, remove excess from top and don't tamp. The coffee should extract quickly with a sigle "swoosh" but taste and crema will be on the light side.
  Now start reducing the grind size until you hear a bit of a strain in the "swoosh" and it will take a bit longer. This is the point you are aiming for. Since the Brikka does preinfusion, the swelling grounds will provide enough resistance to get the oils out and thus the crema. If the safety valve opens, it was too fine.
  The most important measure of coffee is taste, so I'd suggest try to get the taste right before worrying about how the crema looks which is very dependent on the beans, their age, the roast. (dark roasts with lots of robusta if you want crema) Keep in mind that not all roasts are equally suited for the brikka and that due to the lower pressure you won't get the same kind of crema a portafilter machine will make.