I have seen mostly two suggestions to cool wort. Ice bath and the coil method. My friend and I were thinking about just using ice. Ie pull the ice from the fridge that uses the same water source as used during the boil. Put it in the pale and run the wort into the ice. What are the drawbacks, I'm sure there are some because I can't find anybody recommending this method. For sure it will cool down pretty quickly which is desired.
This is how I do all of my brews. I usually boil about 11/12L for a 20/21L batch, put a filter over the primary bucket, pour the wort in from a bit of a height to help aerate, add ice until I get the right temperature then top up with water. The "right temperature" might be a couple of degrees above / below target, depending on whether the top up water is warm or cold.
I haven't had any contamination problems yet, but it is something to keep in mind. Either make your own ice through freezing boiled water (you'll need a few kgs) or buy it bagged from somewhere you trust that takes cleanliness seriously (distilled, minimal handling, etc). Some places do sell different grades (e.g. triple frozen for making cocktails) so you might be able to find something especially good.
The temperature gets down within a few minutes so it's certainly an effective method. Plus you save potentially hundreds of litres of water per brew. This is the reason I do it: I haven't found a more efficient wort cooling system than this. As baka noted though, it will not work if you are doing a full boil and will become harder as you get closer to a full boil.
I always thought of this as being a HUGE no no. But I guess not...below is from John Palmer.
People often wonder about adding ice directly to the cooling wort. This idea works well if you remember a couple key points.
- Never use commercial ice. It can harbor dormant bacteria that could spoil your beer.
- Always boil the water before freezing it in an airtight container (like Tupperware). It must be airtight because most freezers also harbor dormant bacteria.
- If the ice will not directly contact the wort, (i.e. you are using a frozen plastic soda bottle or other container in the wort) make sure you sanitize the outside of the bottle first before you put it in the wort.
The only problem I can think of might be contamination or (depending on the age of your ice...) picking up off flavors from the ice. Remember that it will also dilute your wort by some (probably calculable) amount. If you're doing a concentrated boil anyway, then it would be easy enough to dump the hot wort onto your extra 2-3 gallons of ice. I imagine that it would get you to pitching temperature more rapidly than other methods, as well.