gistfile1.rb

class Kitchen < ActiveRecord::Base
  has_many :cups
end

class Cup < ActiveRecord::Base
  has_many :liquids
  belongs_to :kitchen
end

class Liquid < ActiveRecord::Base
  belongs_to :cup
  has_one :kitchen. :through => :cup
end

scope is a good way to go but this should work as well in rails 3. have not tested but should work but maybe not the most efficient thing ever. just cool you can do it.

first load kitchen with your id:

kitchen.cups.liquids.where(:hot => true)