previous_change.rb

class Recipe < ActiveRecord::Base

  belongs_to :style, :counter_cache => true

  attribute_method_suffix '_previous_change'

  private

  def attribute_previous_change(attr)
    self.changes[attr]
  end

end

######

@recipe = Recipe.find(1)
@recipe.style_id ## => 1
@recipe.style_id = 2
@recipe.save
@recipe.style_id_previous_change ## =>  [1, 2]