diff --git a/CHANGELOG.md b/CHANGELOG.md
index c55b7c1..e63b85a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,13 @@
+### 2.2.0 (2018-07-24)
+
+Features:
+
+    - Let `Eeny::Meeny::Middleware` remove deprecated experiment cookies (for undefined and inactive experiements)
+
+Changes:
+
+    - Renamed `EenyMeeny::Cookie::COOKIE_PREFIX` to `EenyMeeny::Cookie::EXPERIMENT_PREFIX`
+
 ### 2.1.4 (2017-10-04)
 
 Changes:
diff --git a/eeny-meeny.gemspec b/eeny-meeny.gemspec
index 7ed7587..302f19e 100644
--- a/eeny-meeny.gemspec
+++ b/eeny-meeny.gemspec
@@ -3,7 +3,7 @@ require File.expand_path('../lib/eeny-meeny/version', __FILE__)
 Gem::Specification.new do |s|
   s.name        = 'eeny-meeny'
   s.version     = EenyMeeny::VERSION.dup
-  s.date        = '2017-10-04'
+  s.date        = '2018-07-24'
   s.summary     = "A simple split and smoke testing tool for Rails"
   s.authors     = ["Christian Orthmann"]
   s.email       = 'christian.orthmann@gmail.com'
diff --git a/lib/eeny-meeny/middleware.rb b/lib/eeny-meeny/middleware.rb
index 14de816..9de241a 100644
--- a/lib/eeny-meeny/middleware.rb
+++ b/lib/eeny-meeny/middleware.rb
@@ -24,34 +24,15 @@ def call(env)
       query_parameters = query_hash(env)
       now              = Time.zone.now
       new_cookies      = {}
+      delete_cookies   = find_deprecated_cookies(cookies, now)
       # Prepare for experiments.
       @experiments.each do |experiment|
         # Skip inactive experiments
         next unless experiment.active?(now)
-        # Trigger experiment through query parameters
-        cookie_name = EenyMeeny::Cookie.cookie_name(experiment)
-        has_experiment_trigger = EenyMeeny.config.query_parameters[:experiment] && query_parameters.key?(cookie_name)
-        # skip experiments that already have a cookie
-        next unless has_experiment_trigger || !cookies.key?(cookie_name)
-        cookie = if has_experiment_trigger
-                   # Trigger experiment variation through query parameter.
-                   EenyMeeny::Cookie.create_for_experiment_variation(experiment, query_parameters[cookie_name].to_sym, @cookie_config)
-                 else
-                   EenyMeeny::Cookie.create_for_experiment(experiment, @cookie_config)
-                 end
-        # Set HTTP_COOKIE header to enable experiment on first pageview
-        env = add_or_replace_http_cookie(env, cookie)
-        new_cookies[cookie.name] = cookie
-      end
-      # Prepare smoke tests (if enabled through query parameters)
-      if EenyMeeny.config.query_parameters[:smoke_test]
-        if query_parameters.key?('smoke_test_id') && (query_parameters['smoke_test_id'] =~ /\A[A-Za-z_]+\z/)
-          # Set HTTP_COOKIE header to enable smoke test on first pageview
-          cookie = EenyMeeny::Cookie.create_for_smoke_test(query_parameters['smoke_test_id'], @cookie_config)
-          env = add_or_replace_http_cookie(env, cookie)
-          new_cookies[cookie.name] = cookie
-        end
+        env, new_cookies = prepare_experiment(env, cookies, new_cookies, query_parameters, experiment)
       end
+      # Prepare smoke tests
+      env, new_cookies = prepare_smoke_test(env, new_cookies, query_parameters)
       # Delegate to app
       status, headers, body = @app.call(env)
       response = Rack::Response.new(body, status, headers)
@@ -59,11 +40,57 @@ def call(env)
       new_cookies.each do |key, value|
         response.set_cookie(key,value.to_h)
       end
+      delete_cookies.each do |key, value|
+        response.delete_cookie(key, value: value, path: @cookie_config[:path], same_site: @cookie_config[:same_site])
+      end
       response.finish
     end
 
     private
 
+    def find_deprecated_cookies(cookies, now)
+      deprecated_cookies = {}
+      cookies.each do |cookie_name, value|
+        # Skip any cookie that does not have the 'eeny_meeny_' prefix
+        next unless cookie_name.to_s.start_with?(EenyMeeny::Cookie::EXPERIMENT_PREFIX)
+        # Mark cookies that does not match any existing active experiment as 'deprecated'.
+        experiment = EenyMeeny::Experiment.find_by_cookie_name(cookie_name)
+        next if experiment && experiment.active?(now)
+        deprecated_cookies[cookie_name] = value
+      end
+      deprecated_cookies
+    end
+
+    def prepare_experiment(env, cookies, new_cookies, query_parameters, experiment)
+      # Trigger experiment through query parameters
+      cookie_name = EenyMeeny::Cookie.cookie_name(experiment)
+      has_experiment_trigger = EenyMeeny.config.query_parameters[:experiment] && query_parameters.key?(cookie_name)
+      # Skip experiments that already have a cookie
+      return env, new_cookies unless has_experiment_trigger || !cookies.key?(cookie_name)
+      cookie = if has_experiment_trigger
+                 # Trigger experiment variation through query parameter.
+                 EenyMeeny::Cookie.create_for_experiment_variation(experiment, query_parameters[cookie_name].to_sym, @cookie_config)
+               else
+                 EenyMeeny::Cookie.create_for_experiment(experiment, @cookie_config)
+               end
+      # Set HTTP_COOKIE header to enable experiment on first pageview
+      env = add_or_replace_http_cookie(env, cookie)
+      new_cookies[cookie.name] = cookie
+      return env, new_cookies
+    end
+
+    def prepare_smoke_test(env, new_cookies, query_parameters)
+      # Skip if the EenyMeeny 'smoke test' query parameters configuration is disabled.
+      return env, new_cookies unless EenyMeeny.config.query_parameters[:smoke_test]
+      # Skip if no valid 'smoke_test_id' query parameter present
+      return env, new_cookies unless query_parameters.key?('smoke_test_id') && (query_parameters['smoke_test_id'] =~ /\A[A-Za-z_]+\z/)
+      # Set HTTP_COOKIE header to enable smoke test on first pageview
+      cookie = EenyMeeny::Cookie.create_for_smoke_test(query_parameters['smoke_test_id'], @cookie_config)
+      env = add_or_replace_http_cookie(env, cookie)
+      new_cookies[cookie.name] = cookie
+      return env, new_cookies
+    end
+
     def query_hash(env)
       # Query Params are only relevant if EenyMeeny.config have them enabled.
       return {} unless EenyMeeny.config.query_parameters[:experiment] || EenyMeeny.config.query_parameters[:smoke_test]
diff --git a/lib/eeny-meeny/models/cookie.rb b/lib/eeny-meeny/models/cookie.rb
index 2e10711..aafb3b7 100644
--- a/lib/eeny-meeny/models/cookie.rb
+++ b/lib/eeny-meeny/models/cookie.rb
@@ -2,7 +2,7 @@
 
 module EenyMeeny
   class Cookie
-    COOKIE_PREFIX = 'eeny_meeny_'.freeze
+    EXPERIMENT_PREFIX = 'eeny_meeny_'.freeze
     SMOKE_TEST_PREFIX = 'smoke_test_'.freeze
 
     attr_accessor :value
@@ -52,7 +52,7 @@ def self.smoke_test_name(smoke_test_id, version: 1)
 
     def self.cookie_name(experiment)
       return if experiment.nil?
-      COOKIE_PREFIX+experiment.id.to_s+'_v'+experiment.version.to_s
+      EXPERIMENT_PREFIX+experiment.id.to_s+'_v'+experiment.version.to_s
     end
 
     def self.read(cookie_string)
diff --git a/lib/eeny-meeny/models/experiment.rb b/lib/eeny-meeny/models/experiment.rb
index 3681444..a29f172 100644
--- a/lib/eeny-meeny/models/experiment.rb
+++ b/lib/eeny-meeny/models/experiment.rb
@@ -4,6 +4,9 @@
 
 module EenyMeeny
   class Experiment
+
+    COOKIE_EXPERIMENT_ID_REGEX = /\Aeeny_meeny_(.+)_v\d+\z/.freeze
+
     attr_reader :id, :name, :version, :variations, :total_weight, :end_at, :start_at
 
     def self.find_all
@@ -17,6 +20,12 @@ def self.find_by_id(experiment_id)
       new(experiment_id, **experiment) if experiment
     end
 
+    def self.find_by_cookie_name(cookie_name)
+      if cookie_name =~ COOKIE_EXPERIMENT_ID_REGEX
+        find_by_id($1)
+      end
+    end
+
     def initialize(id, name: '', version: 1, variations: {}, start_at: nil, end_at: nil)
       @id = id
       @name = name
diff --git a/lib/eeny-meeny/version.rb b/lib/eeny-meeny/version.rb
index f6d5355..81e96c9 100644
--- a/lib/eeny-meeny/version.rb
+++ b/lib/eeny-meeny/version.rb
@@ -1,3 +1,3 @@
 module EenyMeeny
-  VERSION = '2.1.4'
+  VERSION = '2.2.0'
 end
diff --git a/spec/eeny-meeny/middleware_spec.rb b/spec/eeny-meeny/middleware_spec.rb
index ae9fe1b..ef863a6 100644
--- a/spec/eeny-meeny/middleware_spec.rb
+++ b/spec/eeny-meeny/middleware_spec.rb
@@ -70,6 +70,22 @@ def initialize_app(secure: true, secret: 'test', path: '/', same_site: :strict)
       end
     end
 
+    context 'and the request contains a cookie from an undefined experiment' do
+      let(:request) { Rack::MockRequest.new(subject) }
+
+      before(:example) do
+        @original_request_cookies = 'test=abc;eeny_meeny_undefined_experiment_v1=thevaluedoesntmatter;'
+        @response = request.get('/test',
+                                'CONTENT_TYPE' => 'text/plain',
+                                'HTTP_COOKIE' => @original_request_cookies)
+      end
+
+
+      it "instructs the browser to remove through the 'Set-Cookie' header on the response" do
+        expect(@response['Set-Cookie']).to include('eeny_meeny_undefined_experiment_v1=thevaluedoesntmatter; path=/; max-age=0; expires=Thu, 01 Jan 1970 00:00:00 -0000; SameSite=Strict')
+      end
+    end
+
     context 'and given an experiment query parameter' do
       let(:request) { Rack::MockRequest.new(initialize_app(secure: false)) }
 
diff --git a/spec/eeny-meeny/models/experiment_spec.rb b/spec/eeny-meeny/models/experiment_spec.rb
index 5c2f92f..01cd73d 100644
--- a/spec/eeny-meeny/models/experiment_spec.rb
+++ b/spec/eeny-meeny/models/experiment_spec.rb
@@ -194,4 +194,17 @@ def experiment_with_time(time = {})
     end
   end
 
+  describe '.find_by_cookie_name', experiments: true do
+    context 'when the given cookie name matches a configured experiment' do
+      it 'returns the experiment' do
+        expect(described_class.find_by_cookie_name(:eeny_meeny_my_page_v1)).to be_a EenyMeeny::Experiment
+      end
+    end
+
+    context 'when the given cookie name does not match a configured experiment' do
+      it 'returns nil' do
+        expect(described_class.find_by_cookie_name(:eeny_meeny_undefined_experiment_v2)).to be_nil
+      end
+    end
+  end
 end