diff --git a/app/services/preservation_ingest_service.rb b/app/services/preservation_ingest_service.rb
index 2fb41181e..185be4205 100644
--- a/app/services/preservation_ingest_service.rb
+++ b/app/services/preservation_ingest_service.rb
@@ -11,50 +11,62 @@ class PreservationIngestService
   # @return [void] Create the Moab/bag manifests for new version, export data to BagIt bag, kick off the SDR preservation workflow
   # @raise [Preservation::Client::Error] if bad response from preservation catalog.
   def self.transfer(cocina_object)
-    druid = cocina_object.externalIdentifier
-    workspace = DruidTools::Druid.new(druid, Settings.sdr.local_workspace_root)
-    signature_catalog = signature_catalog_from_preservation(druid)
-    new_version_id = signature_catalog.version_id + 1
+    new(cocina_object).transfer
+  end
+
+  def initialize(cocina_object)
+    @cocina_object = cocina_object
+  end
+
+  # @param [Cocina::Models::DRO, Cocina::Models::Collection] cocina_object The representation of the digital object
+  # @return [void] Create the Moab/bag manifests for new version, export data to BagIt bag, kick off the SDR preservation workflow
+  # @raise [Preservation::Client::Error] if bad response from preservation catalog.
+  def transfer
+    # Writes versionMetadata.xml, contentMetadata.xml, and cocina.json
     metadata_dir = PreservationMetadataExtractor.extract(workspace:, cocina_object:)
+
+    # Makes sure that the versionMetadata.xml version matches the expected version from preservation.
     verify_version_metadata(metadata_dir, new_version_id)
-    version_inventory = Preserve::FileInventoryBuilder.build(metadata_dir:,
-                                                             druid:,
-                                                             version_id: new_version_id)
+    # Creates a Moab::FileInventory from the contentMetadata.xml
+    version_inventory = Preserve::FileInventoryBuilder.build(metadata_dir:, druid:, version_id: new_version_id)
+
+    # Creates a Moab::FileInventory containing only the files that are changed in this version.
     version_additions = signature_catalog.version_additions(version_inventory)
+
+    # Find the changed files in the workspace
     content_additions = version_additions.group('content')
-    if content_additions.nil? || content_additions.files.empty?
-      content_dir = nil
-    else
+    content_dir = nil
+    if content_additions.present? && content_additions.files.any?
       new_file_list = content_additions.path_list
       content_dir = workspace.find_filelist_parent('content', new_file_list)
     end
+
     content_group = version_inventory.group('content')
+
+    # Regenerate the fixitites for content (md5, sha1, sha256) if they are missing.
     signature_catalog.normalize_group_signatures(content_group, content_dir) unless content_group.nil? || content_group.files.empty?
-    # export the bag (in tar format)
-    bag_dir = Pathname(Settings.sdr.local_export_home).join(druid.sub('druid:', ''))
-    bagger = Moab::Bagger.new(version_inventory, signature_catalog, bag_dir)
-    bagger.reset_bag
-    bagger.create_bag_inventory(:depositor)
-    bagger.deposit_group('content', content_dir)
-    bagger.deposit_group('metadata', metadata_dir)
-    bagger.create_tagfiles
-    Preserve::BagVerifier.verify(directory: bag_dir)
+
+    export(version_inventory, content_dir, metadata_dir)
   end
-  # NOTE: the following methods should probably all be private
 
-  # @param [String] druid The object identifier
+  private
+
+  attr_reader :cocina_object
+
   # @return [Moab::SignatureCatalog] the manifest of all files previously ingested,
   #   or if there is none, a SignatureCatalog object for version 0.
   # @raise [Preservation::Client::Error] if bad response from preservation catalog.
-  def self.signature_catalog_from_preservation(druid)
-    Preservation::Client.objects.signature_catalog(druid)
-  rescue Preservation::Client::NotFoundError
-    Moab::SignatureCatalog.new(digital_object_id: druid, version_id: 0)
+  def signature_catalog
+    @signature_catalog ||= begin
+      Preservation::Client.objects.signature_catalog(druid)
+    rescue Preservation::Client::NotFoundError
+      Moab::SignatureCatalog.new(digital_object_id: druid, version_id: 0)
+    end
   end
 
   # @param [Pathname] metadata_dir the location of the metadata directory in the workspace
   # @param [Integer] expected the version identifer expected to be used in the versionMetadata
-  def self.verify_version_metadata(metadata_dir, expected)
+  def verify_version_metadata(metadata_dir, expected)
     vmfile = metadata_dir.join('versionMetadata.xml')
     verify_version_id(vmfile, expected, vmfile_version_id(vmfile))
     true
@@ -63,7 +75,7 @@ def self.verify_version_metadata(metadata_dir, expected)
   # @param [Pathname] pathname The location of the file containing a version number
   # @param [Integer] expected The version number that should be in the file
   # @param [Integer] found The version number that is actually in the file
-  def self.verify_version_id(pathname, expected, found)
+  def verify_version_id(pathname, expected, found)
     raise "Version mismatch in #{pathname}, expected #{expected}, found #{found}" unless expected == found
 
     true
@@ -71,7 +83,7 @@ def self.verify_version_id(pathname, expected, found)
 
   # @param [Pathname] pathname the location of the versionMetadata file
   # @return [Integer] the versionId found in the last version element, or nil if missing
-  def self.vmfile_version_id(pathname)
+  def vmfile_version_id(pathname)
     raise "#{pathname.basename} not found at #{pathname}" unless pathname.exist?
 
     doc = Nokogiri::XML(File.read(pathname.to_s))
@@ -79,4 +91,29 @@ def self.vmfile_version_id(pathname)
     version_id = nodeset.last['versionId']
     version_id&.to_i
   end
+
+  # Export the bag (using symlinks for content files)
+  def export(version_inventory, content_dir, metadata_dir)
+    bag_dir = Pathname(Settings.sdr.local_export_home).join(druid.sub('druid:', ''))
+    bagger = Moab::Bagger.new(version_inventory, signature_catalog, bag_dir)
+    bagger.reset_bag
+    bagger.create_bag_inventory(:depositor)
+    bagger.deposit_group('content', content_dir)
+    bagger.deposit_group('metadata', metadata_dir)
+    bagger.create_tagfiles
+    # Checks for required files. (Does not check fixities.)
+    Preserve::BagVerifier.verify(directory: bag_dir)
+  end
+
+  def druid
+    cocina_object.externalIdentifier
+  end
+
+  def workspace
+    @workspace ||= DruidTools::Druid.new(druid, Settings.sdr.local_workspace_root)
+  end
+
+  def new_version_id
+    @new_version_id ||= signature_catalog.version_id + 1
+  end
 end
diff --git a/spec/services/preservation_ingest_service_spec.rb b/spec/services/preservation_ingest_service_spec.rb
index 4b86abc04..89a6f832c 100644
--- a/spec/services/preservation_ingest_service_spec.rb
+++ b/spec/services/preservation_ingest_service_spec.rb
@@ -11,6 +11,8 @@
       File.read(fixtures.join('sdr_repo/dd116zh0343/v0001/manifests/signatureCatalog.xml'))
     )
   end
+  let(:cocina_object) { instance_double(Cocina::Models::DRO, externalIdentifier: druid) }
+  let(:druid) { 'druid:dd116zh0343' }
 
   before do
     allow(Settings.sdr).to receive_messages(local_workspace_root: fixtures.join('workspace').to_s,
@@ -36,8 +38,6 @@
   end
 
   describe '.transfer' do
-    let(:druid) { 'druid:dd116zh0343' }
-    let(:cocina_object) { instance_double(Cocina::Models::DRO, externalIdentifier: druid) }
     let(:metadata_dir) { fixtures.join('workspace/dd/116/zh/0343/dd116zh0343/metadata') }
 
     before do
@@ -109,8 +109,8 @@
     end
   end
 
-  describe '.signature_catalog_from_preservation' do
-    let(:druid) { 'druid:dd116zh0343' }
+  describe '.signature_catalog' do
+    let(:service) { described_class.new(cocina_object) }
 
     context 'when signature_catalog exists in preservation' do
       before do
@@ -118,7 +118,7 @@
       end
 
       it 'retrieves it as a Moab::SignatureCatalog object' do
-        sig_cat = described_class.signature_catalog_from_preservation(druid)
+        sig_cat = service.send(:signature_catalog)
         expect(sig_cat).to be_an_instance_of(Moab::SignatureCatalog)
         expect(sig_cat.digital_object_id).to eq druid
         expect(sig_cat.version_id).to eq 1
@@ -132,7 +132,7 @@
       end
 
       it 'returns a Moab::SignatureCatalog object for version 0' do
-        sig_cat = described_class.signature_catalog_from_preservation(druid)
+        sig_cat = service.send(:signature_catalog)
         expect(sig_cat).to be_an_instance_of(Moab::SignatureCatalog)
         expect(sig_cat.digital_object_id).to eq druid
         expect(sig_cat.version_id).to eq 0
@@ -141,14 +141,20 @@
     end
   end
 
-  specify '.verify_version_id' do
-    expect(described_class.verify_version_id('/mypath/myfile', 2, 2)).to be_truthy
-    expect { described_class.verify_version_id('/mypath/myfile', 1, 2) }.to raise_exception('Version mismatch in /mypath/myfile, expected 1, found 2')
+  describe '.verify_version_id' do
+    let(:service) { described_class.new(cocina_object) }
+
+    it 'verifies the version' do
+      expect(service.send(:verify_version_id, '/mypath/myfile', 2, 2)).to be_truthy
+      expect { service.send(:verify_version_id, '/mypath/myfile', 1, 2) }.to raise_exception('Version mismatch in /mypath/myfile, expected 1, found 2')
+    end
   end
 
-  specify '.vmfile_version_id' do
-    metadata_dir = fixtures.join('workspace/dd/116/zh/0343/dd116zh0343/metadata')
-    vmfile = metadata_dir.join('versionMetadata.xml')
-    expect(described_class.vmfile_version_id(vmfile)).to eq 2
+  describe '.vmfile_version_id' do
+    it 'returns the version' do
+      metadata_dir = fixtures.join('workspace/dd/116/zh/0343/dd116zh0343/metadata')
+      vmfile = metadata_dir.join('versionMetadata.xml')
+      expect(described_class.new(cocina_object).send(:vmfile_version_id, vmfile)).to eq 2
+    end
   end
 end