diff --git a/scrapy/exporters.py b/scrapy/exporters.py
index 7e1d01a0a..6f679480d 100644
--- a/scrapy/exporters.py
+++ b/scrapy/exporters.py
@@ -38,7 +38,7 @@ class BaseItemExporter(object):
         raise NotImplementedError
 
     def serialize_field(self, field, name, value):
-        serializer = field.get('serializer', self._to_str_if_unicode)
+        serializer = field.get('serializer', lambda x: x)
         return serializer(value)
 
     def start_exporting(self):
@@ -47,9 +47,6 @@ class BaseItemExporter(object):
     def finish_exporting(self):
         pass
 
-    def _to_str_if_unicode(self, value):
-        return value.encode(self.encoding) if isinstance(value, unicode) else value
-
     def _get_serialized_fields(self, item, default_value=None, include_empty=None):
         """Return the fields to export as an iterable of tuples
         (name, serialized_value)
@@ -89,7 +86,7 @@ class JsonLinesItemExporter(BaseItemExporter):
         self.file.write(self.encoder.encode(itemdict) + '\n')
 
 
-class JsonItemExporter(JsonLinesItemExporter):
+class JsonItemExporter(BaseItemExporter):
 
     def __init__(self, file, **kwargs):
         self._configure(kwargs, dont_fail=True)
@@ -170,13 +167,17 @@ class CsvItemExporter(BaseItemExporter):
         self._headers_not_written = True
         self._join_multivalued = join_multivalued
 
+    def serialize_field(self, field, name, value):
+        serializer = field.get('serializer', self._to_str_if_unicode)
+        return serializer(value)
+
     def _to_str_if_unicode(self, value):
         if isinstance(value, (list, tuple)):
             try:
                 value = self._join_multivalued.join(value)
             except TypeError:  # list in value may not contain strings
                 pass
-        return super(CsvItemExporter, self)._to_str_if_unicode(value)
+        return value.encode(self.encoding) if isinstance(value, unicode) else value
 
     def export_item(self, item):
         if self._headers_not_written:
@@ -251,7 +252,7 @@ class PythonItemExporter(BaseItemExporter):
             return dict(self._serialize_dict(value))
         if hasattr(value, '__iter__'):
             return [self._serialize_value(v) for v in value]
-        return self._to_str_if_unicode(value)
+        return value.encode(self.encoding) if isinstance(value, unicode) else value
 
     def _serialize_dict(self, value):
         for key, val in six.iteritems(value):
diff --git a/tests/test_exporters.py b/tests/test_exporters.py
index b24633959..c84fb978a 100644
--- a/tests/test_exporters.py
+++ b/tests/test_exporters.py
@@ -23,7 +23,7 @@ class TestItem(Item):
 class BaseItemExporterTest(unittest.TestCase):
 
     def setUp(self):
-        self.i = TestItem(name=u'John\xa3', age='22')
+        self.i = TestItem(name=u'John\xa3', age=u'22')
         self.output = BytesIO()
         self.ie = self._get_exporter()
 
@@ -55,6 +55,42 @@ class BaseItemExporterTest(unittest.TestCase):
         self.assertItemExportWorks(dict(self.i))
 
     def test_serialize_field(self):
+        res = self.ie.serialize_field(self.i.fields['name'], 'name', self.i['name'])
+        self.assertEqual(res, u'John\xa3')
+
+        res = self.ie.serialize_field(self.i.fields['age'], 'age', self.i['age'])
+        self.assertEqual(res, u'22')
+
+    def test_fields_to_export(self):
+        ie = self._get_exporter(fields_to_export=['name'])
+        self.assertEqual(list(ie._get_serialized_fields(self.i)), [('name', u'John\xa3')])
+
+    def test_field_custom_serializer(self):
+        def custom_serializer(value):
+            return str(int(value) + 2)
+
+        class CustomFieldItem(Item):
+            name = Field()
+            age = Field(serializer=custom_serializer)
+
+        i = CustomFieldItem(name=u'John\xa3', age=u'22')
+
+        ie = self._get_exporter()
+        self.assertEqual(ie.serialize_field(i.fields['name'], 'name', i['name']), u'John\xa3')
+        self.assertEqual(ie.serialize_field(i.fields['age'], 'age', i['age']), '24')
+
+
+class MidRefactoringBaseItemExporterTest(BaseItemExporterTest):
+    """Class introduced just to keep old behavior of BaseItemExporterTest for the
+    test cases that inherit from it while we make changes to exporters one by
+    one -- a needed refactoring trick because the test cases are quite coupled.
+
+    When we're done with the changes, we'll have ditched this class.
+    """
+    def test_serialize_field(self):
+        if self.ie.__class__ is BaseItemExporter:
+            return
+
         res = self.ie.serialize_field(self.i.fields['name'], 'name', self.i['name'])
         self.assertEqual(res, 'John\xc2\xa3')
 
@@ -62,6 +98,9 @@ class BaseItemExporterTest(unittest.TestCase):
         self.assertEqual(res, '22')
 
     def test_fields_to_export(self):
+        if self.ie.__class__ is BaseItemExporter:
+            return
+
         ie = self._get_exporter(fields_to_export=['name'])
         self.assertEqual(list(ie._get_serialized_fields(self.i)), [('name', 'John\xc2\xa3')])
 
@@ -71,6 +110,9 @@ class BaseItemExporterTest(unittest.TestCase):
         self.assertEqual(name, 'John\xa3')
 
     def test_field_custom_serializer(self):
+        if self.ie.__class__ is BaseItemExporter:
+            return
+
         def custom_serializer(value):
             return str(int(value) + 2)
 
@@ -85,7 +127,7 @@ class BaseItemExporterTest(unittest.TestCase):
         self.assertEqual(ie.serialize_field(i.fields['age'], 'age', i['age']), '24')
 
 
-class PythonItemExporterTest(BaseItemExporterTest):
+class PythonItemExporterTest(MidRefactoringBaseItemExporterTest):
     def _get_exporter(self, **kwargs):
         return PythonItemExporter(**kwargs)
 
@@ -152,7 +194,7 @@ class PickleItemExporterTest(BaseItemExporterTest):
         self.assertEqual(pickle.load(f), i2)
 
 
-class CsvItemExporterTest(BaseItemExporterTest):
+class CsvItemExporterTest(MidRefactoringBaseItemExporterTest):
 
     def _get_exporter(self, **kwargs):
         return CsvItemExporter(self.output, **kwargs)