diff --git a/src/unitxt/api.py b/src/unitxt/api.py
index 23de331bd4..3e66a2fc60 100644
--- a/src/unitxt/api.py
+++ b/src/unitxt/api.py
@@ -22,7 +22,7 @@
 from .logging_utils import get_logger
 from .metric_utils import EvaluationResults, _compute, _inference_post_process
 from .operator import SourceOperator
-from .schema import loads_batch
+from .schema import SerializeInstancesBeforeDump, loads_batch
 from .settings_utils import get_constants, get_settings
 from .standard import DatasetRecipe
 from .task import Task
@@ -204,7 +204,7 @@ def _source_to_dataset(
         )
         if split is not None:
             stream = {split: stream[split]}
-        ds_builder._generators = stream
+        ds_builder._generators = SerializeInstancesBeforeDump()(stream)
 
         try:
             ds_builder.download_and_prepare(
@@ -354,10 +354,12 @@ def produce(
     if not is_list:
         instance_or_instances = [instance_or_instances]
     dataset_recipe = _get_recipe_with_cache(dataset_query, **kwargs)
-    result = dataset_recipe.produce(instance_or_instances)
+    instances = dataset_recipe.produce(instance_or_instances)
+    serialize = SerializeInstancesBeforeDump()
+    instances = [serialize.process_instance(instance) for instance in instances]
     if not is_list:
-        return result[0]
-    return Dataset.from_list(result).with_transform(loads_batch)
+        return instances[0]
+    return Dataset.from_list(instances).with_transform(loads_batch)
 
 
 def infer(
diff --git a/src/unitxt/dataset.py b/src/unitxt/dataset.py
index 94529f42ff..1c207470fc 100644
--- a/src/unitxt/dataset.py
+++ b/src/unitxt/dataset.py
@@ -47,13 +47,14 @@
 from .random_utils import __file__ as _
 from .recipe import __file__ as _
 from .register import __file__ as _
-from .schema import loads_batch, loads_instance
+from .schema import SerializeInstancesBeforeDump, loads_batch, loads_instance
 from .serializers import __file__ as _
 from .settings_utils import get_constants
 from .span_lableing_operators import __file__ as _
 from .split_utils import __file__ as _
 from .splitters import __file__ as _
 from .standard import __file__ as _
+from .stream import MultiStream
 from .stream import __file__ as _
 from .stream_operators import __file__ as _
 from .string_operators import __file__ as _
@@ -92,7 +93,9 @@ def generators(self):
                 logger.info("Loading with huggingface unitxt copy...")
                 dataset = get_dataset_artifact(self.config.name)
 
-            self._generators = dataset()
+            multi_stream: MultiStream = dataset()
+
+            self._generators = SerializeInstancesBeforeDump()(multi_stream)
 
         return self._generators
 
diff --git a/src/unitxt/schema.py b/src/unitxt/schema.py
index 5926b120cc..21d2b72b5d 100644
--- a/src/unitxt/schema.py
+++ b/src/unitxt/schema.py
@@ -7,7 +7,7 @@
 from .artifact import Artifact
 from .dict_utils import dict_get
 from .image_operators import ImageDataString
-from .operator import InstanceOperatorValidator
+from .operator import InstanceOperator, InstanceOperatorValidator
 from .settings_utils import get_constants, get_settings
 from .type_utils import isoftype
 from .types import Image
@@ -68,6 +68,18 @@ def load_chat_source(chat_str):
     return chat
 
 
+class SerializeInstancesBeforeDump(InstanceOperator):
+    def process(
+        self, instance: Dict[str, Any], stream_name: Optional[str] = None
+    ) -> Dict[str, Any]:
+        if settings.task_data_as_text:
+            instance["task_data"] = json.dumps(instance["task_data"])
+
+        if not isinstance(instance["source"], str):
+            instance["source"] = json.dumps(instance["source"])
+        return instance
+
+
 def loads_batch(batch):
     if (
         "source" in batch
@@ -148,14 +160,6 @@ def _get_instance_task_data(
             task_data["__tools__"] = instance["__tools__"]
         return task_data
 
-    def serialize_instance_fields(self, instance, task_data):
-        if settings.task_data_as_text:
-            instance["task_data"] = json.dumps(task_data)
-
-        if not isinstance(instance["source"], str):
-            instance["source"] = json.dumps(instance["source"])
-        return instance
-
     def process(
         self, instance: Dict[str, Any], stream_name: Optional[str] = None
     ) -> Dict[str, Any]:
@@ -179,7 +183,7 @@ def process(
                 for instance in instance.pop(constants.demos_field)
             ]
 
-        instance = self.serialize_instance_fields(instance, task_data)
+        instance["task_data"] = task_data
 
         if self.remove_unnecessary_fields:
             keys_to_delete = []
@@ -224,7 +228,8 @@ def validate(self, instance: Dict[str, Any], stream_name: Optional[str] = None):
             instance, dict
         ), f"Instance should be a dict, got {type(instance)}"
         schema = get_schema(stream_name)
+
         assert all(
             key in instance for key in schema
-        ), f"Instance should have the following keys: {schema}. Instance is: {instance}"
-        schema.encode_example(instance)
+        ), f"Instance should have the following keys: {schema.keys()}. Instance is: {instance.keys()}"
+        # schema.encode_example(instance)