diff --git a/docling_serve/docling_conversion.py b/docling_serve/docling_conversion.py
index 257b9f2..aee2c76 100644
--- a/docling_serve/docling_conversion.py
+++ b/docling_serve/docling_conversion.py
@@ -265,7 +265,7 @@ ConvertDocumentsRequest = Union[
 
 
 # Document converters will be preloaded and stored in a dictionary
-converters: Dict[str, DocumentConverter] = {}
+converters: Dict[bytes, DocumentConverter] = {}
 
 
 # Custom serializer for PdfFormatOption
@@ -301,7 +301,7 @@ def _serialize_pdf_format_option(pdf_format_option: PdfFormatOption) -> str:
 # Computes the PDF pipeline options and returns the PdfFormatOption and its hash
 def get_pdf_pipeline_opts(  # noqa: C901
     request: ConvertDocumentsOptions,
-) -> Tuple[PdfFormatOption, str]:
+) -> Tuple[PdfFormatOption, bytes]:
     if request.ocr_engine == OcrEngine.EASYOCR:
         try:
             import easyocr  # noqa: F401
@@ -401,7 +401,7 @@ def get_pdf_pipeline_opts(  # noqa: C901
 
     serialized_data = _serialize_pdf_format_option(pdf_format_option)
 
-    options_hash = hashlib.sha1(serialized_data.encode()).hexdigest()
+    options_hash = hashlib.sha1(serialized_data.encode()).digest()
 
     return pdf_format_option, options_hash