diff --git a/src/stactools/ecmwf_forecast/stac.py b/src/stactools/ecmwf_forecast/stac.py
index 993b91b..9f1f0b2 100644
--- a/src/stactools/ecmwf_forecast/stac.py
+++ b/src/stactools/ecmwf_forecast/stac.py
@@ -211,35 +211,6 @@ def create_collection(
             {
                 "type": GRIB2_MEDIA_TYPE,
                 "roles": ["data"],
-                "extra_fields": {"kerchunk:indices": {'refs': {'step/0': 'base64:AAAAAAAAXkA=',
-  '.zattrs': '{"GRIB_centre":"ecmf","GRIB_centreDescription":"European Centre for Medium-Range Weather Forecasts","GRIB_edition":2,"GRIB_subCentre":0,"coordinates":"meanSea latitude longitude step time valid_time","institution":"European Centre for Medium-Range Weather Forecasts"}',
-  '.zgroup': '{"zarr_format":2}',
-  'meanSea/0': 'base64:AAAAAAAAAAA=',
-  'latitude/0': 'base64:AAAAAACAVkCamZmZmZlWwJqZmZmZmdm/',
-  'longitude/0': 'base64:AAAAAACAZsAAAAAAAIBmQJqZmZmZmdk/',
-  'mp2/.zarray': '{"chunks":[1,451,900],"compressor":null,"dtype":"<f8","fill_value":null,"filters":[{"dtype":"float64","id":"grib","var":"mp2"}],"order":"C","shape":[1,451,900],"zarr_format":2}',
-  'mp2/.zattrs': '{"GRIB_NV":0,"GRIB_Nx":900,"GRIB_Ny":451,"GRIB_cfName":"unknown","GRIB_cfVarName":"mp2","GRIB_dataType":"fc","GRIB_gridDefinitionDescription":"Latitude\\/longitude","GRIB_gridType":"regular_ll","GRIB_iDirectionIncrementInDegrees":0.4,"GRIB_iScansNegatively":0,"GRIB_jDirectionIncrementInDegrees":0.4,"GRIB_jPointsAreConsecutive":0,"GRIB_jScansPositively":0,"GRIB_latitudeOfFirstGridPointInDegrees":90.0,"GRIB_latitudeOfLastGridPointInDegrees":-90.0,"GRIB_longitudeOfFirstGridPointInDegrees":180.0,"GRIB_longitudeOfLastGridPointInDegrees":179.6,"GRIB_missingValue":3.4028234663852886e+38,"GRIB_name":"Mean zero-crossing wave period","GRIB_numberOfPoints":405900,"GRIB_paramId":140221,"GRIB_shortName":"mp2","GRIB_stepType":"instant","GRIB_stepUnits":1,"GRIB_typeOfLevel":"meanSea","GRIB_units":"s","_ARRAY_DIMENSIONS":["time","latitude","longitude"],"long_name":"Mean zero-crossing wave period","standard_name":"unknown","units":"s"}',
-  'mwd/.zarray': '{"chunks":[1,451,900],"compressor":null,"dtype":"<f8","fill_value":null,"filters":[{"dtype":"float64","id":"grib","var":"mwd"}],"order":"C","shape":[1,451,900],"zarr_format":2}',
-  'mwd/.zattrs': '{"GRIB_NV":0,"GRIB_Nx":900,"GRIB_Ny":451,"GRIB_cfName":"unknown","GRIB_cfVarName":"mwd","GRIB_dataType":"fc","GRIB_gridDefinitionDescription":"Latitude\\/longitude","GRIB_gridType":"regular_ll","GRIB_iDirectionIncrementInDegrees":0.4,"GRIB_iScansNegatively":0,"GRIB_jDirectionIncrementInDegrees":0.4,"GRIB_jPointsAreConsecutive":0,"GRIB_jScansPositively":0,"GRIB_latitudeOfFirstGridPointInDegrees":90.0,"GRIB_latitudeOfLastGridPointInDegrees":-90.0,"GRIB_longitudeOfFirstGridPointInDegrees":180.0,"GRIB_longitudeOfLastGridPointInDegrees":179.6,"GRIB_missingValue":3.4028234663852886e+38,"GRIB_name":"Mean wave direction","GRIB_numberOfPoints":405900,"GRIB_paramId":140230,"GRIB_shortName":"mwd","GRIB_stepType":"instant","GRIB_stepUnits":1,"GRIB_typeOfLevel":"meanSea","GRIB_units":"Degree true","_ARRAY_DIMENSIONS":["time","latitude","longitude"],"long_name":"Mean wave direction","standard_name":"unknown","units":"Degree true"}',
-  'mwp/.zarray': '{"chunks":[1,451,900],"compressor":null,"dtype":"<f8","fill_value":null,"filters":[{"dtype":"float64","id":"grib","var":"mwp"}],"order":"C","shape":[1,451,900],"zarr_format":2}',
-  'mwp/.zattrs': '{"GRIB_NV":0,"GRIB_Nx":900,"GRIB_Ny":451,"GRIB_cfName":"unknown","GRIB_cfVarName":"mwp","GRIB_dataType":"fc","GRIB_gridDefinitionDescription":"Latitude\\/longitude","GRIB_gridType":"regular_ll","GRIB_iDirectionIncrementInDegrees":0.4,"GRIB_iScansNegatively":0,"GRIB_jDirectionIncrementInDegrees":0.4,"GRIB_jPointsAreConsecutive":0,"GRIB_jScansPositively":0,"GRIB_latitudeOfFirstGridPointInDegrees":90.0,"GRIB_latitudeOfLastGridPointInDegrees":-90.0,"GRIB_longitudeOfFirstGridPointInDegrees":180.0,"GRIB_longitudeOfLastGridPointInDegrees":179.6,"GRIB_missingValue":3.4028234663852886e+38,"GRIB_name":"Mean wave period","GRIB_numberOfPoints":405900,"GRIB_paramId":140232,"GRIB_shortName":"mwp","GRIB_stepType":"instant","GRIB_stepUnits":1,"GRIB_typeOfLevel":"meanSea","GRIB_units":"s","_ARRAY_DIMENSIONS":["time","latitude","longitude"],"long_name":"Mean wave period","standard_name":"unknown","units":"s"}',
-  'swh/.zarray': '{"chunks":[1,451,900],"compressor":null,"dtype":"<f8","fill_value":null,"filters":[{"dtype":"float64","id":"grib","var":"swh"}],"order":"C","shape":[1,451,900],"zarr_format":2}',
-  'swh/.zattrs': '{"GRIB_NV":0,"GRIB_Nx":900,"GRIB_Ny":451,"GRIB_cfName":"unknown","GRIB_cfVarName":"swh","GRIB_dataType":"fc","GRIB_gridDefinitionDescription":"Latitude\\/longitude","GRIB_gridType":"regular_ll","GRIB_iDirectionIncrementInDegrees":0.4,"GRIB_iScansNegatively":0,"GRIB_jDirectionIncrementInDegrees":0.4,"GRIB_jPointsAreConsecutive":0,"GRIB_jScansPositively":0,"GRIB_latitudeOfFirstGridPointInDegrees":90.0,"GRIB_latitudeOfLastGridPointInDegrees":-90.0,"GRIB_longitudeOfFirstGridPointInDegrees":180.0,"GRIB_longitudeOfLastGridPointInDegrees":179.6,"GRIB_missingValue":3.4028234663852886e+38,"GRIB_name":"Significant height of combined wind waves and swell","GRIB_numberOfPoints":405900,"GRIB_paramId":140229,"GRIB_shortName":"swh","GRIB_stepType":"instant","GRIB_stepUnits":1,"GRIB_typeOfLevel":"meanSea","GRIB_units":"m","_ARRAY_DIMENSIONS":["time","latitude","longitude"],"long_name":"Significant height of combined wind waves and swell","standard_name":"unknown","units":"m"}',
-  'pp1d/.zarray': '{"chunks":[1,451,900],"compressor":null,"dtype":"<f8","fill_value":null,"filters":[{"dtype":"float64","id":"grib","var":"pp1d"}],"order":"C","shape":[1,451,900],"zarr_format":2}',
-  'pp1d/.zattrs': '{"GRIB_NV":0,"GRIB_Nx":900,"GRIB_Ny":451,"GRIB_cfName":"unknown","GRIB_cfVarName":"pp1d","GRIB_dataType":"fc","GRIB_gridDefinitionDescription":"Latitude\\/longitude","GRIB_gridType":"regular_ll","GRIB_iDirectionIncrementInDegrees":0.4,"GRIB_iScansNegatively":0,"GRIB_jDirectionIncrementInDegrees":0.4,"GRIB_jPointsAreConsecutive":0,"GRIB_jScansPositively":0,"GRIB_latitudeOfFirstGridPointInDegrees":90.0,"GRIB_latitudeOfLastGridPointInDegrees":-90.0,"GRIB_longitudeOfFirstGridPointInDegrees":180.0,"GRIB_longitudeOfLastGridPointInDegrees":179.6,"GRIB_missingValue":3.4028234663852886e+38,"GRIB_name":"Peak wave period","GRIB_numberOfPoints":405900,"GRIB_paramId":140231,"GRIB_shortName":"pp1d","GRIB_stepType":"instant","GRIB_stepUnits":1,"GRIB_typeOfLevel":"meanSea","GRIB_units":"s","_ARRAY_DIMENSIONS":["time","latitude","longitude"],"long_name":"Peak wave period","standard_name":"unknown","units":"s"}',
-  'step/.zarray': '{"chunks":[1],"compressor":null,"dtype":"<f8","fill_value":null,"filters":null,"order":"C","shape":[1],"zarr_format":2}',
-  'step/.zattrs': '{"_ARRAY_DIMENSIONS":["time"],"long_name":"time since forecast_reference_time","standard_name":"forecast_period","units":"hours"}',
-  'time/.zarray': '{\n    "chunks": [\n        1\n    ],\n    "compressor": null,\n    "dtype": "<i8",\n    "fill_value": null,\n    "filters": null,\n    "order": "C",\n    "shape": [\n        1\n    ],\n    "zarr_format": 2\n}',
-  'time/.zattrs': '{\n    "_ARRAY_DIMENSIONS": [\n        "time"\n    ],\n    "calendar": "proleptic_gregorian",\n    "long_name": "initial time of forecast",\n    "standard_name": "forecast_reference_time",\n    "units": "seconds since 1970-01-01T00:00:00"\n}',
-  'meanSea/.zarray': '{"chunks":[1],"compressor":null,"dtype":"<f8","fill_value":null,"filters":null,"order":"C","shape":[1],"zarr_format":2}',
-  'meanSea/.zattrs': '{"_ARRAY_DIMENSIONS":["time"]}',
-  'latitude/.zarray': '{"chunks":[451],"compressor":null,"dtype":"<f8","fill_value":null,"filters":[{"id": "range"}],"order":"C","shape":[451],"zarr_format":2}',
-  'latitude/.zattrs': '{"_ARRAY_DIMENSIONS":["latitude"],"long_name":"latitude","standard_name":"latitude","units":"degrees_north"}',
-  'longitude/.zarray': '{"chunks":[900],"compressor":null,"dtype":"<f8","fill_value":null,"filters":[{"id": "range"}],"order":"C","shape":[900],"zarr_format":2}',
-  'longitude/.zattrs': '{"_ARRAY_DIMENSIONS":["longitude"],"long_name":"longitude","standard_name":"longitude","units":"degrees_east"}',
-  'valid_time/.zarray': '{"chunks":[1],"compressor":null,"dtype":"<i8","fill_value":null,"filters":null,"order":"C","shape":[1],"zarr_format":2}',
-  'valid_time/.zattrs': '{"_ARRAY_DIMENSIONS":["time"],"calendar":"proleptic_gregorian","long_name":"time","standard_name":"time","units":"seconds since 1970-01-01T00:00:00"}'},
- 'version': 1}}, 
                 "title": "GRIB2 data file",
                 "description": (
                     "The forecast data, as a grib2 file. Subsets of the data can be loaded "
@@ -432,7 +403,7 @@ def _create_item_from_parts(parts: list[Parts], split_by_step=False) -> Item:
                 p.filename,
                 media_type=media_type,
                 roles=roles,
-                extra_fields={"ecmwf:step": p.step, "kerchunk:indices:unique": kerchunk_indices} if not split_by_step else {"kerchunk:indices:unique": kerchunk_indices},
+                extra_fields={"ecmwf:step": p.step, "kerchunk:indices": kerchunk_indices} if not split_by_step else {"kerchunk:indices": kerchunk_indices},
             ),
         )