diff --git a/src/Echo/src/EchoTranslationEngine/TranslationEngineServiceV1.cs b/src/Echo/src/EchoTranslationEngine/TranslationEngineServiceV1.cs
index fb7abc66..6f40a621 100644
--- a/src/Echo/src/EchoTranslationEngine/TranslationEngineServiceV1.cs
+++ b/src/Echo/src/EchoTranslationEngine/TranslationEngineServiceV1.cs
@@ -82,9 +82,9 @@ await client.BuildStartedAsync(
                 try
                 {
                     List<InsertPretranslationsRequest> pretranslationsRequests = [];
-                    _parallelCorpusPreprocessingService.Preprocess(
+                    await _parallelCorpusPreprocessingService.Preprocess(
                         request.Corpora.Select(Map).ToList(),
-                        row => { },
+                        row => Task.CompletedTask,
                         (row, corpus) =>
                         {
                             pretranslationsRequests.Add(
diff --git a/src/Machine/src/Serval.Machine.Shared/Services/PreprocessBuildJob.cs b/src/Machine/src/Serval.Machine.Shared/Services/PreprocessBuildJob.cs
index eebdfcff..e3c31328 100644
--- a/src/Machine/src/Serval.Machine.Shared/Services/PreprocessBuildJob.cs
+++ b/src/Machine/src/Serval.Machine.Shared/Services/PreprocessBuildJob.cs
@@ -94,25 +94,27 @@ CancellationToken cancellationToken
         if (buildOptions is not null)
             buildOptionsObject = JsonSerializer.Deserialize<JsonObject>(buildOptions);
 
-        using MemoryStream sourceStream = new();
-        using MemoryStream targetStream = new();
-        using MemoryStream pretranslationStream = new();
-
-        using StreamWriter targetTrainWriter = new(targetStream, Encoding.Default);
-        using StreamWriter sourceTrainWriter = new(sourceStream, Encoding.Default);
-        await using Utf8JsonWriter pretranslateWriter = new(pretranslationStream, PretranslateWriterOptions);
+        await using StreamWriter sourceTrainWriter =
+            new(await _sharedFileService.OpenWriteAsync($"builds/{buildId}/train.src.txt", cancellationToken));
+        await using StreamWriter targetTrainWriter =
+            new(await _sharedFileService.OpenWriteAsync($"builds/{buildId}/train.trg.txt", cancellationToken));
+        await using Utf8JsonWriter pretranslateWriter =
+            new(
+                await _sharedFileService.OpenWriteAsync($"builds/{buildId}/pretranslate.src.json", cancellationToken),
+                PretranslateWriterOptions
+            );
 
         int trainCount = 0;
         int pretranslateCount = 0;
         pretranslateWriter.WriteStartArray();
-        _parallelCorpusPreprocessingService.Preprocess(
+        await _parallelCorpusPreprocessingService.Preprocess(
             corpora,
-            row =>
+            async row =>
             {
                 if (row.SourceSegment.Length > 0 || row.TargetSegment.Length > 0)
                 {
-                    sourceTrainWriter.WriteLine(row.SourceSegment);
-                    targetTrainWriter.WriteLine(row.TargetSegment);
+                    await sourceTrainWriter.WriteLineAsync(row.SourceSegment);
+                    await targetTrainWriter.WriteLineAsync(row.TargetSegment);
                 }
                 if (row.SourceSegment.Length > 0 && row.TargetSegment.Length > 0)
                     trainCount++;
@@ -138,22 +140,6 @@ CancellationToken cancellationToken
 
         pretranslateWriter.WriteEndArray();
 
-        await sourceTrainWriter.FlushAsync(cancellationToken);
-        await targetTrainWriter.FlushAsync(cancellationToken);
-        await pretranslateWriter.FlushAsync(cancellationToken);
-
-        async Task WriteStreamAsync(MemoryStream stream, string path)
-        {
-            stream.Position = 0;
-            await using StreamWriter writer = new(await _sharedFileService.OpenWriteAsync(path, cancellationToken));
-            await writer.WriteAsync(Encoding.Default.GetString(stream.ToArray()));
-            await writer.FlushAsync(cancellationToken);
-        }
-
-        await WriteStreamAsync(sourceStream, $"builds/{buildId}/train.src.txt");
-        await WriteStreamAsync(targetStream, $"builds/{buildId}/train.trg.txt");
-        await WriteStreamAsync(pretranslationStream, $"builds/{buildId}/pretranslate.src.json");
-
         return (trainCount, pretranslateCount);
     }
 
diff --git a/src/ServiceToolkit/src/SIL.ServiceToolkit/Services/IParallelCorpusPreprocessingService.cs b/src/ServiceToolkit/src/SIL.ServiceToolkit/Services/IParallelCorpusPreprocessingService.cs
index 1556de6d..d1fcf6a7 100644
--- a/src/ServiceToolkit/src/SIL.ServiceToolkit/Services/IParallelCorpusPreprocessingService.cs
+++ b/src/ServiceToolkit/src/SIL.ServiceToolkit/Services/IParallelCorpusPreprocessingService.cs
@@ -1,10 +1,12 @@
+using Nito.AsyncEx;
+
 namespace SIL.ServiceToolkit.Utils;
 
 public interface IParallelCorpusPreprocessingService
 {
-    void Preprocess(
+    Task Preprocess(
         IReadOnlyList<ParallelCorpus> corpora,
-        Action<Row> train,
+        Func<Row, Task> train,
         Action<Row, ParallelCorpus> pretranslate,
         bool useKeyTerms = false
     );
diff --git a/src/ServiceToolkit/src/SIL.ServiceToolkit/Services/ParallelCorpusPreprocessingService.cs b/src/ServiceToolkit/src/SIL.ServiceToolkit/Services/ParallelCorpusPreprocessingService.cs
index e75a2d59..7e1d9aae 100644
--- a/src/ServiceToolkit/src/SIL.ServiceToolkit/Services/ParallelCorpusPreprocessingService.cs
+++ b/src/ServiceToolkit/src/SIL.ServiceToolkit/Services/ParallelCorpusPreprocessingService.cs
@@ -25,9 +25,9 @@ internal int Seed
         }
     }
 
-    public void Preprocess(
+    public async Task Preprocess(
         IReadOnlyList<ParallelCorpus> corpora,
-        Action<Row> train,
+        Func<Row, Task> train,
         Action<Row, ParallelCorpus> pretranslate,
         bool useKeyTerms = false
     )
@@ -77,7 +77,7 @@ public void Preprocess(
 
             foreach (Row row in CollapseRanges(trainingRows))
             {
-                train(row);
+                await train(row);
             }
 
             if (useKeyTerms)
@@ -93,7 +93,7 @@ public void Preprocess(
                     IParallelTextCorpus parallelKeyTermsCorpus = sourceTermCorpus.AlignRows(targetTermCorpus);
                     foreach (ParallelTextRow row in parallelKeyTermsCorpus)
                     {
-                        train(new Row(row.TextId, row.Refs, row.SourceText, row.TargetText, 1));
+                        await train(new Row(row.TextId, row.Refs, row.SourceText, row.TargetText, 1));
                     }
                 }
             }
diff --git a/src/ServiceToolkit/test/SIL.ServiceToolkit.Tests/Services/ParallelCorpusProcessingServiceTests.cs b/src/ServiceToolkit/test/SIL.ServiceToolkit.Tests/Services/ParallelCorpusProcessingServiceTests.cs
index 543332e2..a58d891b 100644
--- a/src/ServiceToolkit/test/SIL.ServiceToolkit.Tests/Services/ParallelCorpusProcessingServiceTests.cs
+++ b/src/ServiceToolkit/test/SIL.ServiceToolkit.Tests/Services/ParallelCorpusProcessingServiceTests.cs
@@ -79,6 +79,7 @@ public void TestParallelCorpusPreprocessor()
             {
                 if (row.SourceSegment.Length > 0 && row.TargetSegment.Length > 0)
                     trainCount++;
+                return Task.CompletedTask;
             },
             (row, _) =>
             {