Elasticsearch German stemmer doesn't do plural

I'm working on a basic German analyzer in Elasticsearch which is defined as follows

{
  "settings": {
    "analysis": {
      "filter": {
        "german_stemmer": {
          "type": "snowball",
          "language": "German"
        },
        "german_stop": {
          "type": "stop",
          "stopwords": "_german_"
        }
      },
      "analyzer": {
        "german_search": {
          "filter": ["lowercase", "german_stop", "german_stemmer"],
          "tokenizer": "standard"
        }
      }
    }
  }
}

While testing it I realized that it is not dealing well with Kürbis and Kürbisse. Stemming those two words brings different output while from my understanding (just what I read online) Kurbis stands for Pumpkin and Kurbisse is Pumpkins. It looks like the stemmer is not dealing well with plurals.

Any ideas on how can I solve this?