Affentor Schänke is another great example of the Apfelwein restaurants that can be found in the south part of the city. Affentor Schänke is probably a bit calmer than other restaurants of the same style.
Its environment is also rather familiar, and the waiters are the nicest I have interacted with. Also here you will be able to try Apfelwein and savour the most typically-Frankfurter dishes. Keep an eye out for seasonal offers (in November, for instance, starts the Goose season), which are a special way of tasting even more particular dishes.
In Affentor Schänke you will be able to try all the local specialities such as Handkäse (a specific kind of cheese marinated in vinegar), several kinds of Wurst and Grüne Soße (green sauce). If you would like to enjoy the environment but are not so much into the German cuisine, there are also tasty salads on offer and even two vegetarian dishes. The Käsesptätzle (a kind of noodles made with cheese and onions) are also a rather typical dish.
What I like the most about Affentor Schänke is their terrace, right in front of the restaurant. In Summer you can enjoy the liveliest of environments, and get a better feeling for the Sachsenhausen vibe than if you were indoors.