ISO: Butcher school marinade

Years ago, we use to go to a butcher shop in Toledo to buy meat. It was quite inexpensive since it was cut by students and couldn’t be sold at top prices.
When you picked out your steaks, they asked you if you wanted it tenderized before wrapping. If you said yes, they swished it through a big vat of a tenderizing marinade.
Does anyone have any idea what this marinade was?