Cut carrots however you like (spears, matchsticks). I prefer to have them cut into rounds.
Place carrots, garlic, serrano pepper and black peppercorns in quart-sized wide-mouth mason jar.
Add water and salt (brine) leaving about 2 inches of headroom.
Add whey (optional).
Using a glass weight (pickle pebble) and an airlock, allow to ferment for 3-4 days or until it is bubbling.
Store in the refrigerator for 6-9 months.