The Bioreactor is one of the most reliable methods for generating loads of power in Subnautica: Below Zero, but the best thing about it is that you can turn your otherwise useless moldy food into useful energy for your base.

Although repurposing old food and piles of fish into energy sounds great, there are actually some surprising differences in how much energy certain items provide. A Glow Whale egg, for example, provides more energy than a Shrub Nut. This list covers the best Bioreactor fuels in the game in order to help you maximize efficiency and let you know what you should keep your eyes open for while you explore.

Everything You Need To Know About The Bioreactor

Before diving into the list of the best Bioreactor fuels in Below Zero, here are all the details you need to know about the Bioreactor, including how to craft one, how it works, and how you can use it to generate loads of energy.

General tips:

  • Bioreactors have a maximum energy output of 500, which is enough to power a small base. They’re a good power source in areas where Solar Panels or Thermal Generators are not easy or reliable to use. Bioreactors can only be placed inside Multipurpose or Large Rooms. Pretty much any organic material can be placed inside the Bioreactor, including all of the game’s eggs, fish, moldy food, and plant life.

Building A Bioreactor

Unlike some other habitat modules and items in Below Zero, you don’t need to find the fragments for the Bioreactor out under the waves. You have access to the crafting recipe from the moment you unlock the Habitat Builder.

It requires:

  • 3 Titanium 1 Wiring Kit 1 Lubricant

How The Slots In The Bioreactor Work

To understand how to get the most power out of your Bioreactor, you’ve got to get your head around the slots. The Bioreactor has a 4x4 inventory. Different food items, fauna, and flora take up more slots depending on their size.

A Glow Whale, for example, fills the whole Bioreactor. It will generate an energy value of 840, which is four times more than its original 52.5 energy value. That’s 52.5 times four, times four again. It’s a bit complicated to begin with but easy to understand after using the Bioreactor a few times.

However, even though that sounds like lots of energy, each Bioreactor has a cap of 500 units. There are more efficient methods of powering your reactor rather than filling it with expensive, chunky fuel. Glow Whale isn’t exactly easy to come by, either.

Best Bioreactor Fuels In Subnautica: Below Zero

This list will break down the most efficient Bioreactor fuels in Below Zero, based on how easy they are to find or reproduce. It’s no good hunting for Peepers if you can have your own store of fish inside your base, for example. This can be done by either farming with Growbeds (for fruit) or placing down Alien Containment Units (for fish). Here are some of the best fuels to prioritize.

Marblemelon

The Marblemelon is originally found inside Marguerit’s Greenhouse but can be farmed quite easily inside your base. This is probably one of the best plants to grow for your Bioreactor. Here’s why.

  • The larger Marblemelon plant covers two slots and provides total energy of 420, almost enough to fill a Bioreactor to its 500 cap. You can use either a Marblemelon or a Small Marblemelon. They both have a total energy output of 280. Small Marblemelons take up less space. Marblemelon can be grown outdoors or indoors. You can set up a series of plant pots or shelves in the room with your Bioreactor for convenience.

Arctic Peeper

In terms of fauna, the Arctic Peeper is probably one of the most reliable Bioreactor fuel sources. The fish is extremely common in the oceans of 4546B. Each fish provides an energy value of 350 and only takes up one slot in the Bioreactor.

  • Peepers are reliable because you can find them in many starter biomes, such as the Twisty Bridges and Shallow Twisty Bridges. These are good areas to build your first base. Peepers can be farmed inside an Alien Containment Unit for a reliable source of fuel for the Bioreactor.

Nootfish

The Nootfish provides great value at 315 energy for each 1x1 slot. That means you can pretty much max out your Bioreactor’s energy cap with just one or two Nootfish. Although they’re not as common as the Peeper, the Nootfish is still a good option.

  • The Nootfish is found in the Lilypad Islands biome. Nootfish can quickly become a reliable source of energy if you farm them inside an Alien Containment Unit.

Fevered Pepper (Heat Fruit)

The Fevered Pepper arrives a bit later into the game’s cycle, but it’s still one of the best fuel sources if you have a reliable farm set up. These fruits cover a 1x2 slot in the Bioreactor and provide a total of 350 energy.

  • Fevered Peppers, originally called Heat Fruit, are found on Fevered Pepper Trees, typically in the Glacial Basin biome. They can be grown on indoor growbeds, ideal for your Bioreactor room. Fevered Peppers are also useful to have around the base as they can be used to craft Spicy Fruit Salad, one of the best foods in Subnautica: Below Zero.

Root Globules

In terms of pure energy value, Root Globules offer some of the best slots to energy ratio in the game: each Globule provides 700 energy in the Bioreactor. However, they are much rarer to find, and cannot be farmed by the player.

  • Located growing on the Arctic Kelp Cave Kelp Roots. Though they do provide a huge amount of energy, they are required to craft a piece of the Architect’s suit later in the game. You might want to save a couple.

NEXT: Subnautica: How To Build A Base On Land