Brewing

Brewing is the process of creating potions and splash potions by adding various ingredients to water bottles in a brewing stand.

Potion Damage Values

The potion damage values represent a bit field that determines the properties and display name of a potion.

Display Name	Effect	Value	Bit(s)
-	Determines the potion effect	0-15	0-3
Awkward Potion	Allows addition of a main ingredient	16	4
Thick Potion	Turns potion to level II	32	5
Mundane Potion	Extends the potion duration	64	6
Mundane Potion	Normal potion	8192	13
Mundane Potion	Turns potion to splash	16384	14

By using a command, a potion with any of the above properties can be constructed (without the use of NBT-data).  E.g. a Speed Potion that is both extended and level II can be obtained with the command:

/give @p minecraft:potion 1 98

where the damage value 98 comes from 64 (for the extension) + 32 (for level II) + 2 (for speed).

The lowest 4 bits determine the potion effect (there can only be one).

Potion Effect	Potion Value (lowest 4 bits)	Effect ID
None	0	-
Regeneration	1	10
Swiftness	2	1
Fire Resistance	3	12
Poison	4	19
Health	5	6
Night Vision	6	16
Clear	7	-
Weakness	8	18
Strength	9	5
Slowness	10	2
Leaping	11	8
Harming	12	7
Water Breathing	13	13
Invisibility	14	14
Clear	15	-

Ingredients can be added to potions that meet certain requirements, when the potion damage value is changed accordingly.

• Nether Wart: can only be added to a water bottle (potion with damage value 0). It sets bit 4 (16), which allows a main ingredient[2] to be added to the potion.
• Glowstone: can always be added. Sets bit 5 (32) and clears bit 6 (64), which makes the potion a level II and resets the extension.
• Redstone: can always be added. Sets bit 6 (64) and clears bit 5 (32), which makes the potion extended and resets the level to I.
• Gunpowder: can only be added if bit 13 (8192), indicating a normal potion, is set. It sets bit 14 (16384) and clears bit 13 (8192). 
• Main ingredients: can be added if bit 4 (16) is set. Sets the lowest 4 bits acording to its effect type and sets bit 13 (8192) to indecate a normal potion.
• Fermented Spider Eye: can be added to most potions[check], altering the lowest 4 bits to change the effect type and sets bit 13 (8192) to indecate a normal potion.

[2] Main ingredients refers to any of: Ghast Tear, Sugar, Magma Cream, Spider Eye, Glistering Melon, Golden Carrot, Blaze Powder, Rabbit's Foot or Pufferfish.

Witch Drops

Witches can drop 4 types of potions, 3 of which have unusual damage values. They are a rare drop that can only drop while the witch is drinking the corresponding potion and if killed by a player. The chance for a potion drop is increased by the Looting enchantment.

Potion	Damage Value	Combination
Instant Health	16341	8192+Unused+64+16+5
Speed	16274	8192+Unused+16+2
Fire Resistance	16307	8192+Unused+32+16+3
Water Breathing	8237	8192+32+13

Brewing without Nether Wart

The Instant Health, Speed and Fire Resistance potions that witches drop have their bit (4) 16 set, which allows a further main ingredient to be added. This makes them usable as a replacement for awkward potions. It also means that all the potion types can be brewed on maps like SkyBlock, without the need of Nether Wart. Furthermore, the Instant Health potion is extended, and the Fire Resistance potion is a level II potion. This is otherwise unobtainable without commands. These properties have no effect by themselves, however, they are kept when a new ingredient is added. E.g. an Instant Health Potion + Sugar makes an extended Speed Potion.

Automatic Brewing

Stacked glass bottles can be shift-clicked into a brewing stand. If the right amount of glass bottles is put into a brewing stand using this method, it is possible for comparators to detect the difference between an ingredient being in the brewing stand, and no ingredient being in the brewing stand. This makes automatic systems easier, however it has the disadvantage, that only two potions can be brewed with each ingredient, since the third slot is taken up by emtpy glass bottles.