diff --git a/core/src/Brewing.cpp b/core/src/Brewing.cpp
new file mode 100644
index 0000000..3a9a38a
--- /dev/null
+++ b/core/src/Brewing.cpp
@@ -0,0 +1,154 @@
+#include "vf/Brewing.h"
+
+#include <algorithm>
+#include <cmath>
+
+namespace vf {
+
+namespace {
+
+using Ingredient = BrewRecipe::Ingredient;
+
+struct PotionProfile {
+    EffectKind kind = EffectKind::Count;
+    int baseTicks = 0;
+    int extendedTicks = 0;  // zero: redstone does nothing
+    int upgradedTicks = 0;  // zero: glowstone does nothing
+    int upgradedLevel = 1;
+};
+
+const PotionProfile& profileFor(PotionKind kind) {
+    static const PotionProfile profiles[] = {
+        {EffectKind::Count, 0, 0, 0, 1},                 // Water
+        {EffectKind::Count, 0, 0, 0, 1},                 // Mundane
+        {EffectKind::Count, 0, 0, 0, 1},                 // Thick
+        {EffectKind::Count, 0, 0, 0, 1},                 // Awkward
+        {EffectKind::InstantHealth, 1, 0, 1, 2},         // Healing
+        {EffectKind::InstantDamage, 1, 0, 1, 2},         // Harming
+        {EffectKind::Regeneration, 900, 1800, 440, 2},   // Regeneration
+        {EffectKind::Poison, 900, 1800, 432, 2},         // Poison
+        {EffectKind::Speed, 3600, 9600, 1800, 2},        // Swiftness
+        {EffectKind::Slowness, 1800, 4800, 400, 4},      // Slowness
+        {EffectKind::JumpBoost, 3600, 9600, 1800, 2},    // Leaping
+        {EffectKind::Strength, 3600, 9600, 1800, 2},     // Strength
+        {EffectKind::Weakness, 1800, 4800, 0, 1},        // Weakness
+        {EffectKind::FireResistance, 3600, 9600, 0, 1},  // FireResistance
+        {EffectKind::WaterBreathing, 3600, 9600, 0, 1},  // WaterBreathing
+        {EffectKind::NightVision, 3600, 9600, 0, 1},     // NightVision
+        {EffectKind::Invisibility, 3600, 9600, 0, 1},    // Invisibility
+    };
+    static_assert(sizeof(profiles) / sizeof(profiles[0]) ==
+                      static_cast<std::size_t>(PotionKind::Count),
+                  "potion profile table must cover every PotionKind");
+    return profiles[static_cast<std::size_t>(kind)];
+}
+
+bool applyModifier(PotionItem& potion, Ingredient ingredient) {
+    const PotionProfile& profile = profileFor(potion.kind);
+    switch (ingredient) {
+        case Ingredient::Glowstone:
+            if (profile.upgradedTicks == 0 || potion.upgraded) return false;
+            potion.upgraded = true;
+            potion.extended = false;
+            return true;
+        case Ingredient::Redstone:
+            if (profile.extendedTicks == 0 || potion.extended) return false;
+            potion.extended = true;
+            potion.upgraded = false;
+            return true;
+        case Ingredient::Gunpowder:
+            if (potion.form == PotionItem::Form::Splash) return false;
+            potion.form = PotionItem::Form::Splash;
+            return true;
+        default:
+            return false;
+    }
+}
+
+} // namespace
+
+const std::vector<BrewRecipe>& brewRecipes() {
+    static const std::vector<BrewRecipe> recipes = {
+        {PotionKind::Water, Ingredient::NetherWart, PotionKind::Awkward},
+        {PotionKind::Water, Ingredient::Glowstone, PotionKind::Thick},
+        {PotionKind::Water, Ingredient::Redstone, PotionKind::Mundane},
+        {PotionKind::Water, Ingredient::FermentedSpiderEye, PotionKind::Weakness},
+
+        {PotionKind::Awkward, Ingredient::Sugar, PotionKind::Swiftness},
+        {PotionKind::Awkward, Ingredient::GlisteringMelon, PotionKind::Healing},
+        {PotionKind::Awkward, Ingredient::SpiderEye, PotionKind::Poison},
+        {PotionKind::Awkward, Ingredient::BlazePowder, PotionKind::Strength},
+        {PotionKind::Awkward, Ingredient::MagmaCream, PotionKind::FireResistance},
+        {PotionKind::Awkward, Ingredient::PufferFish, PotionKind::WaterBreathing},
+        {PotionKind::Awkward, Ingredient::GoldenCarrot, PotionKind::NightVision},
+        {PotionKind::Awkward, Ingredient::GhastTear, PotionKind::Regeneration},
+        {PotionKind::Awkward, Ingredient::RabbitFoot, PotionKind::Leaping},
+
+        {PotionKind::NightVision, Ingredient::FermentedSpiderEye, PotionKind::Invisibility},
+        {PotionKind::Healing, Ingredient::FermentedSpiderEye, PotionKind::Harming},
+        {PotionKind::Poison, Ingredient::FermentedSpiderEye, PotionKind::Harming},
+        {PotionKind::Swiftness, Ingredient::FermentedSpiderEye, PotionKind::Slowness},
+        {PotionKind::Leaping, Ingredient::FermentedSpiderEye, PotionKind::Slowness},
+        {PotionKind::Strength, Ingredient::FermentedSpiderEye, PotionKind::Weakness},
+    };
+    return recipes;
+}
+
+PotionItem brewResult(const PotionItem& base, Ingredient ingredient, bool& changed) {
+    PotionItem brewed = base;
+    changed = false;
+    if (ingredient == Ingredient::None) return brewed;
+
+    for (const BrewRecipe& recipe : brewRecipes()) {
+        if (recipe.input != base.kind || recipe.ingredient != ingredient) continue;
+        brewed.kind = recipe.output;
+        brewed.upgraded = false;
+        brewed.extended = false;
+        changed = true;
+        return brewed;
+    }
+    changed = applyModifier(brewed, ingredient);
+    return brewed;
+}
+
+bool setBottle(BrewingStandState& stand, int slot, const PotionItem& potion) {
+    if (slot < 0 || slot >= brewingBottleSlots) return false;
+    BrewingSlot& bottle = stand.bottles[static_cast<std::size_t>(slot)];
+    if (bottle.occupied) return false;
+    bottle.potion = potion;
+    bottle.occupied = true;
+    stand.progressTicks = 0;
+    return true;
+}
+
+PotionItem takeBottle(BrewingStandState& stand, int slot, bool& taken) {
+    taken = false;
+    if (slot < 0 || slot >= brewingBottleSlots) return {};
+    BrewingSlot& bottle = stand.bottles[static_cast<std::size_t>(slot)];
+    if (!bottle.occupied) return {};
+    PotionItem removed = bottle.potion;
+    bottle = BrewingSlot{};
+    taken = true;
+    stand.progressTicks = 0;
+    return removed;
+}
+
+bool setIngredient(BrewingStandState& stand, Ingredient ingredient, int count) {
+    if (ingredient == Ingredient::None || count <= 0) return false;
+    if (stand.ingredientCount > 0 && stand.ingredient != ingredient) return false;
+    if (stand.ingredient == ingredient) {
+        stand.ingredientCount += count;
+        return true;
+    }
+    stand.ingredient = ingredient;
+    stand.ingredientCount = count;
+    stand.progressTicks = 0;
+    return true;
+}
+
+bool addFuel(BrewingStandState& stand, int blazePowderCount) {
+    if (blazePowderCount <= 0) return false;
+    stand.fuel += blazePowderCount * brewsPerBlazePowder;
+    return true;
+}
+