Test with stuff + Forestry potential support

BM_src/forestry/api/recipes/IVariableFermentable.java

@@ -0,0 +1,16 @@
+package forestry.api.recipes;
+
+import net.minecraft.item.ItemStack;
+
+/**
+ * Fermenter checks any valid fermentation item for an implementation of this interface.
+ * This does not supersede adding a proper recipe to the fermenter!
+ */
+public interface IVariableFermentable {
+	
+	/**
+	 * @param itemstack
+	 * @return Float representing the modification to be applied to the matching recipe's biomass output.
+	 */
+	float getFermentationModifier(ItemStack itemstack);
+}