Encourage your desired behavior
It doesn't sound like you want to explicitly disallow the alchemy jug, just make sure it's not being overused. As a GM, you have a variety of tools you can use to encourage other behavior.
Descriptions, descriptions, descriptions
There are at least two situations that you can describe that will help encourage variety among your players.
- Describe meal time for the characters
When describing meal time, highlight the monotony of the alchemy jug approach. It is the same meal time and time again. The players are bound to get tired of hearing the same description time and time again.
- Describe the smells that characters encounter
When you are describing an area, make sure to pull in the smells and tastes that the characters will encounter. Encountering an NPC at a campsite should include the smells of rabbit roasting on the fire. Walking through the forest, you may smell droppings indicating good hunting grounds. Entering an inn, you can smell the scent of pies wafting in from the kitchen. A hearty description of food that they see can further encourage a desire for real food.
Remember that you can award inspiration to reward good roleplaying. Consider rewarding inspiration if there is a fight about the monotony of the alchemy jug approach.
Add NPCs to the group
Either through a rescue or escort mission or random encounter, grow the party size to make the alchemy jug approach not feasible. They will have to rely on using additional means for sustaining themselves and their NPC companions. This may be through the Create Food and Water spell or Goodberries or hunting.
NPCs encountering the party will probably notice the lack of rations being carried by the party and get curious. If the party is not being discrete with their jug, it may very well draw questions on what the jug does and encourage them to show off the jugs properties. In the wilderness, it will be a valuable commodity and could draw some attention from the more unsavory types as well.
Dead magic zones
The party may find zones of dead magic on their travels. Magical items have their properties suppressed when in this area. I would use this sparingly given the artificers reliance on magic items, but it would be a nasty surprise to find their jug isn't working.
Add food/water to the items found while looting or when completing encounters. Just finding these items in the wild may encourage the party to take a break from the alchemy jug approach.
Let the players try this approach. If they end up relying on it, you can use it for plot hooks. A party that is reliant on one trick will have to get creative when that trick is stolen or rendered ineffective.
It should be noted here that the Replicate Magic Item infusion does require an item of the appropriate type to be infused. For the Alchemy Jug, a non-magical 1 gallon ceramic jug is probably the appropriate item to require. If they aren't carrying around a spare jug, then they aren't able to replicate the Alchemy Jug.
Also, when the Alchemy Jug is replicated, the previously infused jug loses it's magic properties. By allowing artificers in the game, you or your players may take advantage of this for a con. Sell the infused magic item and replicate it in the morning. The previous magic item is now mundane and the party (or conman) profited without loss. Just make sure to add bounties when this ruse is discovered.