This one is a toss up. For a first venture into mead, unsure if the first batches are going to work out or not, it makes sense and cost effectiveness to make small batches, using one gallon carboys. These are pretty easy to find -- juice containers or jug wine bottles make nice one gallon carboys.
On the other hand, that first mead, especially with good aging, may be so fantastic that you'll want to have a five gallon carboy batch, so you can continue to enjoy it. One gallon batches can go quickly!
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