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After Denny's article in the spring issue of Zymurgy, I'm anxious to experiment and split batches for experimentation with yeast pitching rates, strains, fermentation temps, and adjuncts.

I had previously done this by doing a high-gravity mash, spitting the wort into two batches, diluting to session levels pre-boil, then changing hop additions.

What are some good containers to use for 1 gallon mini-batches? I have one one-gallon glass jug (likely from a nasty jug wine or something) that I used to use for starters. I also have about 3 extra 5-gallon carboys that I picked up when I thought I would do a lot of bulk aging.

Two questions: 1.) Is extra headspace in a fermenter bad? I could theoretically just use these 5-gallon carboys if not 2.) What are some other suitable containers that people have had luck with in finding inexpensively and readily available small fermentation vessels?

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up vote 2 down vote accepted

My concern with 1 gallon in a 5 gallon carboy is isn't chances of oxidization, since the CO2 produced will displace the air, but the microbial load from all that additional air.

After using a good sanitizer like Starsan or Iodophor the fermentor is close to microbe free and the largest source of contaminants is then the air itself in the fermentor.

With 5 times less yeast, and many times more headspace than normal, you may want to be sure to hit recommended pitching rates, ideally by pitching from an actively fermenting starter, or rehydrated dried yeast to reduce lag times and ensure the yeast come out on top.

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For the first question: It sounds like you're planning on doing a primary fermentation in the carboys. In that case, extra headspace is perfectly fine. Fermentation will produce CO2 to fill up that space and protect your beer from any oxygen coming in, and it will also leave some room for the krausen to take up. One gallon in a 5 gallon carboy might be a little excessive, but I think you'll be fine.

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If the calculations on this thread are correct, fermenting a 5% ABV beer will generate about 20 volumes of CO2. So a 1 gallon batch would produce 20 gallons of CO2—plenty to purge the headspace of a 5 gallon carboy.

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Not a full gallon, but the dollar store has 3 liter PET bottles for a dollar each (dump the soda pop). You can ferment and also bottle in them!

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