The answer is yes! This is a great way to produce more beer volume from a brewhouse of a fixed size and is commonly used by commercial brewers around the globe. The economics of this are simple: Two single-batch fermenters cost 2 units of currency, one double-batch fermenter costs about 1.3 units of currency, and one quadruple-batch fermenter costs about 1.7 units of currency. The commercial economics become even more pronounced when the cost of cleaning, labor, utilities, instrumentation, and automation are considered. Multi-batch fermenters have a multitude of real advantages. There are a few general tips to consider when putting more than one batch into a single fermentation vessel.
Multi-Batch Tip #1:
Most breweries fermenting multiple batches of wort in a single fermenter fill the fermenter within about 18 hours because periods longer than this can result in an interruption in the way yeast grow and transform wort to beer. Without getting in the weeds of this topic, you will be a happy and successful multi-batch brewer if your first brew fills into the fermenter towards the end of day one and the second brew fills into the fermenter before noon on the following day. If you brew on the weekend, this means doing a late afternoon/early evening brew on Saturday and a morning brew on Sunday (or Friday evening and Saturday morning). Your first brew may just be beginning to ferment when your second brew is added. Brewing both brews in the same day is preferred, but this can seem more like work than having fun!
Multi-Batch Tip #2:
Add all of the yeast pitch, enough for the combined volume, to the first brew. As you become more experienced with this method you can reduce the yeast pitch rate because there is yeast growth in between initial pitching and the second batch of wort flowing into the fermenter, but beginning conservatively is a good plan. Ideally the two brews are produced in the shortest timeframe possible and the yeast population is likely in the lag phase (still no growth — reproduction has not yet commenced) when the second batch of wort is added to the fermenter.
Multi-Batch Tip #3:
Commercial breweries aerate in-line between the wort cooler and the fermenter. A two-brew fermentation is usually aerated on both fills when the two brews fill into the fermenter before yeast growth begins. Many breweries will skip aeration after yeast growth takes off. You can aerate your fermenter twice if the two batches are filled in quick succession, but if the two batches take longer than ~8 hours to produce consider skipping the second aeration. Why aerate twice? If the second batch comes in without aeration, the oxygen content of the wort is diluted and may cause fermentation issues. If you are using dried yeast, aeration is not a concern because dried yeast does just fine in non-aerated wort. This is another topic for another day!
Multi-Batch Tip #4:
Limit your multi-batch brewing to two batches per fermenter. Things become a bit more complex when fermenters contain more than two batches. Some brewers add yeast with alternating wort fills and also alternate how wort is aerated. This can all be done at home, but you are looking to solve a practical problem that is easily addressed without adding too much complexity.
Multi-Batch Tip #5:
Another method that works very well at home is to simply ferment your two brews as independent batches and blend the two batches together after primary fermentation is complete. If you normally rack your beer into a secondary, this would be an ideal time to conduct the blend. If you use a single-vessel process, you can rack one of the batches into the other provided your fermenter is large enough.