Recently, I was party to a discussion on what the ideal boil volume is for partial mash homebrewers. As with almost any topic, a proportion of opinions seem to break down into two disparate “parties” comprised of hardliners, while the rest of the population fall somewhere in between. While this may seem esoteric, I do think that homebrewers should consider their options before settling on hard and fast volumes especially when they embark on the journey of perfecting (or at the very least improving) a recipe. I thought I’d weigh in on the issue…

Small boil volumes

Advocates for small boil volumes, either the smallest possible or significantly smaller than your end batch volume (typically 5 gallons), point to a number of benefits:

  • easier temperature control*
  • less chance of a boil over
  • shorter brew time
  • shorter time to bring wort to a boil and to chill it
  • smaller volumes of water for cleaning and cooling

It should be noted that many beginning homebrewers fall into this category simply out of necessity; they may not yet have access to dedicated and purpose built brew kettles (instead relying on 2-3 gallon pots that are commonly found in everyday pots and pans cooking sets), or perhaps they don’t have access to immersion coolers, sufficiently large coolers, or heavy duty sinks to enable a successful cold crashing (not to mention the immense amount of ice the last two can require).

Large boil volumes

These individuals point at several alternative benefits that go along with larger boil volumes:

  • easier temperature control* (yes I did type this above as well)
  • lower solute/solvent ratio - its easier to dissolve material
  • enables more grains to be used (in relation to LME or DME)
  • less top-off water needs to be used when racking wort to fermenter
  • better hop flavor/aroma realization

My own analysis

So much of homebrewing relies on proper aseptic technique. Everything post-boil needs to be thoroughly cleaned and rinsed followed by sanitization with bleach, Star San, or another cleaning product. Improper cleaning or any other activity that may result in contamination can ruin hours of brewing and days, weeks, or months of fermentation. In light of this, I think that its quite clear that using the largest (feasible) boil volume is the proper way to go. Yes it will take longer to bring your mash to temp or to a boil; Yes it will take longer to cool it down; Yes it will increase your overall brew time. What does one gain by investing more time? A decreased chance of contamination due to bacteria in your top-off water.

When culturing microbes, there’s a reason that we don’t dilute growth media after its been autoclaved, I don’t know why homebrewing would be any different.

*Addendum: on temperature control

There are valid reasons why both camps claim that easier temperature control is obtained with thier preferred method and, funny enough, its for the same reason: thermal mass. Smaller boil volumes are easier to add heat to to bring temperatures up, while larger boil volumes possess higher thermal mass and lose heat more slowly to the ambient environment. For this point the benefit of one approach over the other really comes down to the space, equipment, and burner/stove used by each individual homebrewer. For this reason I consider this point a wash.