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Variables and Variability

Variables and Variability

By Greig McGill

While the title might sound like Jane Austen’s forgotten romance novel set against the backdrop of the steamy science community, I assure you this article is about brewing! Specifically, about how to consider and adjust some of the myriad variables that go into producing your bouncing baby beer. Just what do you need to worry about, and how much? Yep, this is all about process and choice.

The sheer number of variables involved in brewing can be overwhelming, so it’s not surprising many brewers just keep doing what they’ve always done. There’s nothing really wrong with that - it’s your hobby, nobody should tell you how to do it. That said, for those looking to use the principle of least effort/cost for most reward, there are some variables involved in brewing that can be well worth a tweak, as the potential results can range from noticeable to drastic! I won’t be going into the specifics of how to adjust each variable, as there’s plenty of excellent information out there on the web. My intent is to provide a platform for focusing your choices of what to tweak, and provide a starting point for your own research.

A quick note before I continue; if any of you are devotees of Marshall Schott’s excellent Brülosophy website, you may note that his exBEERiments often suggest that many of these variables aren’t as significant as I am stating here. Remember that his methodology and focus is on figuring out what changing a single variable does to the final flavour of a beer, as perceived by “an average drinker”. I have met Marshall, and have a ton of respect for his work with  Brülosophy, but in both my home brewing and professional brewing, I have drawn many different conclusions, and these are what I’ll be sharing here. Of course, you are always free, and encouraged, to make up your own minds!

Water Chemistry and pH

While there’s been significant devotion to water chemistry in recent times, much of that focus has been on flavour in the finished beer. For example, manipulating sulfate:chloride ratio in order to change the perception of hop crispness or rounded mouthfeel in different styles of IPA. While this is reasonably solid from a sensory and scientific point of view, the more important focus of this variable to me is yeast health and impact on fermentation. It’s common these days for people to “just add gypsum” to their IPAs and call water treatment done, without measuring the effect on pH, and thus on fermentation performance. It is well worth taking the time to understand water chemistry and pH in order to balance and tweak your water/mash profiles and thus achieve better, faster, healthier fermentations, and thus better beer.
Pay more attention when: You’ve been struggling with good fermentation performance, or attenuation isn’t where it should be. Also when you want to harvest and re-pitch yeast at maximum health.
Pay less attention when: Fermentation is consistent and your beers taste great.
Tweak when: You want to experiment with hop presence and mouthfeel in your beers.

Fermentation Temperature

Think of temperature as just another stressor on yeast. All yeast strains have their “preferred” temperature range, and to go outside those ranges means you are placing stress on the yeast. Whether that stressor has a negative effect or not is in the mouth of the taster! For example, I love fermenting my English style ales in the higher end of their range, ramping up even higher than their tolerance right at the end of fermentation. I find this maximises ester production and minimises VDK production to ensure a fruity beer without any detectable diacetyl (buttery) presence. Because the stress on the yeast is right at the end, when the yeast would otherwise be “banking” nutrients and compounds to strengthen it for dormancy, there is a negative effect on repitching and so it may pay to top-crop during active ferment if you plan to re-pitch yeast used like this.
Pay more attention when: You’ve had fermentation-related off flavours, or you’re not getting the expected ester profile from your chosen yeast.
Pay less attention when: You have healthy fermentations, producing the flavours you expect.
Tweak when: You’re feeling experimental, and want to give a tried-and-true beer a little something extra.

Pre-fermentation Oxygenation

Oxygen provides the energy the yeast needs for the hard work of reproduction and fermentation. Not enough, and fermentations can be sluggish, taking a long time to kick off, and producing many off-flavours. Too much, and you can get excessive VDK production, and more energy devoted to reproduction than fermentation, leading to reduced alcohol production. Luckily, achieving “too much” is very difficult at homebrew scales!
Pay more attention when: Fermentation doesn’t seem to complete fully, and your beer contains lots of “stressed yeast” flavours like the green-apple notes of acetaldehyde, or when you want to ferment a much higher gravity beer than usual.
Pay less attention when: Never! Oxygen is always important to fermentation, so make sure you’re at least doing something simple like shaking your fermenter for a good amount of time to get a basic level of oxygen after your boil, which drives off oxygen.
Tweak when: You feel like fermentation performance could be a little better, especially in bigger beers.


Dimethyl Sulfide (DMS) is that boiling-vegetable or cooked corn smell. It’s commonly perceived in lagers, because lightly kilned pilsner malt has more of the precursor compounds that form DMS. The main methods of reducing this compound are vigorous boiling, rapid post-boil chilling, and length of boil. Common wisdom is to have a good rolling boil, good steam extraction so the DMS-forming compounds don’t just condense and fall back into the kettle, and to maintain the boil for 90 minutes “to be sure”. In practice, this will depend on the type of kettle you have, the efficiency of extraction, and even the variety of barley and the maltster who produced your grain. It’s one of those variables you can only really tweak with the assistance of someone who is very sensitive to DMS, but it can be worth doing that if you’re finding your lagers (or XPAs, or anything using a lot of very pale malt) are coming out a little “corny”.

Pay more attention when: Your beers are coming out with high levels of DMS.
Pay less attention when: Your beers have no perceptible DMS, or have it at a level you’re happy with.
Tweak when: You want to achieve the classic profile of a beer that actually features a certain level of DMS, or you’d like to eliminate it completely from your beer.


How you carbonate your beer can have a huge effect on the taste and mouthfeel of the final product. Too little carbonation and your beer can seem flabby, and aromas can be lower than expected. Too much, and the beer can seem thin, acidic, and “washed out”. The correct level of carbonation is different not just for every style of beer, but for each individual beer. It’s well worth spending time tweaking this variable, as even professional brewers often miss the mark on this, and when you hit the “sweet spot”, it can really lift a beer to the next level of deliciousness.

Pay more attention when: Your beers seem flabby and heavy, sitting lifelessly on the tongue, or have poor mouthfeel - either too full or too light and spritzy. Aromas don’t pop the way they should.
Pay less attention when: All the beer flavours are in balance, and the mouthfeel is exactly what you’d expect from your beer.
Tweak when: You think your beers are never quite what they should be, but you’re confident that all your other brewing processes are good, and you can’t put a finger on what could be wrong.

As I mentioned in the introduction, there are many more variables that can have an impact on your brewing process. As an experiment, next time you brew, note down every single step of your process and anything during that process that you could do differently, even slightly. Ask yourself what the result would be if you tweaked that thing one way or another. Sometimes it’s good to revisit things we’ve always done a certain way and ask ourselves honestly if it could be done better, but the question should always be asked - “to what end?”

The more you nail down your process to a list of known variables, and have those variables set the way you want them to be, the more consistent your beers will be - or to put it another way, the more variability will be reduced!