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When we add yeast nutrient, what are we trying to achieve?

A healthy fermentation. Yeast that gets through the sugars, finishes the job and makes good beer.

Fair enough.

But it's easy to take that a step further and think, well, if a little helps, perhaps a bit more gives me some extra insurance.

That's the bit I want to look at today.

Because what we feed our yeast can affect more than how well it ferments. It can also affect the aroma we get from our hops.

And if you're chasing passionfruit, guava or grapefruit in your beer, that extra food might have a result you weren't expecting.

Let's have a look.

First, when I say yeast nutrient, I'm not talking about one particular ingredient.

Some products supply nitrogen. Others supply vitamins, minerals such as zinc, or a mixture of those things. So two products with “yeast nutrient” on the label can be doing quite different jobs.

Your wort already supplies nutrients as well, largely from the malt.

Today, the part we're interested in is nitrogen.

You'll often hear brewers talk about FAN, Free Amino Nitrogen. It's a useful measure of the amino nitrogen in your wort, although it doesn't tell you everything about yeast nutrition.

Yeast needs nitrogen to grow and build things like proteins and enzymes. But there's more than one place it can get it, and it doesn't use every source equally.

Keep that in mind, because first we need to talk about thiols.

Thiols are aroma compounds that can contribute passionfruit, guava, grapefruit, white grape or blackcurrant character, depending on which compound we're talking about.

And it takes an incredibly small amount for us to smell them.

The catch is that a lot of that aroma potential comes into the brewery in a bound form. Hops and malt contain molecules called thiol precursors.

Think of them as wrapped presents.

The potential is there, but we need to get the wrapping off before we get the aroma.

During fermentation, yeast can take up some of those precursors and use enzymes to break them apart, releasing the aromatic thiol.

So having the precursors in your wort is only part of the job. We also need the yeast to do something with them.

And here's where feeding the yeast gets interesting.

Imagine you've walked into an all-you-can-eat buffet.

Your favourite food is right there, ready to go. You're probably not going to spend much time hunting around for something that's harder to get at.

Yeast has a version of that going on.

When yeast has plenty of its preferred nitrogen sources, whether from the malt or a nitrogen containing nutrient, it can dial down some of the pathways it uses to find and process alternatives. 

That process has a wonderfully catchy name: Nitrogen Catabolite Repression.

You don't need to remember that. Just remember the buffet.

When and if the preferred food starts running low, some of those alternative pathways can become more active. And some of the nitrogen containing molecules the yeast can process also carry bound thiols.

And when yeast processes those molecules they can release aroma thiols along the way.

You see what I’m getting at?
If there’s easy nitrogen sitting there, the yeast can take the easy route and miss some of the molecules carrying our bound thiol aromas. 

Obviously, yeast isn't deciding what to have for lunch. That's a simplified way of explaining how it regulates its metabolism, and different strains respond differently.

But it gives us a reason why more available nitrogen might mean less thiol release.

Some work from Oregon State University funded by Lallemand put that question to the test.

They compared a low FAN wort, a normal all-malt wort and a high FAN wort made with a nitrogen-rich nutrient addition. The high FAN wort got something like six to ten times the label dose. That's a stress test, not a normal addition. 

All three had the same starting gravity. So they were changing the nitrogen supply without simply making a weaker or stronger beer.

And the low FAN beers ended up with more free thiols. In some comparisons, up to three times more of compounds such as 3SH and 4MSP.

Now, if I stopped there, this would sound like a fairly easy brewing tip.

Less nitrogen. More thiols. More tropical beer.

Except that last step didn't follow.

The medium and high FAN beers came across as more tropical, even though they contained fewer thiols.

They also contained more fruity esters from fermentation.

We talk about individual aroma compounds because it helps us understand what's happening. But when you lift a glass to your nose, you don't smell a thiol number.

You smell the beer.

You've got thiols, fruity esters, other hop compounds, and whatever else fermentation has contributed, all arriving together.

Those compounds can complement each other or change how we perceive the overall aroma.

So you can increase one group of compounds without increasing the character you actually wanted.

That's why “more thiols” and “more tropical” aren't interchangeable.

Too much of some thiols can be really bad, you can get those catty, vegetable and sweaty body odour aromas from high concentrations of certain fruity thiol combinations.

It also makes me think about lighter beers.

Take an adjunct lager. If you replace some malt with rice or corn, you're replacing an ingredient that supplies nitrogen with ingredients that supply very little.

You can reduce the nitrogen supply that way.

And if you're brewing a lower-gravity beer with less malt per litre, that can also mean less FAN, depending on the recipe and mash.

Here in Australia, we've got a huge mid-strength market. We're very familiar with a 3.5% beer.

So could the lower nitrogen supply in some of those recipes encourage more thiol release?

That's a reasonable question to ask.

Some brewers report exactly that, smaller beers, less hops but with better or equal aromas to their bigger brothers, we can’t say exactly right now but maybe just maybe this is why.

It doesn't mean every mid strength beer has low FAN, or that 3.5% does something magical to the yeast.

But it gives us something more useful to think about than alcohol percentage alone: what nitrogen is actually available in that wort, and how does the yeast respond to it?

Now, before anyone takes this as a reason to throw their yeast nutrient in the bin.

No.

Yeast still needs adequate nutrition. Too little nitrogen can slow fermentation and cause problems. Getting more aroma out of the hops isn't much of a win if the fermentation struggles.

What I'm questioning is the assumption that an extra spoonful is always helpful.

Start by looking at what your nutrient actually supplies.

If it's mainly vitamins and minerals, reducing it isn't necessarily going to recreate a low FAN wort. If it supplies nitrogen, then it's more directly relevant to what we're talking about.

Use the recommended dose as your starting point, and be careful combining products, especially if both contain zinc.

And if you’re curious about a lower addition, I think it’s worth trying as a controlled comparison. Your grain may already be supplying enough of some nutrients. But adding a bit extra feels like insurance, doesn’t it? The question is whether that extra addition is actually helping your beer. 

A useful way to do that would be two otherwise similar batches: your usual addition in one, a lower addition in the other.

Watch how they ferment. Check where they finish. Then compare the aroma in the glass.

Because that's the result we're interested in.

Most of us aren't measuring FAN at home, so there's no neat instruction here to halve your nutrient dose and expect more passionfruit.

Your wort matters. The product matters. The yeast matters.

For me, the interesting change in thinking is that feeding yeast isn't just about helping it get through the sugars.

We're also influencing what it produces along the way.

Lower FAN can encourage thiol release, but the beer with the highest thiol concentration might still be less tropical than the beer beside it.

So the goal is a healthy fermentation that gives us the flavour we're chasing.

And nitrogen is only one part of that. Temperature and yeast strain also have a big influence on thiol release.

If you've tried different nutrient additions, or noticed something interesting in a lower-gravity hoppy beer, let me know in the comments. I'd like to hear how it fermented as well as how it tasted.

With all the new products hitting the market with thiol release in mind, it's worth remembering that too much thiol is rarely a good thing.

The products can be expensive, and thiols are incredibly fragile, so they can be lost quickly from a simple mistake.

Oxygen and metals like copper chemically destroy them.

They're also volatile, so they can escape into the air.

Some of that happens during fermentation, when CO2 bubbling out can carry aroma away with it.

If you ferment under pressure, there's a simple fix. Lallemand suggest spunding early, after 24 to 72 hours, at a low pressure, so less of that aroma gets blown off with the CO2. 

And some brewers reckon a good chunk of what's left is gone shortly after you pour, so enjoy the beer fresh and get your nose in early.

Most of you are probably leaning towards a NEIPA or hazy style beer, where you should be taking as much care as possible to limit dissolved oxygen and any copper contact. But if you're brewing anything else with thiol products, take that same care. You should be anyway.

If you love your beer, look after it!

Sources and further reading

1. Main research paper
   Wort Nitrogen and Yeast Strain Drive Thiol Release, Flavor Expression, and Fermentation Performance in Beer
   https://doi.org/10.1080/03610470.2025.2530859

2. Lallemand’s Oregon State research summary
   FAN, thiol release and sensory results.
   https://www.lallemandbrewing.com/en/global/resources/whats-new/thiol-research-partnership-with-oregon-state-university/

3. Lallemand’s thiols guide
   Thiol precursors, yeast and nitrogen availability.
   https://www.lallemandbrewing.com/en/africa/biotransformation-resources-center/thiols/

4. Process considerations for biotransformation
   Includes fermentation management and early spunding advice.
   https://www.lallemandbrewing.com/en/canada/biotransformation-resources-center/process-consideration-for-biotransformation/

5. Preserving thiols in homebrewing
   Oxygen control, transfers and packaging.
   https://www.lallemandbrewing.com/en/asia/resources/whats-new/preserving-thiols-in-homebrewing-a-step-by-step-guide/

6. YeastLife O technical data sheet — PDF
   Recommended addition rates for the nutrient used in the study.
   https://connect.lallemandbrewing.com/wp-content/uploads/2021/03/ABV_NUTRIENTS_TDS_YEASTLIFE-O_ENG_DIGITAL.pdf

7. Temperature and yeast strain research
   Lallemand’s summary of further Oregon State research.
   https://www.lallemandbrewing.com/en/canada/resources/whats-new/which-factors-influence-thiol-release-new-osu-thiol-research-published/

Today we’re taking the next step:
Hardness versus alkalinity,
why brewers mix them up,
and how Residual Alkalinity, or RA, predicts mash pH.

This is Part 4 of the brewing water series.
Links to the earlier videos are in the description.

Let’s get into it.

HARDNESS VS ALKALINITY

Hardness and alkalinity get mixed up constantly
because both are reported as CaCO₃.

But they are completely different things.

Hardness comes only from calcium and magnesium.
Doesn’t matter what salts they come from,
if the ions are calcium or magnesium, they count as hardness.

Alkalinity comes almost entirely from bicarbonate.

Two different roles.
Two different behaviours.
Same units purely for convenience.

HARDNESS IN BREWING

Hardness affects mash performance.

Calcium improves enzyme stability, conversion, hot break,
yeast flocculation, and clarity.

Magnesium provides a small nutrient boost for yeast.

Hardness generally helps lower mash pH.
It does not raise it.

WHY CaCO₃ IS USED FOR BOTH

Labs express both hardness and alkalinity “as CaCO₃”
because calcium carbonate makes the maths easy.

Its molecular weight is 100.
Its equivalent weight is 50.
And it reacts cleanly with acids.

It’s simply a unit of convenience.
The chemistry is completely different.

RESIDUAL ALKALINITY, THE MISSING LINK

Here is where hardness and alkalinity finally come together.

Residual Alkalinity, or RA, tells you:

After calcium and magnesium have lowered mash pH,
how much alkalinity is still pushing the pH back up?

High RA means your water tends to raise mash pH.
Low or negative RA means your water lets pH fall easily.

Two waters with the same alkalinity
can behave very differently in the mash
depending on the hardness levels.

RA is the tug of war
between hardness pulling down
and alkalinity pushing up.

It doesn’t give an exact mash pH,
but it tells you which direction your water wants to go.

Understanding RA helps you predict mash pH far better
than alkalinity alone.

BREWER’S QUICK GUIDE

Hardness high and alkalinity low,
great for pale beers.

Hardness low and alkalinity high,
pale beers will fight you, you will need acid or RO dilution.

Both high, as long as you keep them reasonable,
are great for dark beers.

Both low,
like RO water,
build any profile you want.

HOW TO BALANCE HARDNESS AND ALKALINITY

To raise hardness:

Add calcium chloride, calcium sulfate, or magnesium sulfate.
Different salts change flavour balance differently.

To lower hardness:

Use RO dilution.

To balance hardness with alkalinity:

Adjust both separately,
then look at RA to fine-tune mash behaviour.

Brewing software makes this much easier,

but understanding the concepts gives you control. 

Today we’re diving into a topic that confuses brewers more than almost anything in water chemistry: alkalinity.

pH VS ALKALINITY

pH and alkalinity are not the same thing. pH is the ratio of acid to alkaline.

Alkalinity is the amount of alkaline that is present. Two completely different things.

Let me make this clearer with a couple of analogies.

CAR AND CARAVAN ANALOGY

Imagine you are towing a caravan.

The car pulling it is acid. The caravan is alkalinity.

If the caravan is light, even a small car can move it.

That is low alkalinity, and a tiny bit of acid shifts the pH easily.

If the caravan is heavy, the car struggles.

That is high alkalinity, and the pH barely moves even with a fair bit of acid.

That is alkalinity, resistance to lowering pH.

MARBLES ANALOGY

Now imagine marbles.

Red marbles are acid. Blue marbles are alkaline.

One red and one blue marble gives you a neutral balance,

I am using pH 7 here simply as a teaching analogy.

But the alkalinity is tiny, add one more red, and the pH shifts dramatically.

Ten red and ten blue, still neutral, but alkalinity is higher,

add one red and the pH only moves a little.

One hundred red and one hundred blue, still neutral, but alkalinity is huge,

add one red marble and the pH barely moves.

pH is the balance. Alkalinity is the amount.

THE THREE DEFINITIONS OF ALKALINITY

Water treatment people use three definitions.

Number one, Alkalinity is the water’s ability to resist a pH change.

Number two, Alkalinity is the water’s ability to neutralise acid,

in other words, how many bases in the water can mop up hydrogen ions.

In brewing, that is almost all bicarbonate.

Number three, Alkalinity is how much acid it takes to push the water down to pH 4.5.

Below that, alkalinity is gone, and pH falls very quickly.

Your water report’s alkalinity number is based on this pH 4.5 test.

pH 4.5 is the standard endpoint for total alkalinity titration.

We will go deeper into that another time.

WHAT ALKALINITY ACTUALLY MEANS FOR BREWERS

Alkalinity is your water’s ability to resist a drop in pH.

It comes from bicarbonate, carbonate, and a tiny bit of dissolved CO₂.

Here is an important detail, in normal drinking water, pH 7 to 9,

over ninety eight percent of the carbonate system is bicarbonate.

So for brewers, alkalinity basically is bicarbonate.

Bicarbonate is the primary buffering system in brewing water.

WHY ALKALINITY MATTERS

High alkalinity raises mash pH, it can make pale beers harsh, dull, or grainy.

Low alkalinity lets mash pH fall easily, great for pale beers,

but it can fall too low in dark beers.

Very low alkalinity, around 0 to 30 ppm, can make beer taste thin or watery.

Moderate to high alkalinity, around 100 to 200 ppm,

helps buffer the acidity of roasted malts in stouts and porters,

and it prevents acrid, burnt flavours.

Pale beers want low alkalinity.

Dark beers want moderate to high alkalinity.

 HOW TO ADJUST ALKALINITY

To lower alkalinity

Use lactic acid or phosphoric acid, acidulated malt,

or dilute with RO or distilled water.

Prefer lactic or phosphoric,

they are predictable, repeatable, and easy to calculate.

Why not rely heavily on acidulated malt?

Because its acidity varies between maltsters,

large amounts can add lactic flavour,

and it makes mash pH correction slow and imprecise.

Dilution

Dilution works well when you do not need a huge correction.

If your alkalinity is 100 ppm and you want around 50,

a simple one to one mix of tap water and RO or distilled water

will get you close.

De- alkalisation by boiling

You can also remove alkalinity by boiling. Bring the water to a rolling boil.

You may add a small sprinkle of chalk to speed things up,

but boiling alone will remove some alkalinity.

Boiling drives off CO₂, and once the CO₂ is gone, 

the water cannot hold as much bicarbonate.

Calcium and bicarbonate will crash out as chalky solids.

Let it cool, let it settle, and pour off the clear water from the top.

Done properly, this usually leaves you with around 60 to 90 ppm alkalinity.

To raise alkalinity

Use baking soda, it is the easiest and most predictable method.

You can use chalk, but it barely dissolves unless the water is carbonated,

so it is difficult to use correctly.

Slaked lime works too, but it is tricky, it's easy to over correct and can be corrosive.

Most brewers should stick to baking soda.

So in summary:

pH is the balance.

Alkalinity is resistance to lowering that balance.

And bicarbonate is the superstar behind it all.

In the next video, we will look at how alkalinity interacts with hardness,

and how Residual Alkalinity, or RA, predicts mash pH even better.

Every brewer seems to know that one guy who  says, 

“Mate, you ONLY need this magic number,” or 

“This ONE mineral is all that matters.” 

 Yeah… nah, not even close. 

 That’s marketing hype mixed with wishful thinking. 

Water chemistry is a team sport, not a solo act, and pH 

is one of the Most Valuable Players. 

From your mash, to the boil, into the fermenter, and all 

the way to that final pint, pH is quietly influencing 

everything, like a backstage manager that never sleeps. 

And sure, you might fluke a good beer without paying 

attention to it, but if you want to dial things in, fix 

problems, and make beer that tastes intentionally good 

instead of accidentally good, pH is your new best mate. 

This is Part 2 of my brewing water series, so if you 

missed Part 1, it’s worth watching. It’ll make some of the 

terms in this video make a lot more sense. And, like 

always, I tuck a bit of bonus science at the end for the 

curious minds who enjoy a nerdy nightcap. If you 

skipped that in Part 1, or haven’t watched it at all, there’s 

a link in the description. 

 Fun Fact - Oxygen means Acid Maker 

Alright, before we start throwing numbers around like 

we’re filing tax returns, it helps to understand why pH 

does what it does and what’s actually going on behind 

the scenes. 

 So let’s kick off with the basics. 

What does pH mean?

pH p=Power H=Hydrogen 

pH stands for the “Potential of Hydrogen” 

 More accurately, the "p" is a mathematical notation that 

stands for the negative logarithm (base 10) of the 

concentration or activity of hydrogen ions ([H⁺]) in a 

solution. Remember at School, yep one of those buttons 

on your calculator Log Sin Cos.  

 You might be used to hearing “acid and alkaline” but 

since we’ll be talking about alkalinity in another video, 

it’s less confusing to use the word "base" or “basic”. So 

you have acids and bases. 

 In simple terms, pH is a scale that tells us how acidic or 

basic water is. It’s based on the concentration of 

hydrogen ions present, acids gain hydrogen ions  and 

create hydronium and bases are created by losing 

hydrogen ions and creating hydroxide but because 

those numbers get incredibly small, we use a logarithmic 

scale to make it easier to work with. 

 A logarithmic scale simply means each 1 step change in 

pH represents a tenfold change in acidity. For example, 

something with a pH of 5 is ten times more acidic than 

something with a pH of 6. 

 If we look at the pH range from 0 to 14, each step is a 

tenfold change, which means the entire range spans a 

factor of 100 trillion. That’s an almost unimaginable 

difference. If pH 0 were represented by a single 1mm 

grain of sand, then pH 14 would be 100 trillion grains, 

enough to fill 40 Olympic swimming pools or build a 

small beach. If pH 0 was 1 second, then pH 14 would be 

over 3 million years. This is why the pH scale uses 

logarithms, to compress a truly enormous range into a 

simple number. 

Why does pH matter in brewing

pH is crucial because it affects almost every stage of brewing: 

1. Mash Efficiency 

Enzymes like amylase convert starches to sugars 

best in a slightly acidic range, around 5.2 to 5.6. 

Outside this range, enzyme activity drops, reducing 

sugar extraction, efficiency and ultimately affecting 

alcohol content. 

2. Flavour Development 

pH affects the taste of the final beer: 

 Lower pH can make beer taste sharp or tart. 

 Higher pH can lead to dull or soapy flavors. 

pH also influences hop utilization, too high or too 

low can reduce bitterness extraction. 

We will dive deep into pH and beer flavours in a 

future video. 

3. Yeast Health & Fermentation 

Yeast prefers a slightly acidic environment. Correct 

pH helps yeast ferment efficiently and reduces the 

risk of off-flavors or stalled fermentation. 

4. Microbial Stability 

A lower pH helps inhibit unwanted bacteria, 

improving the beer’s shelf life and safety. 

5. Clarity & Stability 

pH affects protein precipitation and polyphenol 

interactions, which influence clarity and haze formation. 

How to Measure pH

1. pH Test Paper or Indicator Sticks 

These strips change colour depending on the 

acidity or alkalinity of your solution. You dip the strip 

into your liquid and compare it to a colour chart. 

Each colour corresponds to a different pH. Though I 

am yet to find any with high accuracy. And with dark 

beers that can change the colour of the strip, 

accuracy is near impossible. 

2. pH Meters 

A probe is dipped into the wort or beer, giving a 

precise digital reading. Many, if not all serious 

brewers who care about their beer use pH meters. 

They are used through the whole process from 

mash to fermenter. A detailed test equipment video 

will be later in this series. A quick tip for those 

already using them, calibrate whenever you use 

them and make sure the calibration fluid is at room 

temperature around 20c or  68F and the same with 

the wort sample,  doesn't matter if it has ATC 

Automatic temperature correction or not, to get 

accurate readings it’s what you have to do.  

Tip 

To some people this might sound odd, but in brewing, as 

long as you’re starting with potable water, water that’s 

safe to drink, the actual pH of your tap water isn’t a big 

deal, it doesn’t matter. In most places it falls somewhere 

between 6.5 and 8.5 anyway. Once you add grain, the 

mash naturally contains buffers that pull the pH into a 

range that's easily tweakable when needed, so the 

starting water pH rarely affects anything by itself. 

Buffers, that brings us to Alkalinty, that's for the next 

video and it is hugely important.  

pH tells us the ratio of acid to base, but it doesn’t tell us 

how much total acid or base is in the water. That’s 

where alkalinity comes in.  

 In the next video I’ll show exactly why alkalinity matters, 

and why water with high alkalinity is much harder to shift 

in pH than water with low alkalinity.