About brewing yeast

The magic of brewing yeast

Yeast is the powerhouse behind the brewing process.

To help yeast do its job, you must make sure it is viable and you are pitching enough yeast cells to adequately ferment your beer.

Unfortunately the usual five gram packet of brewing yeast supplied with your tin of concentrated homebrew is probably:

  • Old.

  • Tired.

  • Too small to do the job.

  • Generic.

If your yeast is not up to the job of fermenting your beer, other micro-organisms (ie bacteria and wild yeast) will happily step into the void. The results will be ordinary.

For these reasons I suggest buying a packet of premium brewing yeast for a few extra dollars and reading on carefully.

Never use baking yeast. It makes great bread but terrible beer.

What does brewing yeast do?

In short yeast eats sugars. The bi-product of this is carbon dioxide and alcohol. This makes beer bubbly and enjoyable.

The longer version is more complicated but if you get your head around the basic concept, you’ll be fine.

Brewing Yeasts: Ale (warm) or lager (cold)

There are dozens of strains of brewing yeast available to the modern homebrewer, but all can be classified as either ale or lager.


Ale yeast is where I suggest you start. An ale yeast is one that works at higher temperatures (generally 64-75°F/ 18-24°C) and ferments in the top part of your wort. The results are generally earthy and wholesome.

Styles of beer in the ale camp are APAs, IPAs, stouts, bitters, milds and porters.

Wheat beers with their distinct and delicious phenolic banana and clove notes are a subset of ale.

Primary fermentation time is much quicker (four to six days), compared to lagers.


Lager yeasts are the sophisticated cousins. They work at lower temperatures (generally 48-60°F/9-15°C), operate at the bottom of the wort and are crisp, refreshing and clean. Think pilsners and lagers.

Fermentation time is longer (up to two weeks). The beer also benefits from a short warmer period in the last two days of fermentation known as a diacetyl rest.

There are some exceptions to these rules but more on this another time. For now think along the dichotomy of ales or lagers.

Whether you use one or the other depends on the type of beer you are trying to make and your ambient brewing temperature.

Dried vs liquid brewing yeasts

Brewing yeasts are sold either dry or liquid. Given the great quality of dried yeast in the market and their ease of use, I encourage you to leave liquid yeasts for later.

I use dried yeast exclusively with great results at home and in competitions.

Beer needs healthy yeast

To use dried yeast correctly you must use an adequate amount and rehydrate before pitching.

If you use 11 grams of healthy yeast for a six gallon (23 L) batch, you are pitching enough for it to do its job.

As mentioned earlier, the five gram packet taped to the top of your homebrew tin is not enough cell mass to cleanly ferment your beer.

Rehydrate for homebrew

Before pitching, you need to rehydrate your yeast with water that has been boiled and cooled.

Adding dried yeast direct to your wort will destroy the yeast wall as the sugary solution moves into the cell.

Up to 50% of viable cells can be destroyed, limiting your yeast’s performance.

To rehydrate you follow a few simple steps:

  • Boil your kettle and let cool. For ales, cool to 86°F (30°C). For lager yeast aim for 77°F (23°C).

  • Clean and sanitize a packet of dried yeast, drinking glass, thermometer and scissors.

  • Pour a cup of the cooled kettle water into the glass.

  • Recheck the temperature.

  • Wearing your sanitized brewing gloves, cut the top off the yeast package.

  • Sprinkle on the water surface and cover with sanitized plastic wrap.

  • Leave for 15 minutes and swirl around to mix in.

  • Leave for a further 15 minutes. You will see the yeast has developed a creamy head.

  • Pitch your yeast into your wort.

If your brewing yeast does not produce the above results it may be old and unviable. Not good for great beer.

If you have a spare 11 gram packet use this instead. As a last resort, use the original yeast packet that came with the kit.

A word on fermenting temperature

Make sure your fermenter is fitted with a stick on thermometer so you can monitor your wort’s temperature.

Too cold

If wort temperature falls below the operating range of the yeast, it will become sluggish and leave the job undone.

This can be disastrous – residual bottled sugars will continue to ferment. This creates excess carbonation, explosions and household tension! Again not good for brewing.

The best way to monitor fermentation is with a hydrometer.

Too hot

If your beer ferments above the yeast’s operating range, it will produce off flavors, unpleasant solvent-like alcohols and headaches.

You really need to brew in the yeast’s preferred range for great beer.

Find out more about temperature control.


Homebrewing With Kits—The Beginner’s Guide

To help you master homebrewing with kits, I’ve put together a guide based on my experiences over nearly two decades of homebrewing.

This is the information I wish I had when I first started. I hope it helps you make awesome homebrew.

Download your copy today.

Homebrewing Basics Series