itle

Brewing with yeast

brewing with yeast


The year was 1836 when Baron Charles Cagniard de la Tour, a French engineer and physicist proved that yeast were living organisms, totally changing the paradigm that yeast were not chemical substances.

De La Tour was the first to postulate that yeast was the cause of alcohol and CO2 production.

And ever since then, yeast has been king when it comes to beer.

In this post we cover a range of brewing matters that involve yeast. First up is the basic question of:

What is yeast?


Yeast is a single cell microorganism and it's actually technically a fungi.

While there are many varieties of yeast, the ones brewers typically use, ale and lager yeasts are members of the family Saccharymyces Cerevisiae.

If you don't use yeast when making beer, you do not get fermentation occurring.

No yeast, no booze.

That said, you don't just 'add yeast' to your beer like you would adding flour to a cake batter. Like most elements of making a good beer, there are all kinds of things that need to go right with the yeast for a beer to be a good drop. 

What is the difference between an ale and lager yeast?


Ales are known as “top fermenting” due to the yeast layer that forms at the top of the fermenter. Lagers yeasts are called “bottom fermenting” as, you guessed it, they ferment at the bottom. 

Ale yeasts will best ferment in the range of 10-25 centigrade and produce beers high in esters and often lower in attenuation. These are both distinctive and desired characteristic of ales.  

Lagers ferment in the colder range of range from 7-15C and produce a cleaner beer with lower esters.

Woah Nelly, it's getting hot in here!


Yeast is, as De La Tour proved, a living thing so it needs to be treated right. And the first thing we should talk about is correct brewing temperature.
That’s why pitching your yeast is more than simply adding it to your beer – it needs to be done at the correct time in the brew so that it can activate properly.

The short version is if you pitch your yeast when your brew is too hot (say you’ve just boiled it), you will kill the yeast with the heat and fermentation will not occur.

For this reason, only add the yeast to the fermenter when you have filled it to the 23 litre mark with a lot of cold water. If you are aiming to get the yeast going at the suggested range, let it warm in the sun a bit. You can take it's temperature using a thermometer and you are good to do.

How to re-hydrate your yeast before you pitch it


A handy method that many earnest brewers follow is to hydrate the dry yeast in water before pitching. The reasoning behind this is that it gives the yeast a good chance to get started properly before it comes into contact with the sugars.
Rehydrating yeast in a glass

The theory at play is that theconcentration of sugars in the wort can mean it is difficult for the yeast to absorb water into its membranes so that they can begin to activate / metabolize and thus commence the fermentation process

Based on that, I imagine that if you have made a high gravity wort that's full of sugar and other fermentables like DME for the yeast to eat, hydration is a good step to take.

In my experience I’ve never had the yeast fail with a simple beer kit but if you are keen to cut the potential problem out, feel free to re-hydrate your yeast. 

The professional way to this this by boiling some water and letting it cool. You can then add your yeast packet (or two!) to the water and let it begin to absorb – you shouldn’t do this too far apart from when it is time to pitch the yeast. You can even add some sugar if you are super keen.

Cover and leave for about 15 minutes and then inspect. It should have begun to smell like you are making bread and 'bubbled' a bit (see the above picture). If so, it’s ready to be pitched.

Once you've added the yeast to the wort, there will likely be some left in the glass - I have a 'waste not want not' kind of view so I add some water to the glass, give it a swirl and add it to the yeast as well.

What is attenuation?


In the context of beer brewing, attenuation is the percentage that measures the conversion of sugars into alcohol and carbon dioxide by the fermentation process.

A well attenuated beer will have a drier characteristic and have a greater competent of alcohol than a less attenuated beer.

Brewers measure attenuation because it is an indicator of yeast health and because specific attenuation levels are important for certain styles of beer. For example, if a beer does not attenuate to the expected level in fermentation will have more residual sugar and will thus be sweeter and heavier-bodied than planned.

The brewer would then investigate that the yeast was up to the performance level required or that it was used under correct brewing practices (such as appropriate temperature).

The typical values for attenuation percentages are:

Low: 72 percent and lower 
Medium: 73 to 77 percent 
High: 78 percent and upwards

How do I work out my attenuation rate?


You'll need to take readings with your hydrometer to determine your rate of attenuation. You then use this formula:

(original gravity - current gravity) / (original gravity - 1)

This will work out the 'apparent attenuation'. Remember to use your BEDMAS.

-

So the selection considerations of your yeast should reflect on what kind of beer you wish to brew. If you are making an ale, you'll want to choose a yeast that produces a lower rate of attenuation.

Brewers regularly use the following yeasts with ales:

For a lager yeast which will cause a higher rate of attenuation, you could try:

Saccharomyces cerevisiae beer yeast cells

Using old yeast can affect the performance of the yeast


Facts are facts, you need enough yeast to get all the sugars and other fermentables in the wort. 

If the yeast in your packet or vial are only half healthy, then you'll need to find that extra 50 percent from somewhere as the amount of yeast in the packet is measured out so the standard 23 liter brew can be properly fermented.

So basically, if you're using old , tired yeast, you might need to compensate for that by using two packets. Which is in effect adding an extra cost to your brew.

Many modern’s brewing recipes take the view that you are pitching fresh yeast and even further, that the yeast has been prepared in nutrient rich yeast starter.

If you 'under pitch' your viable yeast then it's quite likely your yeast will be under pressure to perform and you will get a low rate of attentuation - which this will alter the the intended characteristics of the beer you are trying to make.

So, the lesson here, as for most things in life (like hops), fresh is best!

Can I use baking yeast to ferment beer?


Many craft brewers would probably shudder violently at the suggestion of using a yeast that's normally used to make bread.

The truth is, you can baking yeast for brewing, as both yeasts (beer and baking) are different strains of the same species, saccharomyces cerevisiae.

You'd being doing yourself a service to ask 'what is the difference between baker's yeast and brewer's yeast?'

The difference between the two kinds of yeasts lies in the history of their cultivation.

Each has been grown for the the attributes they bring to the final product. In the case of beer yeast, the popular strains have been cultivated for hundreds of years to hone their specific attributes being the beer flavor produced, attenuation, and consistency.

Beer yeast will flocculate better than baker's yeast. When brewers yeast nears the end of fermentation, single cells aggregate into clumps of thousands of cells (flocculation), and drop to the bottom of the fermentor, leaving clear beer behind. Baker's yeast is not as flocculant.

Beer yeast that floccuates well will contribute to having clear beer.

A good way to look at the difference is that brewer's yeast was bred to produce more alcohol and less carbon dioxide while baker's yeast was bred to make more CO2 and less alcohol.

So be warned - using a baking yeast in place of a brewing yeast is like driving a Ford and expecting to drive like a Ferrari!

Using a yeast starter to increase the viability of the yeast


For complete fermentation to occur, the yeast cells need to begin to reproduce at an optimum rate. Temperature plays a vital role in the rate at which this can occur. The choice of beer style can run counter to allowing this. We're basically taking lagers here. 

If you are brewing a lager, you'll know from above that it best ferments at a temperature range lower than an ale at 7 - 15 centigrade. That cooler temperature can impede the performance of the yeast. 

While you could simply add even more yeast, that again costs money, so enter the use of a yeast starter. The idea is to develop a ready culture of yeast that can be used to carry out the fermentation of wort into clean beer. A properly prepared yeast sampler will have enough cells in it to do the required job, meaning the cold temperature should not impede the yeast.

So how do you make a yeast starter You follow the sage advice of John Palmer. At the very least, if you are using dry yeast, you should add it to a class of warm water and a little bit of sugar about an hour before you are ready to pitch it into your yeast.


When yeast might need a helping hand at the end of fermentation


As a round of a difficult fermentation draws to an end (temperature variance, over saturated wort), you may need to rouse the yeast convince it to finish the fermentation. If your fermentation is not quite at the desired final gravity and it seems to have stalled then there's a simple trick to do.

Stir the beer few times gently. This will cause the yeast that may the fallen to the bottom, to re-integrate with the wort again and find some new sugars to eat. This trick works best when fermentation is occurring at the higher end of the the yeast's operating tolerance.

If you're brewing environment is too cold, you may need to warm the wort and then stir.

Be careful not to aerate your beer or add nutrients if your fermentation is nearly done.

What is the shelf life of yeast?


Dry packet yeast, if stored properly, have a fairly long shelf life. I've seen punter say it will last upwards of a year or even two when stored in the fridge.

Dry yeast certainly loses viability over time so if you are using an older yeast, beer in mind that you might need to account for that by pitching an extra amount.

This is why many brewers would recommend that you do not use the yeast packet that comes with a beer kit as you don't know how long it has been sitting around. That said, I've been using kit yeasts for years and never had a problem. That said (II), when I have used Safale 05 it felt like the batch started fermenting furiously fast from the get go.

Liquid yeast is another story. Results may vary - many liquid yeasts come with the recommendation that they be used within three months date of their first shipping from the manufacturer but they can keep pretty well for 6 months in the fridge.

The better stored the yeast is, the longer it will remain viable

It is very common to use prepare a liquid yeast by way of a yeast starter. Even packets and vials where there are very few viable cells can be revived and multiplied with a well made yeast starter.

The loose rule of thumb then is that dry yeast has a shelf life of 2 years and liquid yeast 6 but you need to try and factor in the decay rate of the yeast.

If in doubt, make test the yeast with some water and sugar or make a starter.

Can I pitch multiple yeast strains?


Yes, you can mix the strains of yeast. You will get a mix of the properties of each yeast which will have an impact on the flavour of the beer. Where large commercial brewers are basically making lagers like Heineken, they are not focused on getting flavor combinations from yeast.

 Craft brewers, who by nature are 'taste explorers', readily seek out new flavors by mixing up their yeast or combinations.

Their quest for flavorful ales, wheat beers, Belgian beers, and strong beers has led them to mix things up.

The mixed yeasts do not compete over each other, they each simply go about fermenting. Given yeast imparts is flavour into the beer in the first 36 hours, each yeast should be added at the same time.

If you are trying to fix an issue of low attenuation by adding more yeast, then by all means you can add more yeast as little flavour will added to the brew at that late stage.

Yeast tolerance to alcohol



You might think it odd given yeast makes alcohol that you have to account for the alcohol produced.
A yeast strain can tolerate only so much of it before it stops working. Over the centuries yeasts have been studied and cultivated and beaten into submission so much so that there a plenty of strains that can handle high solutions of alcohol.

Such yeasts are desired to that they are able to fully ferment what's offered in the wort. There's simply no reason to let a beer be half fermented is there? So chosing a yeast that can handle the ABV of the beer you intend to brew is a no brainer.

Many yeasts do fine in the 3 - 5 per cent range, many Belgian yeasts get found out at 8 percent. A few hardy nuggets can go beyond 10.

 When going beyond 8 per cent, beers need a bit of extra love. Extra nutrients may be required, a high concentration of pitching yeast than normal should be used, the yeast should rousing, and warmer temperatures will help get the yeast ticking over.

If you are keen on brewing very high ABV beer, you'll need to appreciate that such beers may taste quite sweet or they can even become unpalatable.

No comments:

Post a Comment