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Fermentation

Fermentation Process

This is simply the process of turning sugar into alcohol using "Yeast". Once you have prepared a wort that you are ready to ferment, you just add yeast. After 12 - 24 hours the yeast will have multiplied enough to start turning the sugars into alcohol. You should see a thick foamy head develop on top of your beer which indicates fermentation is well under way. The first few days should show fairly vigorous activity but after day 4 it will usually begin to slow down. After 7 -10 days the fermentation should be complete. This can be tested by measuring the specific gravity (see below) or simply looking to see if the bubbles have stopped rising. If you have fitted an airlock (not essential) you will be able to see that the airlock stops bubbling when fermentation ceases.


Once fermentation is complete, you are ready for kegging/bottling. Depending on how you will store / serve your beer, will depend on how you will need to clear the beer, see the Kegging page for further information on this. Basically, if you are bottling or using a conventional plastic barrel you can transfer the beer while it is still cloudy and then allow the beer to clear / condition. However, the corny/sankey kegs will need the beer cleared before kegging.

Fermentation Vessels

Primary / Secondary

Buckets, dustbins, carboys, wine fermenters etc. are all fine to use as fermenting vessels. As long as they are new and clean. You do not necessarily need a vessel with an airlock as many brewers still ferment in open vessels. For home brewing it is best to use something with some kind of lid to stop the cast falling in or bogey fingered children investigating.

Some books and beer kit instructions advise you to move your beer to a secondary fermentation vessel after the initial primary fermentation has completed (around 7 days). This is said to have the advantage of moving the beer away from the spent yeast, producing a cleaner tasting beer. However, this does increase the risk of infection and if you are using quality yeasts you are best to leave this step out. The Fermentation process also creates something called "Diacetyl", which gives the beer an strange flavour, see the yeast section below for more information on this..

I usually ferment in a closed wine fermenter with the airlock removed for the first week and then fit an airlock for another 2-3 weeks while it clears.

Airlocks

Not strictly necessary but if you are going to clear your beer before Kegging / bottling then you will need to use an airlock after primary fermentation has finished. Fermentation can be extremely violent in the first few days so fitting a small wine airlock is a bit pointless. Once primary fermentation is complete a standard wine airlock will work just fine.

Yeast

Dried Yeast

Dried yeast have been given a bad name by the cheap versions which are bundled with Beer Kits. This is no longer the case as production techniques for dried yeasts have become extremely advanced over recent years resulting in some excellent dried yeasts becoming available. I have even heard reports of commercial brewers using dried yeasts.

A commonly used quality yeast is Safale S-04.This yeast ferments fast, clears quickly and leaves virtually no after taste. Some of the cheap yeasts supplied with beer kits leave some awful tastes and smells behind in the finished beer. There are many other varieties of quality dried yeast available but what you choose depends on the type of beer you are brewing. Take a look at the Fermentis website and also BrewUk where you can read user reviews to investigate this further.

Liquid Yeast

These are very expensive but also seem to be popular and well reviewed. It is also possible to select a yeast that is closest to your beer type from a vast range available, which is not something you can do with dried yeasts. It is worth noting that yeast contributes quite heavily to the overall flavour of a beer, so if you are trying to achieve a taste that is similar to your favourite commercial beer, you will need to use a liquid yeast strain. For this reason the liquid yeasts are superior to the dried ones but that does not mean you will get a better beer, just different flavours and character.

If you brew regularly then you can recycle the yeast across several brews, which reduces the cost but I do not brew frequently enough to take advantage of this. Given the excellent results that I have been getting with Safale S-04, which is relatively cheap, I have used this in a lot of my beers quite successfully.

Starters

Most books state that making a yeast starter is an essential step of improving your beer. Over the years I have found that more problems are created than solved when making up a starter. On a few occasions, my starter has failed to ferment once added to the wort. This may be due to temperature variations or incorrect sugar levels in the starter but yeast can be temperamental once it has started to ferment (as it has in a starter). Using a good dried yeast, I have never failed to get my wort fermenting well and it tastes just fine. If you are new to brewing I would recommend using dried yeast without a starter.

The liquid yeasts seem to have some very specific instructions when it comes to brews with a high OG or of larger brew lengths. In these cases a starter is essential. Liquid yeasts also have a much shorter shelf life, so once they are near the best before date, a starter is recommended.

To make a starter you will need some DME and of course your choice of yeast. You need to keep the specific gravity of the starter between 1030 and 1040 as this is best for yeast growth. You also need to keep the starter well aerated as this is also essential for good yeast growth. It will take around 48 hours for the starter to have developed to the point that it is ready for pitching, so you need to plan ahead of your brew day.


For a 5 gallon brew the typical starter size would be 1L. To make a starter of this size use 1L of water and 1 cup of light DME, which will get you somewhere between the 1030 and 1040 SG required.

Ensure that all equipment is sanitised then put 1L of water in a saucepan. Bring the pan to boil and add your DME, stirring well, then continue to boil for around 10 minutes. You then need to cool your starter wort to the correct yeast pitching temperature (around 20C). Pitch your yeast and give it a really good shake to ensure adequate aeration. You can either cover your vessel with foil OR add an airlock and then keep in a warm place to grow. Keep agitating the yeast during the next 48 hours as this promotes healthy yeast growth. When you are ready to pitch the starter, decant off most of the liquid and then mix the yeast back into solution with the remainder and pitch. You should see signs of active fermentation within a few hours.

Some brewers will also use a stir plate to help grow their starter. This is not essential but does assist in growing as much yeast as possible.


Harvesting Yeast

This should not be done if you have used a dried yeast as you will get better results from a fresh packet. If you are using liquid yeasts then you can re-pitch the yeast into several brews. The best way to re-use yeast is to collect the yeast cake from the bottom of your fermenter. there are quite a few people that recommend washing the yeast but I have not found this to be necessary. You will have quite a lot of yeast, so sterilise some bottles and split this into 4 or 5 containers. These should then be stored immediately in the fridge and will keep for some time. In the first few days you should keep releasing the pressure build up in the yeast container as this is not good for the yeast. If you are re-pitching the yeast within 4 weeks then it is probably OK to just warm to room temperature and pitch. If the yeast has been in the fridge for any longer then it will be best to make a starter.

Diacetyl

Diacetyl is created by the yeast as a "by product" of the fermentation process. To achieve a clean tasting beer, it is preferable to minimise the amount of Diacetyl in the finished product. Once the yeast has converted all the available sugars into alcohol, it will start to feed on the Diacetyl and effectively clean up after itself. This is why it is important to leave the beer on the yeast for a few days after the fermentation has completed, racking to a secondary vessel too early can adversely effect the quality of the final beer.


Temperature

In order to get the best performance from your yeast and ensure that you produce a quality beer, temperature is the most important factor in fermentation. Not only do you need to keep the temperature within certain tolerance levels, you also need to maintain a constant temperature. Yeast is a living organism and does not respond well to sudden changes in temperate. The more constant the fermentation temperature the better your beer will be, so you may want to invest in some form of temperature controller. See the equipment page

The temperature that is used for fermentation is usually between 18 and 22 degrees Celsius but this will depend on the type of yeast being used, so read the instructions carefully. If your temperature is too low, you will experience a very slow fermentation and introduce the risk infections getting into the beer. If the temperature is too high, the fermentation will be too vigorous and produce esters and "off" flavours. Having said all this, in my younger years, I have produced some very acceptable beers while taking very little care over temperature.

Stuck Fermentation

There are some rare occasions when a fermentation can become "Stuck". There can be many causes for this and it can just occur randomly so be prepared in case it happens to your pride and joy.

Causes Of Stuck Fermentation

These are the main causes of a stuck fermentation.

There are probably other causes as yeast is a living ingredient but these are the main ones for us to consider.

Solving a "Stuck" Ferment

Start by checking and adjusting the temperature of the wort, usually 18-20C is best. Then gently rouse the wort as the yeast may just need waking up. Leave to ferment again for a couple of days and then check the SG readings. If these are still high then you may have to add some more yeast but this should be a last resort. If none of this works ensure your wort is safely under airlock and just leave it for a few weeks. Sometime fermentation can just be very slow. If the final beer still has a high SG but tastes OK then drink it but if it has off tastes then you have no option but to throw it out.

Clearing / Fining Beer

Once fermentation has finished you will need to consider how you want to clear your beer. A lot of home brewers simply Keg/bottle the beer straight after fermentation and then allow to clear naturally. After the secondary fermentation has taken place (3-4) days the Keg/ bottles are moved to a cooler location and left to clear. This can take 4-6 weeks before the beer is ready to drink.

Most breweries favour the clearing of beer prior to Kegging/Bottling using a clearing agent. This has a few advantage :

The chemicals commonly used to fine/clear beer are:

Both the products above have their own set of instructions. I have found that it is best to rack the beer out of the primary and add finings in a secondary vessel. The secondary should then be left under airlock for about a week after which, the beer will be clear.

Specific Gravity

The specific gravity of the wort tells us how much sugar is in solution. This is very useful information and is monitored during the fermentation process. When the wort has finished fermenting most of the sugars will have been turned to alcohol by the yeast. The Specific Gravity reading can therefore be used to confirm that fermentation is complete.

Original Gravity (OG)

The original gravity of a beer will depend on the recipe and the mash efficiency. Typically a stock beer of around 4.8% ABV would have an OG of somewhere in the region of 1.050. The more sugars in the wort the higher the OG reading will be. Although the OG reading usually gives you an idea of how strong a beer will be you also have to consider the OG reading to work out the alcohol content.

Final Gravity (FG)

At typical beer would finish fermenting with a reading of say 1.012 but this can be higher or lower depending on the type of beer and the amount of un-fermentable sugars generated by the recipe you have used. The usual guide to see if fermentation has finished is if the SG reading remains static for 3 days but be careful as fermentation can become "stuck" in certain situations.

Calculations

Using OG and FG readings, you can calculate the amount of alcohol in the beer using some simple formula. There are many tools for this on the internet so I have rarely used a calculator to do this. The Beer Engine software calculates OG / FG and ABV for you so I suggest using this.

If you own a refractometer then you will need to convert Brix readings into SG. The OG readings are fairly simply but once the wort has started fermenting you need to adjust the Brix readings for the alcohol content. There are many formulas for doing this and everyone seems to disagree on which formula is best. There is a tool in beer engine but I have found that this does not give me good results. The spreadsheet published by MoreBeer does seem to follow my hydrometer quite closely so I prefer this calculation, which can be downloaded from the link below.



MoreBeer Refractometer Calculation Spreadsheet