With an ever growing range of yeasts available in the UK, more and more home brewers are experimenting with them but they don’t always realise that they need to be handled with proper care.
Most home brew yeast either comes in two forms. Dried or liquid. Depending on which type you opt to use will determine the preparation required prior to pitching.
When using any yeast you will need to determine the correct pitch rates for your beer. This will vary depending on volume, starting gravity and fermentation temperature. The more sugar there is to ferment, either by volume or starting gravity, then the more yeast that will be required for a healthy fermentation. Temperature will also increase the need for higher volumes of yeast but this is only really relevant if you are brewing a lager style demanding a low fermentation temperature and therefore require a larger pitch.
Pitching the correct amount of healthy yeast is crucial for good fermentation. This will normally be indicated by a short lag time (the time it takes for visible fermentation to start) and expected attenuation (fermenting to the expected final gravity). The wort is most susceptible to contamination during the lag stage so the shorter the better. Under pitching also puts extra strain on the yeast causing unwanted flavours and aromas.
We would recommend using a pitching calculator to determine the amount of yeast required.
Due to the drying process, dried yeasts are pretty stable and will contain almost the same amount of viable yeast cells per gram even when they are several months old. This generally considered to be around 20 Billion cells per gram of yeast. We would always recommend rehydrating before use. Simply boil 100ml of water and cool to 35c in a container. Add the yeast and mix to a paste, cover and leave for 15 mins. Then stir and pitch. Obviously ensure all equipment is clean and sterile.
As they are fresh, Liquid yeast packs will deteriorate fairly quickly. Use the manufacture date in the calculator to determine how many viable cells are left. Wyeast, White Labs and Yeast bay saccharomyces strains will start with 100 Billion cells per pack. Gigayeast start with around 200 Billion cells per pack. If the pack is a few weeks old, which they usually are, you will need to make a yeast starter to increase the cell counts prior to pitching. Brett and Bacteria will have generally have lower starting volumes.
Making a yeast starter may sound daunting but it’s pretty simple. Firstly determine the size of starter required using the calculator.
For example, assume we want to ferment 20 litres of ale with a starting gravity of 1.054. This requires 200 billion yeast cells at pitching.
If we are using a single pack of whitelabs liquid yeast manufactured 3 weeks ago this will mean that it is now 82.3% viable. This gives us approximately 82.3 Billion yeast cells.
If we make up a 1.5L starter, using the shaking method of stirring then this will give us 205 billion cells which is what we require.
To make the starter first we need to make some wort using light dried malt extract. You can again use the calculator to determine the amount of malt extract required, always using a 1.037 starting gravity. In our example we require 132g of extract made up to 1.5 litres with water. Boil for 10 mins then cool to around 22c. Transfer to a sterilised vessel with is bigger than the total volume so there is plenty of headspace to allow air in. As we are making yeast not beer we want plenty of oxygen throughout the process as this will help maximise the yeast growth. Place a loose lid over the top to prevent dirt from entering but allowing oxygen to ingress.
You can make life easier by preparing the starter in a Erlenmeyer flask. The major advantage of this is that you can boil the wort and cool in the flask, which avoids having to sterilise a separate container. If not then any container will work.
Now the starter needs rousing and the method used dictates the “method of aeration” selected in drop down in the calculator. Although you can opt for none, this will decrease the number of cells grown and therefore increase the size of the starter. Shaking method means that every time you past the starter you give is a good rouse or shake. In reality 5 or 6 times per day will suffice.
The most efficient method is using a stir plate. This works by having a magnetic bar placed in the vessel which is then constantly stirred throughout the process which dramatically increases the number of cells created.
Whichever method you decide, you need to ferment the starter for around 48 hrs at around 22c then leave overnight to settle out. If you put in a fridge, this will help the yeast settle out just remember to allow to come back up to room temp before pitching. The starter can be kept in the fridge for a few days if needed.
Once you are ready to pitch, simply pour off as much of the liquid as possible leaving enough to get all the yeast back into liquid form so you can pour into your fermenter.
If you need a very high number of cells you can step up the starter in stages. Perform each stage as above, pitching the yeast into the new stage after each fermentation.
Other than good hygiene, good fermentation will have a greater effect on the finished beer than pretty much any other factor and therefore requires the correct attention.
For further info check our video on our youtube channel which will go through making a yeast starter. Please also feel to contact us via email@example.com of via our live chat where we will always be happy to help.