When do you need one and how to make one.
Yeast. One of the most amazing and gifted lifeforms on the planet. Used by all in the brewing world to transform that sweet-tasting liquid into the amazing alcoholic beverages we know and love.
Liquid yeasts vs dry packaged yeasts
Most brewers use cultured yeasts provided to them in either dry or liquid forms. There are numerous benefits and drawbacks for each.
Dry packaged yeasts are a great option for brewers, especially those new to brewing. Dry yeasts provide a large number of viable yeasts cells, the packs can be stored for an extended period of time (up to 2 years in the fridge) and can be prepared quickly on brew day. Most brewers use one to two packets (11 – 22 grams) for fermenting 25L of beer, cider or mead.
One of the greatest benefits of dry yeast is its cost; dry yeast is fairly cheap. It is for this reason that it is easier to just buy more yeast rather than making a starter with dry yeast. Additionally, there is some evidence to suggest that making a starter with dry yeast uses up much of the cell’s glycol reserves, making for a sluggish and possibly stuck fermentation.
Dry yeast should also never be sprinkled on top of the wort or must. The high osmotic pressure of the wort can shock yeasts cells before they have a chance to activate. Instead its best to rehydrate your yeast and then add it to the wort.
To prepare dry yeast:
- measure out one cup (237 ml) of warm, boiled water (35ºC – 40ºC) in a sanitised wide-mouthed jar or container.
- Slowly sprinkle the yeast on top. Do not stir the yeast in. Cover the jar loosely with aluminium foil and wait 15 minutes.
- Gently stir the yeast in to suspend it completely.
- Give it about 15 minutes to completely rehydrate. The yeast will form a creamy layer on the bottom of the jar.
- For best results, stir the yeast and pitch within 30 minutes.
Liquid yeasts usually come in a sealed foil package or in a vial. One of the benefits of liquid yeast is the huge variety of different strains on offer, covering practically ever style of beer, cider and mead you’re ever likely to make. Some of the downsides of liquid yeasts include the fact that they have a considerably shorter shelf-life than dry yeast (usually around 6 months) and are more expensive.
The key downside to liquid yeast is their shelf-life – cell viability rapidly drops off over time.For good calculator to work out how much viable yeast you have left in your liquid yeast package try this one.
When Do You Need a Yeast Starter?
Poor viability of an older package of liquid yeast is just one scenario where it can be beneficial to make a starter and increase the number of cells prior to pitching the yeast. Something else that needs to be taken into consideration is pitching rate. Pitching rate, put simply, is the number of yeast cells per millilitre of wort. Different styles of beer have different required pitching rates. For instance low-alcohol beers and many ales require lower pitching rates than high-alcohol or lager-style beers
|Recommended Pitching Rates for Ale Yeast Strains As a Function of Wort Gravity|
|Wort Gravity||Cells per 20 litres||Cells per ml|
|Less than 1.055||60 -120 billion||3 – 6 million|
|1.055 – 1.065||120 – 180 billion||6 – 9 million|
|1.065 – 1.075||180 – 240 billion||9 – 12 million|
|1.075 – 1.085||240 – 300 billion||12 – 15 million|
|1.085 – 1.095||300 – 360 billion||15 – 18 million|
|Greater than 1.095||360 – 420+ billion||18 – 21 million|
Most liquid yeasts will have around 100 billion yeast cells. This equates to a pitch rate of about 4.8 million cells / ml for a 21L batch or 4 million cells / ml for a 25L batch. One package is often enough for most of your usual ales. However, for lagers the pitching rate is much higher.
|Recommended Pitching Rates for Lager Yeast Strains As a Function of Wort Gravity|
|Wort Gravity||Cells per 20 litres||Cells per ml|
|Less than 1.055||120 – 180 billion||6 – 9 million|
|1.055 – 1.065||180 – 240 billion||9 – 12 million|
|1.065 – 1.075||240 – 300 billion||12 – 15 million|
|1.075 – 1.085||300 – 360 billion||15 – 18 million|
|Greater than 1.085||360 – 420+ billion||18 – 21 million|
Not all liquid yeast packages will have the required pitching rate, especially after viability is taken into account, or if you’re making a lager. When this is the case, we need to make a starter.
Making a Yeast Starter
While you could just buy several packets of liquid yeast, this can get expensive. It is easier and much cheaper to make a starter and increase your yeast cells on your own. Making a starter can help you to increase your cell count to the required pitching rate from a single pack of liquid yeast. You can make multiple starters one after another until you reach the right pitch rate. This is called stepping starters, you can find a calculator to work out more detailed multi-step starters here.
But for now, here is a basic starter guide for a single “smack-pack” of liquid yeast:
- Boil 470 ml of water and stir in a 1/2 cup (120 ml) of dry malt extract. This will give you a small amount of wort with a starting gravity of 1.040.
- Boil this for 10 minutes. Put the lid on the pan for the last few minutes, turn off the stove and let it sit to cool.
- Add a quarter teaspoon of yeast nutrient (vitamins, minerals, biotin, and dead yeast cells). This will help the growth of the cells in the starter.
- When the wort is cooled (to between 18ºC and 24ºC), pour all of it including the sediment (the sediment contains lots of useful proteins and lipids) into a sanitised container. The container can either be as lovely and expert as a conical flask or as ghetto and basic as a 2L Coke bottle.
- Take a gravity reading using a hydrometer or a refractometer. As long as the reading is between 1.030 and 1.040 its all good.
- Follow the instructions on the pouch. This might be “smacking” it or bursting a pouch inside. Pouches and vial usually instruct you to bring them to room temperature, with the pouches often swelling to show their viability.
- Sanitise the pouch or vial that contains the yeast. Also sanitise the scissors you will use to cut the pouch. Open
- Pour the contents of the pouch or vial into the starter wort.
- The next step is to aerate the starter mixture. There are a two options to do this:
- A stirrer plate. These are the things you might often associate with laboratories. They use a magnetic “bean” which goes inside the container. This bean is spun using magnetism on a motor from the bottom, creating a vortex and oxygenating the wort. Turn on and leave it on until your starter is ready. This is the most effective way of oxygenating your starter.
- Shaking. Put a lid on the container and shake the hell out of it. This dissolves oxygen into the wort. If you are using a plastic coke bottle or something similar, squeeze the sides to empty the bottle of the excess headspace (and CO2) and suck in fresh air. Put on the lid and shake. Easy! While this is less effective than a stirring plate, it is easy and still has pretty good results. Shake every hour or as often as you can.
- After you shake, seal the lid with either foil, a airlock or half screw the lid on.
- It will take anywhere between 24 and 72 hours for your starter to be ready. You know it will be ready when the gravity hits between 1.004 and 1.008.
- Once your starter is ready, chuck it in the fridge until the yeast forms a thick creamy band at the bottom of the container. If you want, decant the spent wort and pitch the remaining yeast-rich slurry into your beer-to-be. Be sure that the temperature of the starter is within about 6ºC of the wort of your beer-to-be (or cider or anything else).
There you have it. An easy to follow guide of how to make a yeast starter. While you don’t necessarily need a starter for every brew, it doesn’t hurt to make one. While you can over-pitch yeast, being a little bit over doesn’t hurt. If your liquid yeast is getting a bit old, or you suspect it might have been kicked around the back of the home-brew shop by the give-a-shit attitude wielding delivery guys, then try making a starter.
Now that you know how to make one, go forth and let those yeasties multiply!