During the early days in my brewing adventures a fellow homebrewer asked how much yeast I was using. Like most beginners, I was pitching yeast directly from the packaging into the fermentor. While I was making some good beer this way, l was informed that in most cases – especially with high gravity beers – I was not pitching enough yeast to get the best possible fermentation. In fact, I had noticed that some of my beers had not attenuated to the desired final gravity, and wondered if this was the reason. So I began to look into ways of increasing the amount of yeast cells used during fermentation to see how that affected the finished product.
Let’s go back to the basics. The amount of viable cells in a package of liquid yeast is going to depend on not only the manufacturer, but the freshness of your yeast. After liquid yeast has been packaged, the percentage of viable cells can decrease around 20% per month. The more yeast cells you lose due to age, the less likely you’ll get a good fermentation.
Underpitching yeast – meaning you haven’t used enough – can potentially lead to off flavors in the finished product due to competition with wild yeast and/or bacteria present thanks to a slow start to fermentation. Underpitching can also cause high levels of diacetyl and/or acetaldehyde. Dry yeast on the other hand has a higher density of cells per gram and is cheaper than liquid yeast. The downside to dry yeast is a lack of variety, and there is no guarantee of purity because of the drying process. Whatever type of yeast you choose, you’ll want to make sure you’re using enough.
The size of the batch of the beer being produced, the gravity of the wort being fermented, and the type of beer being made – lagers require more yeast cells – all play a role in the amount of yeast cells needed to properly ferment the beer. Most brewing software programs such as Beer Smith have a yeast pitching rate calculator built in. If you’re not using brewing software, Mr. Malty’s Pitching Rate Calculator™ is a great free online resource to determine how much yeast you need to pitch for proper fermentation. The Mr. Malty website was created by homebrewer-turned-pro Jamil Zainasheff who co-authored Yeast: The Practical Guide to Beer Fermentation with Chris White of San Diego’s own White Labs.
With liquid yeast, the amount of vials or packs can be staggering if you’re brewing large batches of high gravity beer. A great way to keep the cost down is to grow up more yeast cells yourself by creating a yeast starter. Making a yeast starter is easy, and it will confirm the viability of the yeast you are using. Yeast starters only require some water and malt extract – either dry or liquid, but dry is easier to deal with. Use the yeast pitching calculator to determine the size of the starter needed. A ratio of ½ cup of dried malt extract (DME) to 1 pint of water – or one gram of DME to 10 ml of water – will create a starter with a specific gravity around 1.040. Mix the DME with the water and boil for at least 10 minutes. Feel free to also add yeast nutrient as well. Cool the wort to a temperature within the range that the yeast ferments, and pitch the yeast. Make sure that all equipment post-boil is cleaned and sanitized.
An Erlenmeyer flask is a great vessel for making a starter since you can boil liquid inside of it, cool the wort to pitching temperature, and ferment the starter without having to transfer any wort between vessels. If you don’t have an Erlenmeyer flask, you can clean and sanitize a glass or stainless steel growler to add cooled wort to.
Using a stir plate will also increase the cell count as the starter is constantly stirring in oxygen for the yeast to grow, while getting rid of CO2. The increased gas exchange of a stir plate can produce nearly twice the amount of cells of a non-stirred starter. If you don’t have a stir plate, just swirl the growler of yeast as often as you can. With dry yeast, making a starter is not beneficial – just follow the manufacturer’s instructions of re-hydration or direct pitching.
You will also get more yeast growth the warmer the starter is – with diminishing returns once you exceed 90˚F – but you will want to pitch the whole starter of yeast as close to fermentation temperature as possible. Big drops in temperature can shock and stress the yeast to the point of ruining the benefit of making a starter in the first place. If the starter is too warm, let it completely ferment out, cool to fermentation temperature, and then pitch the yeast after decanting any liquid on top of the yeast, which should be settled on the bottom.
RESOURCES
Books:
How To Brew – John Palmer
The Complete Joy of Home Brewing – Charlie Papazian
Podcasts:
The Brewing Network’s Brew Strong and The Jamil Show – thebrewingnetwork.com
BeerSmith Home Brewing Blog – beersmith.com/blog
Articles:
Brew With Fermentis Tips & Tricks – brewwithfermentis.com
Proper Yeast Pitching Rates on Mr. Malty – mrmalty.com/pitching.php
YouTube videos:
Homebrew 101: Making a Yeast Starter by Beer Geek Nation
Making A Yeast Starter by Northern Brewer TV