Many brewers are daunted by the idea of yeast starters, but with a few basic tips and a bit of practice, you won’t look back. Over the course of the next few months, I will cover the basics of yeast, from propagation, to its health.
The most important lesson I have learnt while brewing, and I cannot stress it enough, is keeping your yeast happy. Happy yeast is happy beer. It is almost like yeast is the afterthought after a long, tiring day of brewing, and few of us realise the importance of choosing the correct yeast, and knowing how to keep it happy. Many of us are not pitching the correct amount of yeast into our wort. Either we are on a budget, or we are just guesstimating, and don’t really know where to start. Once I discovered the importance of pitching the correct amount of yeast, I have never looked back. I achieved a noticeable improvement in the resulting beer: it fermented faster, aging time was massively reduced (you’ll get to drink it so much faster ), and there was a clear reduction in unwanted yeast by-products, such as acetaldehyde (green apples). In addition to all these benefits, correct pitching rates also help to prevent potential contamination by wild-yeast or bacteria that may have snuck in (such as Pediococcus and Lactobacillus). By starting with a high number of yeast cells, you are reducing the likelihood of any potential foreign microbes from replicating sufficiently to outcompete the brewing
yeast and become a problem. (However, please note, if your cleaning process is not adequate, no amount of yeast will prevent a contaminated beer).
First off, you need to remember that yeast is a living organism, and, like us, it needs nutrients and minerals to stay fit, strong and happy. This comes in the form of sugars, nitrogen, amino acids and fatty acids (majority of which comes from the malt, but also from specific yeast nutrients such as the
Servomyces Yeast Nutrient). In addition, yeast, like us, does not perform well under stress. Yeast can be stressed by numerous things, such as high sugar concentrations, low pitch rates, incorrect reproduction/fermentation temperatures, pH etc. Ensuring you have created the best environment for
the yeast, you will massively improve the quality of the resulting beer.
For the purposes of this blog, I am going to concentrate on pitching rates.
Mr Malty (http://www.mrmalty.com/calc/calc.html) is an invaluable tool to help you calculate the correct pitching rates for your brew. After playing with the calculator, you will soon see that the suggested pitching levels stated on most dehydrated sachets of brewing yeast are actually too low (11.5g per 20-30 liters). To use an example, you need 10g of dry yeast for 20 liters of 1.050 gravity wort. Baring in mind, this is using yeast that was produced on the 3 March 2015 (maximum viability).
However, most dry yeast we purchase are already a few months old. So remember to take that into consideration, as you will then need to pitch more yeast. For a 6 month old sachet, you would then need 12g of yeast.
Lagers require a higher pitching rate than ales (the reasons will be covered in a future blog). For a 20 liter lager of 1.050 starting gravity, you need 21g of dehydrated yeast (of the same viability as the ale as previous). This is over double the amount of yeast that is required for an ale. (Remember, stronger beers also require a higher pitching rate).
And for a 6 month old sachet, you will need 23g for your 20 liter lager.
Under pitching causes the yeast to reproduce a lot more than a higher pitch would, before all the resources are consumed. This results in a beer that has more yeast character (esters etc.), while those beers that are pitched higher tend to have a cleaner fermentation with less yeast character.
Belgian-style and wheat beers (eg. Weiss) add a whole new aspect to your approach to yeast however, and defy everything I have just told you. What makes these beers unique, is their fruitiness (eg. banana- called esters) and their spiciness (clove-like- called phenols). What gives these beers their
characteristics, is playing with the fermentation temperatures, their starting gravity, and pitching rate and achieving the correct balance. Higher fermentation temperatures results in more esters produced (more fruity/banana like aromas), while more phenols are produced at lower fermentation
temperatures (spice/clove-like aromas). Some Belgian breweries start at a lower fermentation temperature for phenol production, and then allow the fermentation temperature to slowly increase, thereby increasing the production of esters. Each brewery has their own balance of esters/phenols for
their beer. Just a side note, don’t ever decrease the fermentation temperature once fermentation has begun, this causes the yeast to go into survival mode, and drop out or go to sleep (stuck fermentation) (yeast does not like to be wrangled). You may need to re-pitch with healthy yeast. (As a home-brewer, it is advised to stick with the suggested fermentation temperature for your specific yeast). In addition, a reduction in your aeration will increase the production of esters, while increased aeration will reduce esters. Pitching rates also alter ester production. Some brewers like to under-pitch to increase fermentation characteristics in their beer. It is all about achieving a balance between all these parameters to reach your goal profile.
After saying all this, there is also such a thing as too much yeast. Extreme over pitching causes the yeast to consume the nutrients too quickly, causing starvation, the build-up of unused metabolic products and yeast death, all of which will add unwanted characteristics to your finished beer.
Of course, pitch rate is just the beginning of the yeast story. Yeast health, available nutrients, pH and fermentation temperature are all contributing factors in achieving great beer, but realising yeast is a living organism that needs a little TLC (tender, loving care) is the first giant step in the right direction to achieving great beer. Till next time, keep on beering! Megan
More about the Author, Megan Gemmell:
When I am not working as a microbiologist, I am brewing and studying beer. Being the geek scientist that I am, brewing yeast has become one of my main interests. After many years of brewing on my home-made system, squeezed into the laundry, I have taken the plunge and started Clockwork Brewhouse, and I’m loving it.
Visit Clockwork Brewhouse http://www.clockworkbrewhouse.co.za/