Greetings Beer Lovers!
Tonight i started and completed Phase 1 of prep work for Brew Day on 10/31/09, I made sterile wort (a term we brewers use for unfermented beer) for my yeast starters. This operation is usually undertaken 3-5 days before brewing using a well established process that i have used before, but it is a little scary. Before I talk about the process i used I will give a short primer on yeast starters and why we, as brewers use them.
Yeast that is packaged for use for baking or brewing is dormant. Yeasts are a pretty "smart" fungus. They will eat sugars until they sense that their food supply is running out. Once they sense the supply is dwindling, they will stop reproducing, stop the fermentation process; eating sugar and excreting alcohol, CO2, and other compounds, and go dormant. After the yeast go dormant, they can either be kept in a slurry with distilled water, or kiln dried.
Anyone who has done any baking involving yeast, like bread, for example, knows that if you use dried yeast it must be "proofed". This can be done in several ways, depending on what the recipe calls for. Usually the yeast is added to a little warm water and sugar, allowed to rehydrate and become active. This method can also be used with dried beer yeast strains as well. Yeast strains that are chosen to be dried, are usually very robust in order to survive the drying process.
These dried yeast strains can usually just be rehydrated and pitched directly into the wort, especially in lower gravity ale type beers brewed at warm temperatures (60 degrees to 90 degrees) Low gravity beers have a low percentage of dissolved fermentable sugars, to yield low percentages of alcohol and ales are brewed using top fermenting yeast that work at higher temperatures.
This is all well and good, but the variety of dried yeast strains is very limited. There are about 8-10 dried beer yeast strains, and while they have been used by both homebrewers and professional brewers alike, there are many, many yeasts strains from around the world that are not robust enough to be dried, and come in liquid slurry form. The liquid yeasts are where the fun starts for the homebrewer, but they sometimes involve a little extra work, prior to brew day, and that's where the yeast starters come in.
Homebrewers are inventive little buggers. We see equipment and procedures used in large scale breweries, and we try to adapt those to are small scale home breweries. It's like any other hobby, i suppose ya start small and eventually it's a monster, much like this Blog Post! Anyway, when it comes to yeast, large scale breweries employ several methods for getting their yeast into the wort. Companies like White Labs, which serves homebrewers and professionals alike, can provide micro and macro breweries pitchable amounts of liquid yeast, that is amounts that can be directly added to the wort with no further propagation or starters needed. They can provide enough pitchable yeast for wort amounts from 1 barrel (33 gallons) to 200 barrels (6,600 gallons). Micro and Macro breweries can buy a new package of slurry for every batch they make, which is expensive, but guarantees a good quality yeast with no contamination or mutation. Some breweries will harvest yeast from beer while it is actively fermenting and put it in a propagation tank and then pitch it into a batch of beer.
Homebrewers have a few options when it comes to liquid yeast brands. Liquid yeasts offer nearly 80 different varieties of yeast strains which have been harvested, propagated, and perfected from around the world. Some of the worlds most famous beers owe a great debt to the resident yeasts in their local area. Each regional yeast lends its own special attributes to the beer, which home and craft brewers used to make magic!
The two biggest Bbrands that Homebrewers and wine makers use are White Labs and Wyeast. Brewers have their preferences between these two companies. Both provide excellent products, they just come in different packages.
White Labs packages their yeast in small viles in slurry form that they say are ready and viable enough to be directly pitched into a 5 gallon batch, provided they survive shipping in a hot truck.
Wyeast packs their yeast in a foil pack in slurry with a small packet of nutrients and sugar inside the packet. These packs are called "smack packs", because about 12 hours before it's time to pitch, you smack the packet, bursting the inner packet. In about 12 hours they yeast come out of dormancy, reproduce, do a little mini-fermentation and the pack swells. The yeast are proofed and ready to go!
Myself, I prefer White Labs yeast. I have used both, and have had the smack packs fail, and then have to scramble to find yeast on brew day.(there are only a couple of homebrew shops in town and they are far away from me). White Labs says that their viles are ready to go on their own to ferment 5 gallons of beer with no problem. I have done this on low gravity beers and had great success, although the lag (time it takes for yeast to absorb oxygen, start reproducing, and then start fermentation) was a little long, and the longer the lag, the greater chance any wild yeast or bacteria can take over and ruin the beer. To prevent this, a starter can be made, to allow the yeast to grow, become strong, and increase their numbers to be better able to start their fermentation cycle. This is a good thing, and where Phase 1 begins!
The usual process of making a yeast starter for the home brewer starts with boiling water in a pyrex erlenmeyer flask. the size of the flask can range from 500 ml to 4000 ml. I generally use a 2000 ml flask. Anyway, the process after the water is boiling is to add a measured amount of dried malt extract, watch it boil over :) and then let it boil for about 30 minutes. Then, the scary part is, you take this boiling flask and place it in an ice bath to cool down. It goes against every natural instinct to place 220 degree glass into freezing cold water. Even though i know pyrex is designed just for this sort of thing, i cringe everytime i do it. i wear long heavy rubber coated nylon gloves and get ready to run. I figure there has to be a better way, and i think i found it!
Tonight i put 4000 ml of water in a large pot and brought it to a boil. I then started adding dried malt extract and yeast nutrients into the water, had a minor boil over :) and then boiled for 30 minutes. I then prepared 10 pint sized mason jars and got the pressure cooker ready. I then poured the wort into the jars and placed them into the cooker. I processed the jars at 15 psi for 30 minutes. Now I have 10 pints of sterile wort!
When it comes time to make the starters, all i have to do is pour my sterile wort into my two flasks, add my 4 yeast strains, 2 to each flask, and a little nutrients, and let the yeasts propagate! No scary temperature shock, and the wort is STERILE. Usually when using the older method, the starter can be contaminated as it rapidly cools as a vacuum is created (remember the science class trick when ya crushed a can by temperature difference) and can pull in nasty wild yeasts and bacteria.
So that's about it for this post, I know it was long, but i hope i shared my (limited) knowledge of yeast propagation. Many books have been written on this subject, and i could write much much more about the process (i think i may be a lil obsessed lol). i'm excited about this new method of making starters and i hope it will be a success!
Until Next Time,
Gregg, The Yeast Master