On bottling day after having bottled up the very first batch of my 1960's Era Ballantine IPA recipe, one that I had spent a very considerable amount of time researching before creating the recipe and brewing it, I decided to wash the East Coast Yeast ECY10 - Old Newark Ale™ yeast that was at the bottom of the fermentor and store it for later use when making a starter to pitch into my next batch of beer. After cold crashing the washed yeast for five days at 36F the yeast cells flocculated out of suspension and formed a thick cream colored yeast cake on the bottom of the jar. Using a turkey baster I carefully sucked the top layer of the yeast cake into the baster and squirted the yeast into a dozen liquid yeast vials for storage.
|East Coast Yeast ECY10 - Old Newark Ale™|
|One Gallon Of Washed Yeast Slurry|
|Vials Of ECY-10 Estimated 50 Billion Cell Count Each|
|Excess Yeast Slurry At Left Washed Yeast Vials At Right|
|1.040 Starter Wort With Yeast Nutrient And Crumbled Hops|
|Cold Crashing The Boiling Wort To Pitching Temperature|
|Phases Of A Typical Starter Taken 12 Hours Apart|
When making a yeast starter it's critical to formulate, as precisely as possible, the recommended inoculation rate of viable yeast cells for 2000ml of 1.040 starter wort. I use a very simple formula where my inoculation rate starts out as close to 100 billions cells as possible and I expect that number to increase to between 220-240 billion cells once the starters finished.
|Pitching Rate Calculator|
|Cold Crashing Starters At Day 1, Day 2 And Day 3|
|White Labs WLP820 - Oktoberfest/Märzen Lager Yeast™|
At the end of the day all I wanted was the yeast I had no intentions of pitching a gallon of nasty tasting starter wort into my five gallon batch of beer and ruin the taste of it. Placing the starter flasks in the refrigerator at 36F for 3 days did the trick. The starters were very cloudy after coming off the stirplates but began to clear by the end of the first day and had completely cleared by the third day in the refrigerator. Pouring off, or decanting, the starter wort from the flasks and leaving just enough to swirl the yeast cake into solution from the bottom of the flasks and the yeast was now ready to pitch.
|Oxygenated Wort Prior To Pitching Yeast Is The Best|
Now during the primary fermentation, or anaerobic, phase the yeast rewire their pathways and start converting the sugars in the fermenting beer into Co2 and alcohol. By reducing the length of time in the aerobic phase the excessive build up of flavor precursors are also reduced and the primary fermentation that follows can easily convert those precursors before going dormant at the end of the fermentation.
The Four Phases Of Fermentation
Phase 1 begins as soon as you pitch your yeast and is referred to as the lag phase, which we brewers want to keep as short as possible. The yeast are using up the sugars and oxygen in the wort to load up their food reserves, they won't ferment anything until they've been well fed. Stressing the yeast out with too high temperatures or too low numbers of viable cells will prolong the lag phase and the fermentation will take longer to complete while increasing the amounts and types of off flavors like diacetyl that may or may not ever condition out.
Phase 2 starts as soon as the lag phase ends because now the yeast have enough energy stored up to start multiplying, this is referred to as the growth phase. This is where you begin to see a bit of foam floating at the surface the wort from the production of Co2 and the pH and oxygen levels of the wort will start dropping. If you've pitched enough healthy yeast at the right temperatures into well aerated wort the lag time should have been 6-12 hours and the yeast are now full of energy and off to a very healthy start.
Phase 3 begins as soon as the growth phase is done and is triggered by a lack of oxygen in the wort, this is known as the fermentation phase. This is the phase where the production of Co2, alcohol and your beer's flavor is at it's peak and the wort temperature rises 3-5F higher than the ambient air outside the fermentor. The yeast will stay in suspension, so they come in contact with as many sugars as possible, over the next 3-7 days before they run out of sugars to eat and flocculate out to the bottom of the fermentor. Higher temperatures during this phase will produce more esters or fruity flavors and aromas, like the banana flavors in a hefeweizen. It's interesting to note that another cause of ester production is wort that hasn't been aerated enough.
Phase 4 is the final phase of the fermentation process and it's referred to as the sedimentation phase where the yeast begin consuming and converting any remaining flavor precursors in the wort like diacetyl that will produce off flavors in your beer. During this phase the yeast cells are preparing themselves to go dormant and storing up energy reserves for their deep sleep, even though this is where most of us flush them down the drain. I'd like to point out that the amount of cleanup work left for the yeast to do is dependent on how well we treated, or mistreated, our yeast during the first 3 fermentation phases.
During the sedimentation phase I raise the temperature of my fermentors 3-5F and hold it there for at least 3 days before bottling or kegging my beer. I do this because the yeast will only convert the flavor precursors they created earlier if the beer is warmer than it was when they were created. There is a limit to this rule though since the yeast can only do so much cleanup before they go dormant. Once the yeast go dormant any remaining flavor precursors will be left in your beer to produce off flavors.
|Screwy's Golden Age IPA|