Preparing a yeast starter
The reason for using a yeast starter is quite simple. We simply need to outnumber the wild yeast cells and make sure we have a relative short fermentation period.
Preparing Dry Yeast
If it's not showing signs of life (churning, foaming) after a half hour to one hour, your yeast may be too old or dead. Unfortunately, this can be a common problem with dry yeast packets, especially if they are the non-name brand packets taped to the top of malt extract beer kits. Using name brand brewers yeasts like those mentioned previously usually prevents this problem.
Re-hydrating Dry Yeast
Note: Lallemand/Danstar does not recommend proofing after rehydration of their yeast because they have optimized their yeast's nutrional reserves for quick starting in the main wort. Proofing expends some of those reserves.
Preparing Liquid Yeast
Making a Liquid Yeast Starter
1. Take the yeast packet out of the refrigerator and let it warm up to room temperature. If it is a smack pack, place the packet on the countertop and feel for the inner bubble of yeast nutrient. Burst this inner bubble by pressing on it with the heel of your hand. Shake it well. If you are not using a smack pack, proceed directly to step 3. You will be making two successive starters to take the place of the mini-starter smack pack.
2. Put the packet in a warm place overnight to let it swell. On top of the refrigerator is good. So, just put the packet somewhere that's about 80°F, like next to the water heater.
3. On day two we can make up a starter wort. Boil a pint (1/2 quart) of water and stir in 1/2 cup of DME. This will produce a starter of about 1.040 OG. Boil this for 10 minutes. Put the lid on the pan for the last couple minutes, turn off the stove and let it sit while you prepare for the next step. Adding a quarter teaspoon of yeast nutrient (vitamins, biotin, and dead yeast cells) to the starter wort is always advisable to ensure good growth.
4. Fill the kitchen sink with a couple inches of cold water. Take the covered pot and set it in the water, moving it around to speed the cooling. When the pot feels cool, about 80°F or less, pour the wort into a sanitized glass mason jar or something similar. Pour all of the wort in, even the sediment. This sediment consists of proteins and lipids which are actually beneficial for yeast growth at this stage.
Ideally, the starter's temperature should be the same as what you plan the fermentation temperature to be. This allows the yeast to get acclimated to working at that temperature. If the yeast is started warmer and then pitched to a cooler fermentation environment, it may be shocked or stunned by the change in temperature and may take a couple days to regain normal activity.
5. Sanitize the outside of the yeast packet before opening it by swabbing it with isopropyl alcohol. Using sanitized scissors, cut open a corner of the packet and pour the yeast into the jar. Two quart juice or cider bottles work well, and the opening is often the right size to accept an airlock and rubber stopper. Cover the top of the jar or bottle with plastic wrap and the lid.
Shake the starter vigorously to aerate it. Remove and discard the plastic wrap, insert an airlock or put a clean piece of plastic wrap over the jar or bottle and secure it loosely with a rubber band. This way the escaping carbon dioxide will be able to vent without exposing the starter to the air.
6. On days three some foaming or an increase in the white yeast layer on the bottom should be evident. These small wort starters can ferment quickly so don't be surprised if you missed the activity. When the starter has cleared and the yeast have settled to the bottom it is ready to pitch to the fermenter, although it will keep for 2-3 days without any problems. However, I recommend that you add another pint or quart of wort to the Starter to build up the yeast population even more.
The starter process may be repeated several times to provide more yeast to ensure an even stronger fermentation. In fact, a general rule is that the stronger the wash (more fermentable/higher gravity), the more yeast you should pitch.
When is the starter ready to pitch
A key condition to this recommendation is that the composition of the starter wort and the main wort must be very similar if the starter is pitched at or near peak activity. This is because the yeast in the starter wort have produced a specific set of enzymes for that wort's sugar profile. If those yeast are then pitched to a different wort, with a different relative percentage of sugars, the yeast will be impaired and the fermentation may be affected. Kind of like trying to change boats in mid-stream. This is especially true for starter worts made from extract that includes refined sugars. Yeast that has been eating sucrose, glucose/dextrose, or fructose will quit making the enzyme that allows it to eat maltose - the main sugar of the grain based wort.
Yeast nutritional needs
If you use ion-exchanged softened water for brewing, the water may not have adequate calcium, magnesium, and zinc for some of the yeast’s metabolic paths. Magnesium plays a vital role in cellular metabolism and its function can be inhibited by a preponderance of calcium in the wort. Brewers adding calcium salts for water chemistry adjustment may want to include magnesium salts as part of the addition if they experience fermentation problems. Usually the wort supplies all the necessary mineral requirements of the yeast, except for zinc which is often deficient or in a non-assimilable form. Additions of zinc can greatly improve the cell count and vigor of the starter, but adding too much will cause the yeast to produce excessive by-products and cause off-flavors. Zinc acts as a catalyst and tends to carry over into the succeeding generation—therefore it is probably better to add it to either the starter or the main wort but not both. The nutrient pouches in the Wyeast smack-packs already contain zinc in addition to other nutrients. For best performance, zinc levels should be between 0.1-0.3 mg/l, with 0.5 mg/l being maximum. If you experience stuck fermentations or low attenuation, and you have eliminated other variables such as: temperature, low pitching rate, poor aeration, poor FAN, age, etc., then lack of necessary minerals may be a significant factor.
There are three types of yeast nutrients on the market that can supplement a wort that is high in refined sugars or adjuncts.
- Di-ammonium Phosphate: This is strictly a nitrogen supplement
that can take the place of a lack of FAN.
- Shaking the container, e.g. the starter jar
For the beginning distiller, I recommend the simplest methods
of shaking the starter and pouring/shaking the wort. This method
is especially effective if you are doing a partial boil and adding
water to the fermenter to make up the total volume. Instead of
shaking the wort, you can shake the water.
The last method mentioned method uses an airpump and airstone to bubble air into the fermenter. The only precaution you need to take, other than sanitizing the airstone and hose, is to be sure that the air going into the fermenter is not carrying any mold spores or dust-borne bacteria. To guard against contamination, a filter is used in-line to prevent airborne contamination from reaching the wort. One type is a sterile medical syringe filter and these can be purchased at hospital pharmacies or a your local brewshop. An alternative, build-it-yourself bacterial filter is a tube filled with moist cotton balls. The cotton should be changed after each use.
Aeration is Good, Oxidation is Bad
You should not aerate when the wort is hot, or even warm. Aeration of hot wort will cause the oxygen to chemically bind to various wort compounds. Over time, these compounds will break down, freeing atomic oxygen back into the beer where it can oxidize the alcohols and hop compounds producing off-flavors and aromas like wet cardboard or sherry-like flavors. The generally accepted temperature cutoff for preventing hot wort oxidation is 80°F.
Oxidation of your wort can happen in several ways. The first is by splashing or aerating the wort while it is hot. Other beginning-brewing books advocate pouring the hot wort after the boil into cold water in the fermenter to cool it and add oxygen for the yeast. Unfortunately the wort may still be hot enough to oxidize when it picks up oxygen from the splashing. Pouring it down the side of the bucket to minimize splashing doesn't really help either since this increases the surface area of the wort exposed to the air. Thus it is important to cool the wort rapidly to below 80°F to prevent oxidation, and then aerate it to provide the dissolved oxygen that the yeast need. Cooling rapidly between 90 and 140°F is important because this temperature region is ideal for bacterial growth to establish itself in the wort.
In addition, if oxygen is introduced after primary fermentation has started, it may cause the yeast to produce more of the early fermentation byproducts, like diacetyl. However, some strains of yeast respond very well to "open" fermentations (where the fermenter is open to the air) without producing off-flavors. But even for those yeast strains, aeration or even exposure to oxygen after fermentation is complete can lead to staling of the beer.
To summarize, you want to pitch a sufficient amount of healthy yeast, preferably grown in a starter that matches your intended fermentation conditions. You want to cool the wort to fermentation temperature and then aerate the wort to provide the oxygen that the yeast need to grow and reproduce. Then you want to protect the wash from oxygen once the fermentation is complete to prevent oxidation and staling.