The Wort and Oxygen

The Wort and Oxygen

The use of oxygen in brewing is a double-edged sword. The yeast need oxygen to grow and multiply enough to provide a good fermentation. When the yeast has first been pitched, whether to the starter or the beer, it first seeks to reproduce. The yeast makes use of the dissolved oxygen in the wort for this. Boiling the wort drives out the dissolved oxygen, which is why aeration of some sort is needed prior to fermentation. The yeast first use up all of the oxygen in the wort for reproduction, then get down to the business of turning sugar into alcohol and CO2 as well as processing the other flavor compounds.

On the other hand, if oxygen is introduced while the wort is still hot, the oxygen will oxidize the wort and the yeast cannot utilize it. This will later cause oxidation of the beer which gives a wet cardboard taste. The key is temperature. The generally accepted temperature cutoff for preventing hot wort oxidation is 80F. In addition, if oxygen is introduced after the fermentation has started, it will not be utilized by the yeast and will later cause the wet cardboard or sherry-like flavors.

This is why it is important to cool the wort rapidly to below 80F, to prevent oxidation, and then aerate it by shaking or whatever to provide the dissolved oxygen that the yeast need. Cooling rapidly between 90 and 130F is important because this region is ideal for bacterial growth to establish itself in the wort.

Most homebrewers use cold water baths around the pot or copper tubing Wort Chillers to accomplish this cooling in about 20 minutes or less. A rapid chill also causes the Cold Break material to settle out, which decreases the amount of protein Chill Haze in the finished beer.

Aeration of the wort can be accomplished several ways: shaking the container, pouring the wort into the fermenter so it splashes, or even hooking up an airstone to an aquarium air pump and letting that bubble for an hour. For the latter method, (which is popular) everything must be sanitized! Otherwise, Infection City. These instructions recommend shaking the starter and pouring/shaking the wort. More on this later.

Sanitization So far, sanitization of ingredients and equipment has been discussed but not much has been said about how to do this. The definition and objective of sanitization is to reduce bacteria and contaminants to insignificant or manageable levels. Sterilization is not really possible. The Starter solution, Wort and Priming solutions will all be boiled, so those are not a problem (usually).
One note – Do Not Boil the Yeast! You need them to be alive.

We recommend using a no-rinse sanitizer such as Star-San, One Step, Iodiphor, or something similar. Mix the sanitizer according to the manufacturer’s directions and apply to all equipment that will come in contact with your wort after the boil, and drain as much of the sanitizer solution from the equipment as possible. No rinsing required! Some sanitizers require letting the solution dry before using the equipment, but some can be used wet. Refer to the manufacturers instructions for contact times and drying requirements. One very useful tool for small parts to be sanitized is a spray bottle; you can purchase a spray bottle from your local garden shop or dollar store. Fill the spray bottle with freshly made sanitizing solution and you can spray down equipment as needed during your brew day. Most no-rinse sanitizers require only a few minutes of contact time, which can speed up your brew day!

Clean all equipment as soon as possible. This means rinsing out the fermenter, tubing, etc. as soon as they are used. It is very easy to get distracted and come back to find the syrup or yeast has dried hard as a rock and the equipment is stained. Keep a large container with a solution of P.B.W. or another food grade cleaner handy and just toss things in, clean later.

Rinsing bottles after each use eliminates the need to scrub bottles. If your bottles are dirty, moldy or whatever, soaking and washing in a mild solution of chlorine bleach water for a day or two will soften most residue. Brushing with a bottle brush is a necessity to remove stuck residue. Dish washers are great for cleaning the outside of bottles and heat sterilizing, but will not clean the inside where the beer is going to go; that must be done beforehand. P.B.W. also works very well but must be rinsed carefully. Do not wash with soap. This leaves a residue which you will be able to taste. Never use any scented cleaning agents, these odors can be absorbed into the plastic buckets and manifest in the beer. Fresh-Lemon Scented Pinesol Beer is not very good. Also, dishwasher Rinse Agents will destroy the Head retention on your glassware. If you pour a beer with carbonation and no head, this is a common cause.

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