Oxygenation is the injection of oxygen into the wort during the brewing process, usually after cooking and cooling, but before fermentation.The effect of boiling the wort is to remove most of the oxygen in the solution.
However, the rapid multiplication of yeast in the wort, i.e. in the “log phase” (ie late fermentation or after fermentation of the beer), requires a lot of oxygen.Without enough oxygen, the yeast cannot reproduce adequately and will not ferment fully.
Saccharomyces cerevisiae is a facultative microorganism that grows and reproduces under aerobic conditions, and performs alcoholic fermentation under anaerobic conditions.
The yeast needs to multiply to a certain number before entering the fermentation stage, which requires oxygen.Therefore, it is necessary to supply oxygen to the yeast by passing sterile air into the cold wort, so that the dissolved oxygen in the wort reaches 8-10 mg/l.
In order to enhance the dissolving effect of air in the wort, very fine air bubbles must be introduced and mixed with the cold wort in the form of a vortex.To make the dissolved oxygen in the wort reach 8 ~ 10mg/I.
In theory, about 3L of air is needed per hectoliter of wort, but in actual production, 10 times the amount is required.Because a part of the air is not dissolved and overflows, the distribution of the incoming air is not completely uniform.
In addition, with the increase of wort temperature and concentration, the solubility of oxygen decreased.
The oxygenation device for wort is generally installed at the outlet of the cold wort of the plate heat exchanger.After the compressed air is decompressed, it enters the wort oxygenation device through the air flow meter and air filter, so that the wort and air are fully mixed and then enter the breeding tank or fermentation tank.
There are many kinds of wort oxygenation devices, the most commonly used is the Venturi tube.
How to correctly control the oxygenation method and oxygenation amount of cold wort
Oxygenation of cold wort seems to be a very simple process, but the control of oxygenation method and oxygenation amount of wort can affect the normal fermentation of yeast, the smoothness of production process, the quality stability and flavor characteristics of beer products.etc. are of vital importance.
Improper oxygenation will inevitably lead to a series of changes in the fermentation process, and even lead to poor fermentation results and flavor defects.
(1) Control of wort oxygenation
The oxygenation amount of wort is controlled according to the degree of oxygen demand of the yeast species and fermentation process used. Different yeast species and fermentation states have different degrees of oxygen demand.
The conventional practice is to control the dissolved oxygen in cold wort at 5 ~ 8mg/L, and make necessary adjustments according to the actual needs of yeast reproduction, generally rarely exceeding 10mg/L.
The oxygenation of wort is generally controlled by the oxygen flow, pressure, time and oxygenation equipment during oxygenation.
The oxygenation effect of wort is related to the control of oxygenation time. The use of unqualified or simple oxygenation devices can not achieve the actual oxygenation effect, and the oxygenation amount is not necessarily proportional to the actual dissolved oxygen content of the cold wort.
In this case, some beer lovers tend to prolong the oxygenation time to ensure the oxygenation effect. In fact, the dissolved oxygen in cold wort is not only related to the oxygenation time, but also related to the wort concentration and wort temperature.
If the wort temperature is low, the original wort concentration is low, and the oxygenation effect is better, and the oxygenation time can be appropriately short. One point; the oxygenation time of wort is related to the oxygenation equipment used, sterile air pressure and flow rate.
The pressure is high, the flow rate is large, the emulsification effect is good, and the oxygenation time can be shorter.
However, the oxygenation time actually controlled by large-scale production is not only combined with the dissolved oxygen content that needs to be controlled, but also with the dissolution and distribution of oxygen in the wort.
For example, batches of cold wort with yeast added are mostly oxygenated throughout, while batches of cold wort without yeast can be oxygenated in different periods, or the oxygenation time is reduced or even no oxygenation.
As long as the amount of dissolved oxygen required for yeast reproduction can be satisfied, over-oxygenation is not recommended. The budding cycle of yeast is about 12h, and it should no longer be oxygenated after 12h. The yeast budding can synthesize linoleic acid by itself.
(2) The control of the oxygenation method has several implications:
One is where the cold wort is oxygenated. The correct oxygenation position should be near the position where the yeast is added, that is, a device that can simultaneously oxygenate and add yeast and fully mix is installed on the cold wort pipeline.
The effect is the best; however, breweries generally use the form of adding a venturi to the cold wort pipeline. Before adding yeast, the cold wort is oxygenated, so that the cold wort containing dissolved oxygen is put into the tank, and then the yeast is inoculated immediately. This is also a better way.
Secondly, during the wort cooling process, a relatively small flow rate can be used to oxygenate the wort throughout the whole process, which can evenly distribute the dissolved oxygen.
Third, all batches of wort with yeast added can be oxygenated in the whole process or in stages, and batches of wort without yeast are not oxygenated in principle; considering the needs of yeast reproduction, multi-batch full tank For large fermentation tanks, the batch of yeast added can be oxygenated in the whole process or in stages.
In the next batch after adding yeast, the oxygenation amount can be appropriately reduced, or the oxygenation amount and oxygenation time can be adjusted according to the yeast reproduction. increase or decrease.
If multiple batches of wort are entered into the tank, the last batch of cold wort entering the tank may not be oxygenated in principle. However, if it is found that the wort into the tank is uneven, it can be filled with sterile air with lower flow and lower pressure for 5-10min.