Ordinarily the first stage of fermentation is carried out in a bucket or fermenting bin. It is possible to kick start your yeast reproductive cycle and boost numbers with a yeast starter and that’s something we’ll look at in more depth soon. The other way is to re hydrate the yeast by adding it to a small quantity of luke warm water, the instructions to do this are almost always on the packet so check that out.
Once the yeast is prepared it is “pitched” into the must (the fruit pulp and sugar) it then begins to reproduce and grow by using the sugar as fuel and after a short lag time which may be up to 24 hours it will begin to foam and bubble with activity. This is what we call primary fermentation and is the first real step towards your alcoholic wine.
This primary fermentation doesn’t last long, around a week or two and at this point we separate the liquids from the pulped fruit and allow the yeast to continue with their activity which will be a lot more sedate now. This secondary fermentation is usually carried out in a carboy or demijohn which protects the wine from oxygen and wild yeast whilst the wine clears.
Transferring to Secondary
After the initial burst of fermentation or the “primary fermentation” has finished we need to move the wine into a demijohn or carboy. There are still processes occurring and the yeast will still be working but in a slower and less visible manner. What usually occurs is the wine is separated from the pulp of the fruit or flowers by straining and the secondary fermentation continues in the demijohn with an airlock fitted.
Straining can be as simple or hard as you make it, depending on the flavour of the wine or the fruit, flower or flavouring used you may be able to strain the wine with something such as a sieve or a fine straining bag may be necessary. The goal is of course to remove as much of the pulp or debris as possible. In some cases where a fruit has been pulped finely it may be a good idea to strain the wine twice, firstly with a something with fairly large holes to remove the bulk of the pulp then through a finer strainer to remove the smaller particles.
What’s Going On During Secondary Fermentation
The yeast will at this point have consumed most of the available sugar and nutrients available to them and will be now cleaning up and evening out the flavour of your wine. During the first stages of fermentation yeast creates compounds that although necessary for their growth and function aren’t that great when you taste them. Allowing the yeast this secondary phase of fermentation gives them the chance to removes these undesirable compounds and flavours and gives us a better wine.
There is also the fact that the wine will at this point be very cloudy and there is no way you should be bottling it at this point. This time in the demijohn will allow it to slowly clear.