I have a couple of questions about using the hydrometer and when I should remove the wine from the primary fermentation to the secondary fermentation and also after the wine brewing is done. As I take readings I am a little confused about when do you move the wine to the second fermenter. Is it a certain number of days or are we measuring for a specific reading on the gravity hydrometer? On the secondary fermentation I know you are looking for a reading a specific of 0.995. Is that true?
These are great questions. I'm glad you brought this issue up. It seems like the more wine making books you read on this subject, the more answers you will find. Everyone seems to have an opinion, so let's see if I can solidify an answer to your question. What you are essentially asking is:
How do I know when it's time to move my fermentation into a secondary fermenter, and how do I know when the wine's done fermenting?
A short answer to your question is: you should be following the number of days that are called for in the wine making instructions that you have. Simple as that! If your wine making instructions say to move the fermentation into a secondary fermenter like a wine carboy, etc., then do that. This is your best course of action.
But what if I don't have any homemade wine instructions?
Typically, the fermentation will need to be transferred into the secondary fermenter around the fifth day of fermentation. But, not all fermentations are the same. Some ferment so hard and fast, that by the fifth day, the fermentation is done. Others will take much, much longer.
What you are basically doing is transferring the fermentation into secondary when it has slowed down enough so that it won't foam up and out of the secondary fermenter. This is usually around day 5, or when the gravity hydrometer reads 1.030 to 1.020 on the specific gravity scale. This is what happens when everything runs as planned.
However, there are times when the fermentation is still foaming too much to go to the secondary carboys when it's time. In these instances you should wait until the foaming lowers enough that it can safely go into the carboys without making a big foamy mess through the air-lock.
Conversely, there are also times when the fermentation is going so slow that it might be 2 or more weeks before the fermentation will reach 1.030 on the hydrometer. In these instances, you must figure out why the fermentation is going so slow. The article, Top 10 Reasons For Fermentation Failure, that is listed on our website should give you some insight into this.
If after a couple of days you're attempts to re-invigorating the fermentation are unsuccessful, go ahead and put the fermentation in the secondary fermenter anyway, and let it finish out it's long, slow journey to becoming wine.
To answer the second half of your question...
The only real way to know if a fermentation is complete is to take a reading with gravity hydrometer. You are looking for a reading of .998 or less on the specific gravity scale. I've seen fermentations end as low as .988, but this is rare.
Most importantly remember, just because the fermentation activity has stopped does not necessarily mean the fermentation has completed. All you know for sure is it has stopped, so be sure to have a gravity hydrometer reading to depend on for verification of a complete fermentation.
Happy Wine Making,
Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.