My family has been making wine for generations and unfortunately all we have to show for it is some of the world's strongest vinegar. The wine we make is all I'll drink (if I'm at a restaurant I feel like I'm drinking grape juice) but it has a year's shelf life and then it's just a memory. My Uncle and I have wanted to experiment with preservatives for a long time, but my Father is in charge of the "operation" and is vehemently opposed to it. I think he would perhaps be more willing if I were able to present him some facts. Is it possible to add preservatives to one bottle or must they be mixed in with the entire barrel? Also, we make mostly (red) Zinfandel, what should we use?
Is the wine made or stored in a barrel? Are you using the same barrel each year? Do you keep the barrel topped up? If you are using an infected barrel, that may be your problem.
The barrel we use is not infected, and for a year the wine is delicious. After a year, however, it starts to become vinegar as all wine naturally does. I was just curious as to which preservatives should be used, how much of them, when, etc. etc. to keep at least one bottle from every year.
That's not necessarily the case. Wine needs contact with oxygen to turn to vinegar. It also needs the presence of acetobacter. Once a barrel has acetobacter in it because the wine in it turned to vinegar that barrel will try to make vinegar every time you put wine into it. The bacteria gets into the pores of the wood and it's impossible to get it all out. That barrel is then only good for making vinegar.
Assuming for a moment that you have a _clean_ barrel, i.e. a new barrel or one that has no such infection, it is _possible_ to make good wine in it without the use of preservative (sulfite). It isn't easy though, and it requires careful attention to details. The barrel has to be kept COMPLETELY FULL at all times during the aging process, right up to bottling. That means opening the bung a couple of times a week, replacing the wine that is lost by evaporation and bunging the barrel _tight_. That's to keep air from being in prolonged contact with the wine. Acetobacter (and all the other bugs that try to attack the wine) need air to propagate. Keeping the barrel plumb full cuts off their air supply. This also applies to the extra wine you use to top the barrel with. No headspace can be permitted in the topping wine either. That will require you to use a series of progressively smaller containers to store the topping wine between uses, so that you can maintain all of them full too.
If your family is of the custom (as many are) of drawing wine out of a tap in the head of the barrel over the course of the year, that's your problem. Whatever you pull out of the tap is being replaced by _airspace_ inside the barrel, on top of the wine. That space is a playground for spoilage organisms. At first they grow on the surface of the wine (and on the surface of the barrel above the wine) and you won't taste their presence at the tap. Over the course of months the wine from the tap will begin to not taste so good. Eventually it will have quite a lot of noticeable vinegar flavor, and at some point it will only be fit to put on your salad! BTW, if that is representative of your situation, that barrel is only fit for firewood now.
I was just curious as to which preservatives should be used, how
That requires a complicated answer. First off, the preservative you want to use is sulfur dioxide. It's conveniently available for winemaking as potassium metabisulfite, which is approximately 50% available sulfur dioxide (SO2).
Off the top of my head I'd say 50 parts per million free SO2 is what you should maintain in the wine at all times, from crush to bottling. That's not as easy as it sounds because when you first add it to the wine some of it becomes permanently bound to various things in the wine, and is therefore not available as "free" SO2. If you add 100 parts per million (ppm) at the crusher, the next day you may measure only 50 ppm free in the must. After that, however, any more you add will increase the free in a linear fashion.
It gets more complicated. During the course of barrel aging the free SO2 slowly decreases. That's because it's doing its job of scavenging oxygen from the wine, and in the process it gets used up. Every few months or so you need to measure the free SO2 and bring it up to where it needs to be to protect the wine. You shouldn't just arbitrarily dump more in though, because over sulfiting the wine makes it taste and smell bad, and it may bleach some of the color out too.
To do it right, you need to know the pH of the wine _and_ the free SO2. The correct level of free SO2 depends on the pH of the wine. E.g., if the pH measures 3.20 you need 20 ppm free SO2 to protect the wine. If the pH is
3.40, you need 40 ppm free SO2.
There are inexpensive devices for measuring free SO2. They're called "Titrets", and you can get them at a homebrew shop. I'd suggest that you borrow the use of a pH meter rather than investing in one. A local community college's chemistry department might be willing to help you out there. Also, I'd recommend that you get a book on home winemaking and read up on the subject. Jon Iverson's book is pretty thorough, and there are others as well. Good luck!
Are you bottling the wine from the barrel or simply pulling enough out occasionally as needed? If you are just pulling out from barrel as needed and not topping up the barrel and after a year your wine is vinegar, then you DO have an infected barrel.
Consider sulphiting your wine. The link below is one of the best on the topic.
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