When to use sulphite

You may also be experiencing some reduction problems. Oxidation and reduction go hand in hand. I am not a chemist but my understand is that it is more complex than just "oxidation". Some of the off flavors (metallic as an example) may be the result of reduction reactions taking place simultaneously with the oxidation reactions.

There is some excellent information here:

Although it can look somewhat intimidating at first glance, I think you can get the main points without getting too involved in the science. Just be patient and read through and then go back and get some general information or rules of thumb to help you out. Or, if you want to research the issue in detail, this is a good place to start.

I would recommend that you consider building / buying the kit for testing SO2 levels in your wines and make your sulfite additions based on need and pH - not on recipe. While I'm not convinced that sulfite levels are causal to your oxidation problems, keeping your wines at the appropriate levels of SO2 is your best insurance against various microbial spoilage problems.

I agree that pH is a MAJOR factor along with SO2.

Generally, from my experience, red wines can be handled fairly roughly - splashing at racking (which can be beneficial) etc. as long as the pH is kept around 3.5 and the pH levels maintained for that pH.

There are two schools of thought on early addition of sulfite to white wines. One camp feels it is best not to sulfite must as the browning actually falls out as the wine clears leaving you with a wine lighter in color and resistant to browning since the reactions already occurred. The other camp uses 50 to 100 PPM at crush based on health of the grapes, moldy grapes get the higher dose. I sulfite but have tried the no sulfite avenue too.

Washing grapes - especially if you are depending on natural yeast, is not recommended. Cultivated yeast is cheap, predictable and reliable, using natural yeast could result in a batch not finishing to dryness but it seems to be fine with your wines.

Measuring sulfite levels for red wines requires both a decent calibrated pH meter and an aeration oxidation apparatus; that will run approximately $300 so if you are not looking to jump into that water it's understandable. Titrettes from Chemetrics work fine on whites and are relatively cheap.

Your first rack should be with some splashing; after that racks should gentle with no splashing. If you follow that process you can probably just add 1/8 level teaspoon of potassium metabisulfite per 5 gallon (US) to the wine each rack and will be safe; that is around 20 PPM. As mentioned by others, sulfite additions are governed by pH, higher pH requires more sulfite so a good pH meter is worth having. Since you mentioned your acids are not high you might need 1/4 teaspoon, at least at bottling. That is where the pH measurement would be helpful, a local school's sciences department would have one if you don't want to do that.

Joe

Comment on the cost of an AO apparatus ... I agree that this is one of the more costly items a home winemaker might invest in, but I would argue that it is also one of the more critical tools in a home winery ... knowing the SO2 levels helps the home winemaker manage their wines, and winemaking decisions, such that they can avoid some costly mistakes.

I was able to 'build' a kit for somewhat less than your estimate. Titration stand, beakers, tubes, etc can all be purchased separately from any of the better online science supply houses. And rather than pay for the more expensive vacuum pump, the system can be 'reversed' and a cheaper aquarium air pump used - as long as all the fittings are tight it works just fine (and can be demonstrated to do so by comparative tests with vacuum aspiration kits). Still costs a couple hundred bucks tho, so your point is well taken.

For my $, investing in an AO appartus ranks along with a top-quality pH meter, a good TA titration kit, and a paper chromatography set up as 'essentials' in my winery lab.

Now if I could only figure out how to build an accurate ebulliometer on the cheap!

YUP.........

Michael

That link even intimidates me !! ;o)

Let me see if I can summarize just a little. ;o)

Oxydation - two kinds we are concerned with: Enzymatic and reductive. Enzymatic is fast while reductive is slow(er). Enzymatic is what causes fruit to brown quickly. Cut an apple in half and you can almost see it turn brown. SO2 inhibits/destroys these enzymes. So the more prone the fruit is to this kind of browning, the more important it is to use sulfite at crush. And, by destroying these enzymes, it actually leaves_more_oxygen in the must for the yeast to use to get started. At "aseptic" levels, SO2 also kills things like Bot, Bret, fungus, etc. so you need to use enough sulfite at crush to take care of these things also.

Reductive is pretty much just chemical reactions which happen any time oxygen is present. These happen more slowly and temp plays a large part in how fast these "ageing" reactions take place, but SO2 slows this conciderably, so maintaining SO2 levels up to and into bottling is also important. An "aseptic" level is also important here to prevent certain kinds of microbial spoilage.

Go to that link and look in chapter 7 for chart number 3 and figure number 6. These pretty much tell you the relationships that you need to know to determine dosage required. If you understand that an "aseptic" level is slightly higher than 0.8ppm molecular, you should have no problem using these.

Memory ain't what it used to be. Hope others jump in and add to this. HTH

Frederick

I'm not sure how 50 PPM free SO2 can ever remain post fermentation if normal quantities are used but I guess anything is possible... My assumption is there is no free sulfite remaining after a healthy vigorous fermentation.

I think a little sulfite will do you a world of good here. There is another form you may want to consider given your container size; Campen Tablets are readily available and might be more convenient.

Joe

The use of suphite for the protection of your wine is all dependant on the style and future consumption of your wine. If you want a wine to last longer in bottle you are going to require an addition of sulphite to protect your wine. When to add sulphite it depends on pH and the use of indigenous yeasts. THe lower the pH the less likely you will suffer oxidation issues. The lower the temperature of storage the less oxidation issues you will have. The less ullage in your filled bottles the less oxidation you will have. Ullage is the amount of airspace in your bottle. Use a combination of these when storing your wine and it will last longer. Because you are not using a foregien yeast i would not reccomend using sulphites before fermentation because this will limit your sucess during fermentation. However it is very important that you use sulphites immediately after fermentation finishes or just before the end of ferment if you want to retain some residual sugar. This is the most important time to protect your wine from oxidation and thus prevent future oxidation. It is essential you know your sulphur levels so the sulphur kit is also good advice. At bottling i reccomend at leat 15-20ppm of free SO2. Maybe a little higher because your probably not bottling with an inert gas cover. Its ok to oxidise before fermentation even hyper oxidation has shown to have merits but after primary fermentation especilly if you not going through Malo you must use sufficient quantities of Sulphites to protect your wine and monitor its progression, ie if you rack you will lose some free SO2 thus making your wine more susceptible to oxidation, good luck and great wine, SDH Bachelor of Viticulture and Oenology

Thanks for that very clear piece of advice.I probably will continue to wash the grapes,ferment on natural yeast and add sulphite after the fermentation has finished,just as you describe.I tend not to bottle but rack the wine into 1 gallon demijohns-at this point I intend to sulphite.One final point.When you say add 15-20ppm of free SO2,is that very approximately 0.5 Campden tablet/gallon or 0.1g of metabisulphite/ gallon?I am a little confused after reading all the science about molecular SO2,free SO2,total SO2,bound SO2. Thanks again Michael

Another alternative. Buy a bottle of Campden tablets and follow the instructions on the bottle (eg. 1 tablet per gallon). Problem solved......... :o)