We get this question a lot so we thought we would discuss it here. [Note: Most of this information is available on our troubleshooting guide under SO2 Problems]
There’s two situations that may cause concern about the reading.
Your instrument indicates an endpoint (beeps) right away, either before adding any SO2 Titrant, or after adding just 1 or 2 drops.
Your instrument apparently never indicates an endpoint, even after titration with a large amount of the SO2 Titrant.
Situation (1.) happens a lot. Most of the time, this is just the normal endpoint response, telling you that your wine’s ppm of free SO2 is zero. To verify that the endpoint indication is valid, add 1 drop of 10% KMBS and stir. The signal should drop to below 50 right away, and the endpoint indicators should stop signaling. If the endpoint signaling does not stop, you may have a problem with the instrument.
Situation (2.) also crops up from time to time. Let’s say you are running an SO2 test on your wine and you use the ENTIRE 5mL syringe of SO2 Titrant, but your instrument stays on 0.00 or a low number, indicating that you still haven’t reached the endpoint. This would normally mean you have over 100 ppm free SO2 in your wine. But you’re pretty sure there isn’t that much SO2 present. So your instrument must not be working, right?
At Vinmetrica, we get a lot of inquiries about the acidity of wines and how to measure them. We have a blog on pH & TA here (and followed up here) on our website wherein you can find detailed discussions about various aspects of this subject. Here I’d like to touch on a few of these.
pH vs TA
pH is a measurement of the free hydrogen ion concentration (OK, actually it’s activity that is measured; close enough…but see below). Titratable acidity TA, on the other hand, measures the total amount of hydrogen ion available in free and bound forms. pH and TA both correlate to the tartness of the wine, but the kind of acidity the wine exhibits is generally more a function of its TA value. The pH value is important for taste as well, but more important is its effect on stability of wine, from the beginning of fermentation through to the final product. Very roughly speaking, we want our whites and rose’s to be in the pH range 3.1 to 3.4, while our reds are usually best in the range 3.3 to 3.7. And in general we’re hoping that our TA values are going to be 6 to 7 for reds and 6 to 9 for whites. Note that pH and TA of wines do not track each other in any consistent way. For example it’s possible for a low pH wine to have a low or a high TA value.
For those us of in the northern hemisphere it is time we start getting ready for harvest season!
WineMaker Magazine has a great Harvest Check List in their most recent edition, written by Bob Peak. It is wonderfully detailed and a must read for all our customers. It is an all encompassing check list whereas ours will just scratch the surface. Our checklist reflects only what we do here at our own winery. What you do during your own harvest is up to you.
We always use a checklist to prepare and to ensure we have everything we need for a successful harvest. Our winery, Little Oaks Winery, is a small operation with a limited about of employees and we have found that preparing for harvest is essential for producing award-winning, memorable wines. Our winery is about four to five weeks away from harvest time. It’s time to start preparing.
Wine is an acidic substance, and there are ranges of acidity that are appropriate to each varietal. In general a wine that is too acidic will taste sharp or sour, while one that is not acidic enough will taste flat and insipid. It’s no surprise to those of you on the quest for great achievements in winemaking that pH and acidity (TA) are important aspects that are key to know and control. In a previous issue of The Wine Analyst’s Blog (April_pH_Blog), we discussed pH and how it’s measured. In this issue of The Wine Analyst’s Blog, we’ll learn more about pH, TA, and how to understand and manage them in winemaking. We’ll also look at yeast assimilable nitrogen (YAN) which uses the TA system. Keep Reading More!
For years it has been said that the Ripper method for measuring sulfite (SO2) has one drawback: interference from “reductones”. These are substances that react with the iodine titrant as SO2 itself does, causing an overestimation of the true SO2 level. But as we’ll see below, this does not seem to be a huge problem with the Vinmetrica version of the Ripper method, and where encountered, it can usually be corrected for.
The Ripper method uses iodine or iodine-generating reagents to oxidize the SO2 in the test sample (primarily wine, but beer and cider are also examples). It relies on the quantitative reaction of iodine (I2) oxidizing the SO2 in the sample under acid conditions.
In this reaction, SO2 is acting as a “reductant” for the oxidant iodine. When all the SO2 is oxidized by iodine at the endpoint, excess iodine appears in solution. The Vinmetrica system detects this event as a sharp rise in electrochemical current with its SO2 electrode.
Anything in the sample that reacts like a reductant – called a “reductone” – in a Ripper titration will appear to be SO2, leading to an overestimation of the SO2 level. A well-known example of a reductone is ascorbic acid. Ascorbic acid (“AA”, also known as ascorbate or vitamin C) reacts with iodine just as SO2 does, that is
Ascorbic acid can be found in modest amounts in some vinifera varietals, and it can occur in high levels in a number of fruits, like citrus and some berries. When trying to measure SO2 levels in these samples, one must be careful not to get misled by ascorbate parading as SO2!
There are other things present in wines and juices that can act as reductones. In principle, reducing sugars (glucose, fructose) and various polyphenols could act as reductones.
Summary: Vinmetrica is participating in the CTS Wine Industry Interlaboratory Program this year. Along with 100 other labs, we tested two samples from CTS for up to 16 parameters. Using our products, we obtained results for free and total SO2, pH, TA, malic acid, and residual sugar that were in good agreement with those of the other participants.
We are pleased to report the first round of results from participating in Collaborative Testing Services’ (CTS) Wine Industry Interlaboratory Program for 2020. CTS (www.collaborativetesting.com) provides samples to, and analysis of the results from, participating laboratories in a wide variety of testing technologies. The Wine Industry Interlaboratory Program focuses on chemical and physical analysis of wine.
This last round of samples from CTS (“Cycle 065”) comprised two sweet red wines. About 100 labs across the US participated. The following parameters were available to be measured and compared: Total SO2, Free SO2, TA, pH, Residual Reducing Sugars, L-malic acid, %ABV, Specific Gravity, Glucose + Fructose, Copper, Potassium, A420, A520, L-lactic acid, Conductivity, and Methanol. We submitted results for all these except Copper, A420, and A520, the first because we don’t have the equipment for it, the latter two because we rarely perform them (though we can do so). Keep Reading More!
There are several reports comparing various methods for determining free and total sulfites (SO2). Aeration oxidation (AO) and Ripper titration methods (like Vinmetrica, Hanna, and old starch color change techniques) are the most commonly employed. In addition there are a number of methods based on spectrophotometric techniques or color reactions that have come into use in recent years. Here I want to focus on the performance of the AO and Ripper methods vs. others, and vs. each other.
We have generated lots of our own data comparing AO and Vinmetrica’s SO2 test, and we know without any doubt that, with the exception of exotic samples (like wines made from ascorbic acid-containing fruit), the Vinmetrica system produces results that are indistinguishable from those of the AO method. But I think it’s time to revisit the information that’s out there on others’ assessment of the comparison of these techniques. Keep Reading More!
As many of you know, Winemaker Magazine (WMM) is a great source of information and techniques for the serious home winemaker. This weekend many of us planned to attend the annual WMM Conference that was to be held in San Luis Obispo amid one of our favorite wine regions, the California Central Coast. In the interest of public health and safety, the meeting has been postponed. As of this writing, it is to be held next year May 20-23 in the same location. So we’re looking forward to that!
The Vinmetrica Team would have been at the WMM Conference to share information about our products and to learn more about your needs. We can’t all meet this year, but we can provide the same discount codes for a brief time as we do every year at the conference!
If you order anything on-line from Vinmetrica before midnight on Sunday, you can take 15% off your entire order by entering this discount code Keep Reading More!
On the quest to fashion the best wines, we make multiple measurements to ensure that our wine ferments and ages properly. We know that it’s important to keep our SO2 levels up; knowing the pH and acidity of the wines is essential to SO2 management as well as proper stability and flavor. If we’re doing malolactic fermentation, we need to measure malic acid to know when that step is complete.
At some point prior to bottling, you’ll likely want to know the levels of residual sugar (RS), as this will impact your preparation for bottling. If you’re selling your wine, you need to measure your wine’s alcohol by volume (ABV); and even if it’s for your own use, it’s good to know the alcohol level, if for no other reason than to be able to prove you are on top of your process from vineyard to bottle. In the last few years, Vinmetrica has released two new kits for assessing these post-fermentation parameters. The Residual Reducing Sugar test and the Vinmetrica ABV kit are accurate and simple procedures for home winemakers and small wineries. Keep Reading More!
By now you know that Vinmetrica has the reputation for providing simple, low cost, fast and accurate tests for winemakers…tools that let you make the best wine you can. In this installment of the winemaker’s blog, we’d like to give a brief account of our origins. Keep Reading More!