Frequently Asked Questions

Frequently Asked Questions

What is the legal limit of sulfite residue?

This is a broad question but focussing on the legislation in effect within the EU (Referred to as Harmonised Legislation, meaning all EU and EEC members use the same rule set) and only looking at table grapes, blueberries and litchis; MRLs (Maximum residue levels) are set at 10ppm (parts per million), meaning more than 10 ppm detected on fruit within a commercial channel (Earmarked for fresh consumption as the next phase) is more than the allowed level, thus illegal. Less than 10ppm is allowable.

Can Uvasys be cut with scissors?

All of our sheets can safely be cut with sharp scissors or knives. 

Because none of our products contain sachets or granules in lose form there are no contamination risk. The only downside to this is that the surface area being treated, which the sheets was designed for, will be affected and the control might not be as desired.


Can the sheet be used upside down?

In the past we have seen producers turning the sheet upside down. Although this is not the recommended use the activation of the sheet will not be affected and the gas response will be similar, although retarded. 

What is the level Uvasys sheets dose SO2 at?

Depending on the product the levels of dosing varies over time and per phase but with the most widely used product, Uvasys Green, there are 2 phases of SO2 release (dual release). The first is a high level of SO2 release within a short period of time – 180ppm over 48 hrs. This kills off active botrytis growths within the confined environment. The second release curve is a slow, trickling, release of SO2 of about 5ppm for up to 120days. This stops latent botrytis growth from developing.

How quickly does SO2 break down in the fruit?

This is a difficult question to pinpoint exactly as there are multiple factors affecting the breakdown curve of SO2 but the below should bring clarity as an answer:

SO2 sulphites (the chemical which presents as the allergen metabolise inside grape berries to form sulfates (salts which is non allergic). The rate at which this happens is incredibly fast (+/- 4 Hrs) and the detail to this study can be found in the following paper:

Metabolic responses to sulfur dioxide in grapevine (Vitis vinifera L.): photosynthetic tissues and berries

Michael J. Considine1,2,3 and Christine H. Foyer1,2,*

The authors found c. 75% of the absorbed sulfites were rapidly oxidized to sulfate with a half-life of 4 h, with most of the remainder oxidizing with a half-life of 20 h…

How do you test for SO2 residues and what does this test look like?

The most common method of testing is the Optimized Monier-Williams method. Most laboratories that offer MRL testing should be able to provide this test as well.

Where in the sheet is the SO2?

Our products does not actually contain SO2 or Sulphur as a raw ingredient. SO2 is generated by means of an autocatalytic chemical reaction between water (H2O) and Sodium Metabisulphate. Please look at the Products page in conjucntion with the Research pages.

Can I use Litchisys on Grapes if I don’t have Uvasys in stock?

This is not recommended. The reason being that Litchisys and Uvasys have different formulations of Sodium Metabisulphite and other components which regulates the release curves. The biggest of these are temperature mapped curves. Because the reaction to produce SO2 is autocatalytic the release curves change when the temperature changes. Different products are not usually stored and transported at the same temperatures and because of this using sheets not designated for the intended produce will not only put you and your product at risk, but also void any warranty we provide.

What is bleaching?

Bleaching occurs when SO2 bonds with water. This is usually on the surface of the produce where condensation formed droplets. When enough SO2 dissolved into these droplets they become acidic, forming a mild sulphuric accid. This in turn then bleaches the affected area and the colour is removed, just like household bleach when spilled onto your favourite jeans.

Is it safe to eat bleached product?

Completely! It just might not taste as expected.

If the release of SO2 is affected by temperature, what happens when there is a mechanical problem with my container?

For each 5 Degree celsius rise in temperature, the SO2 release will double. Usually this will happen during the second phase of the release curve and the effects will be minimal. However, if the temperature during transit jumps dramatically and for a extended period of time, effects will be noticeable. Mostly you will find bleaching and a slight reduction in the window of release. This is very difficult to quantify, and each case should be individually inspected.

I found some old sheets from a few years ago. Are they still good to use or should I throw it away?

Our sheets are VERY durable if stored correctly. Some have been forgotten about and upon testing a decade old product, still worked. The first thing to do is make sure the storage bag is still sealed and intact. If the seal has not been broken, then this is the first bit of good news. Next, find the batch number and forward this to us stating the conditions of storage and integrity of the bags. If needed, we could run tests on our retention samples to simulate expected outcomes.

Disclaimer: This website is for marketing purposes only. All references to values, volumes, timeframes and other variables are guidelines only. If you require precise information please use the contact us page with your query.




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