Opinion
Black-wrapping and green bottles
Watermark Consultancy’s Mike Hurst responds to a query about black-wrapping and algal growth on empty bottles.
Your bottling plant staff could be missing a greater proportion of greened bottles than before because the green colour has faded or disappearedMike Hurst
Question: Can you help us? We’re mystified by a green bottle problem we’ave recently encountered. We’re an independent bottler supplying several distributors. Over the past few years, we’ve realised that the number of green bottles we’ve discarded has been notably higher among a couple of distributors with the rest. We suspected that it was the way that they were storing, handling and transporting the bottles, so we introduced a blanket requirement that all our distributors black-wrap their empties before returning them to us.
At first, all seemed well, as we found that we were rejecting significantly fewer bottles. But then we found that, last summer, the percentage of complaints received from customers increased quite a lot. What can we do?
Mike Hurst: I congratulate you on raising this issue in the cold months, as it’s so easy to forget green bottle issues now, because they tend not to occur in low sunlight and cold temperatures.
I must say that while there may be a number of reasons for your experiences, there’s one factor that I’ve encountered before, which is the most obvious cause of your problem.
Black wrap does indeed prevent used empty bottles in store from becoming green from exposure to sunlight, provided they don’t have algal growth already. However, if bottles are already showing signs of greening when they’re wrapped, then the green colour will fade or disappear in the dark. The algae do not die, but just lose their green colour. There’s nothing mysterious happening here, as all plants react like this. I can remember carrying out simple experiments at junior school that involved covering up green leaves with card templates and waiting for the white patterns to appear in the shape of the templates.
Your bottling plant staff could be missing a greater proportion of greened bottles than before because the green colour has faded or disappeared. You’ve noted that rejects are down. Could this be the reason? In consequence, your bottle washer is more likely to have become contaminated by algae, causing the number of complaints to rise.
I’m afraid that while black-wrapping is beneficial in reducing the incidence of greened, empty bottles, it does lead to false confidence and complacency on the part of the distributor and bottling plant. At some bottling plants, I’ve seen many dozens of black-wrapped racks of empty bottles left out in the sun for long periods in order to save on interior storage space, with no attempts made to manage the storage period or even to take the oldest rack first.
I must remind you that BWCA and EPDWA bottling codes require that empty bottles awaiting washing be covered and not left outside for more than seven days.
I’m noting a trend among companies, in order to reduce the number of delivery journeys, to deliver water (and pick up empty bottles) maybe as little as once a month. This is bound to mean that some customers will leave empties outside or in uncontrolled conditions for lengthy periods. As a consequence, I’m sure that the number of spoiled empties is going to rise. Some bottles may not be washed for many weeks after they’ve been emptied, which will increase the chances of bottle greening.
What to do
- Hold a meeting with your distributors and ask them to inspect returns before they pack them and send them back to you. They should ensure that they do not wrap already green bottles, and keep green bottles for disposal in a separate area. It would also be useful if they could indicate that the bottles are for disposal, so that your staff don’t have to inspect them again.
- Review the way in which they collect and store returns. I’m sure that all responsibility for the issues raised doesn’t rest with you.
- Review your storage and handling procedures. Don’t let numbers of bottles awaiting washing build up. Stress to your staff that they must restrict the length of outside storage by washing the bottles stored outside for the longest first.
- In your case, I suggest that maybe one week outside storage is too long. Aim for three days.
- Continue with black-wrapping, but do it properly.
- Ask your staff to be more careful in inspecting bottles for greening. Warn them that some algae may have turned pale green, brown or even white by the time they see the bottle. If in doubt, throw it out!
- Just in case there are other factors, review how you run your bottle washer. In particular, wash at 60°C at least. If you can, go up to but not beyond 70°C.
- Drain, clean and sanitise your bottle washer every day.
Green bottles can cost you customers, so take this seriously.
Mike Hurst is consultant microbiologist for Watermark Consultancy
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