Using Sanitizers in Wash Water: Part 3 - Correct Use of Sanitizers
Food safety considerations are critically important during and immediately after washing fresh fruits and vegetables.
Parts 1 and 2:
- [Voiceover] This is the third and final video on our series on using sanitizers in wash water.
In the first two videos in this series, we discussed reasons for washing fresh produce, and types of wash water systems.
In this third video, we will focus on the selection and correct use of sanitizers.
Part three, correct use of sanitizers.
Let's start with a look at the legal aspects of sanitizers for wash water.
The United States environmental protection agency, or the EPA, regulates sanitizers that come in contact with food, the same way it regulates pesticide.
If you are in the business of selling fresh produce, you are required by federal law to use only certain sanitizer formulations and concentrations that have been approved by EPA for washing fruits and vegetables.
You cannot mix up your own, or substitute other formulations, you must use approved sanitizers according to the directions on the label.
As we say in our pesticide education presentations, the label is the law.
What are some of the wash water sanitizers that we see on the market?
There are three main types.
The most common are chlorine sanitizers, the active ingredient of chlorine sanitizers is hypochlorous acid, and this is also widely used in household bleach products.
The liquid forms of bleach contains sodium hypochlorite, while the powder forms contain calcium hypochlorite.
A second and chemically related type of sanitizer is chlorine dioxide.
Chlorine Dioxide can be purchased in two forms.
A gas which is injected into the wash water, or as a chemical solution that you activate by mixing in water.
There are many commercial suppliers of chlorine dioxide products that can help you pick the right one for your operation.
And finally, there are the sanitizers that contain peroxyacetic acid, either by itself or in combination with hydrogen peroxide as their active ingredients.
These formulations are chemically similar to vinegar, and the hydrogen peroxide you might have in your medicine cabinet, but remember, it is not legal to mix up your own sanitizer, you must use products labeled for this use.
Many of these products are OMRI approved, so they can be used by certified organic farmers.
When used properly and according to label directions, all of these sanitizers are very effective at lowering microbial populations in water.
Regardless of the type of sanitizer you choose, we strongly recommend that you work with a chemical supply company to find the best one for your operation.
Because chlorine or bleach sanitizers are most common, we will use these products to illustrate the general principles for the legal and effective use of sanitizers.
And we'll also pull out a few important details about the two other types of sanitizers.
We've all seen bleach products and other sanitizers available in stores for household use, such as for whitening laundry, or disinfecting kitchens, or bathroom surfaces.
But most of these products are not acceptable for use in wash water, because they are not labeled for food use.
So how do we know if a sanitizer is legal to use, and is effective for our disinfection purposes?
Here's an example of the label on a chlorine sanitizer.
In this case, it's a Clorox product.
We know that this is an acceptable product for use for produce wash water disinfection, because it has an EPA registration number printed right on the label.
This one says EPA 5813.
When you see an EPA registration number on a product, that means the manufacturer has conducted research studies to determine that it is effective when used within concentration limits established by federal regulations.
The directions for use are usually clearly printed on the label, or a supplemental label document.
Here's a closer look at the label for a Clorox Germicidal product.
You can see the EPA number as well as specific directions for washing fruits and vegetables.
In this case, the directions say to add the produce into water containing 25 parts per million of the sanitizer, and allow it to stay submerged for two minutes.
Remember, it's a violation of federal law to use a product in a manner different than what the label indicates.
We see a lot of consumer fruit and vegetable washes on the market right now.
But if you read the label, you'll see that almost none of these products are effective for killing microorganisms.
IF they were true sanitizers, the label would have to indicate that they were approved by the EPA.
And they would have an EPA registration number on the label.
To understand which sanitizer is appropriate for your operation, it's important to understand a little bit about the chemical and physical properties, and how those may affect how you can use the sanitizer.
Of course, cost will be an important factor to consider as well.
Let's return to the chlorine sanitizer that we discussed previously, and take a closer look at some of its properties.
In the case of chlorine, we know its effectiveness in killing microbes will vary depending on a number of factors.
One factor is the pH, or the acidity of the wash water.
The graph on the left shows chlorine sanitizer activity as pH changes from a low of four, very acid, to 10, very alkaline.
As shown in the graph, if we raise the pH too much, most of our chlorine is going to be in the inactive form, where it has no antimicrobial activity.
If the solution is too acidic, toxic chlorine gas can bubble off, and no one wants that.
So we're generally looking for a pH between six and 7.5 where there's still plenty of active chlorine.
It's a good idea to test the pH of your wash water to make sure that it is in the optimal range for a chlorine sanitizing solution.
Another factor affecting chlorine activity is the amount of organic matter, such as dirt, dust, and debris in the wash water.
Chlorine is especially prone to binding with organic matter, which can reduce its effectiveness.
When we add chlorine to our wash tank, it is initially in what we call the free form.
This form has the highest antimicrobial activity, when free chlorine reacts with organic matter, we call this form bound chlorine.
Bound chlorine has much less antimicrobial activity, that's why it's really important to get as much soil and other accumulated organic matter off the surface of produce before adding it to the wash tank.
We should note that usually, there is both free and bound chlorine in solution.
We call the sum of the free and bound chlorine, total chlorine.
Other characteristics of chlorine you should know, are that it can be corrosive to some metals, and it is irritating to the skin.
There are also some concerns about potentially toxic byproducts, so we want to use the minimum amounts necessary to meet our disinfection goals.
Chlorine dioxide sanitizers are similar to chlorine sanitizers, but they do differ in some important ways.
Chlorine dioxide has greater oxidizing power, and is used at lower concentrations, and is very economical.
Chlorine dioxide is less sensitive for pH changes, and also to organic matter in the wash water.
Chlorine dioxide must be activated on site, so it's somewhat more difficult to use.
Like chlorine, chlorine dioxide is corrosive, and can off-gas if handled improperly.
Sanitizer products that contain peroxyacetic acid with or without hydrogen peroxide, are generally more expensive than chlorine, or chlorine dioxide, but there are advantages to using them.
They are not sensitive to pH, or to organic matter.
They are not corrosive, and they're non-irritating when used at the proper concentrations.
Finally, their byproducts are nontoxic.
Now that we have compared the properties of the three types of sanitizers, let's return to chlorine as an example of a commonly used sanitizer.
So how much chlorine do you need to use?
Well, you don't need a lot of free chlorine to kill bacteria in water, just a few parts per million, as long as our pH is somewhere between six and 7.5.
But often you will see the label specify higher concentrations, something in the range of 50 to 150 parts per million.
We add extra chlorine to wash water because we know the concentration of free chlorine will decrease once we add produce to the tank, and we don't want it to get so low that it's no longer effective.
How quickly the free chlorine will decrease depends on the type and the amount of produce you're washing, how soiled the produce is, how often you change the wash water, this is why it's important to monitor free chlorine in wash water.
Here's an illustration that shows how free chlorine concentration can decrease during washing as organic matter builds up.
If you look at the bottom of the drawing, you can see the type of batch wash system we described in the last video.
Note that each picture shows what would happen over time if produce is added to the tank for washing.
The produce is removed, and a new batch of produce is added to the same wash water.
In this example, the wash water is not drained between each batch, it's used over and over again.
At first, our sanitizer concentration is at its highest value, and the wash solution contains very little organic matter.
The wash water is clean, with no evidence of cloudiness or turbidity.
But once we add produce, we can see that dust, soil, anything else adhering to the produce, accumulates, and the level of turbidity goes up, as shown by the green line.
At the same time, the active sanitizer concentration shown by the red line decreases.
That's happening because the sanitizer is increasingly bound to the organic matter, and becoming less effective.
So the problem here is that the sanitizer will do its job for the first batch, but by the time we get into the fourth load and beyond, the sanitizer has little or no effect.
So if you're using a sanitizer in a batch system where the water is reused, you need to know how much chlorine to initially add to the tank, and then monitor the concentration over time to determine when you should add more sanitizer or dump the entire contents of the tank and start all over with a fresh solution.
Once we have prepared our wash water solution, it's a good idea to verify that we have added the right amount of chlorine.
You may find that you have to dilute the wash water a bit or add more chlorine to get in the right range.
When the successive batch system we just described is used, it's especially important to periodically monitor chlorine levels.
There are a number of methods that can be used for this purpose, including test kits, or small paper strips that change color depending on the concentration.
Color changing strips or electronic meters are also available to test for pH.
From what we've discussed about the difference between free and bound chlorine, it follows that a measurement of total chlorine might not be a good representation of antimicrobial capacity in the wash water.
To get the best determination of how effective our wash water is, we need to use monitoring strips that measure free chlorine.
This will help us determine when to add more sanitizer or change the wash water.
Interpreting test kits for paper strip color changes can be tricky at first, but it should get easier with practice.
You can also use an oxidation-reduction potential meter, also called an ORP meter, to measure sanitizer effectiveness.
ORP values increase when the free chlorine levels rise, so you can determine what ORP value represents a sufficient free chlorine level.
This can be a lot quicker than test kits and color strips.
You just dip the probe in the solution and read the ORP value.
ORP meters work better for some sanitizers than others.
Read the instructions that come with your meter carefully.
Finding a source for the right sanitizer for your operation is not always easy.
One information resource is the National Pesticide Information Retrieval System.
You can follow the link shown here at the bottom of the video, or just do a search for NPIRS.
And you can type in a product name, and it will list manufacturers of those products for you to contact.
And again, it's really important to establish a relationship with your chemical supply person.
You can also talk to your local farm store and ask them if they can stock a specific product you are looking for.
This is the last video in our wash water series.
To review, we identified some different sanitizers, and focused on chlorine to illustrate the importance of following government regulations, following label directions, and monitoring sanitizer concentrations throughout the washing process to make sure we are killing microbes.
For more information, please visit Penn State's farm food safety site, extension.psu.edu/food/safety, and click on farm and food safety.
Our site is also a good source of information on good agricultural practices and post-harvest practices.