Using Sanitizers in Wash Water: Part 2 - Types of Wash Systems

This series of three technical videos provides detailed information on best practices to maintain produce quality and safety following the harvest of fresh fruits and vegetables.
Using Sanitizers in Wash Water: Part 2 - Types of Wash Systems - Videos


The need for adding sanitizers to wash water depends on the type of wash system used.

Parts 1 and 3:

Using Sanitizers in Wash Water: Part 1 - Reasons for Washing Fresh Produce

Using Sanitizers in Wash Water: Part 3 - Correct Use of Sanitizers


Tracking Listeria monocytogenes in produce production, packing, and processing environments Food safety validation of mushroom growing, packing, and processing procedures Farm food safety, Good Agricultural Practices (GAP) training Hazards Analysis and Risk Based Preventive Controls (HACCP) training Technical assistance to home and commercial food processors Food Safety Modernization Act (FSMA)

More by Luke LaBorde, Ph.D. 

Lee Stivers

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- [Narrator] This is the second of three videos in our series on using sanitizers in wash water.

In the first video of this series, we discussed reasons for washing fresh produce.

In this second video, we're going to talk about some types of wash water systems.

And in our final video, we will be taking a closer look at sanitizers and how to use them correctly in wash water.

Part two, types of wash systems.

Let's start by reviewing some types of spray-wash systems for fresh produce.

The first type is a simple single pass system.

In this system, the produce is sprayed with water from above as it moves along a belt.

The water follows a single path as it passes over the produce and is flushed away into the drain, never to be used again.

In this system, the produce items are not immersed in the wash water, and the chance for the kind of cross-contamination that we discussed in the previous video is low.

Therefore, adding a sanitizer to the wash water is optional.

But that's only if you're using water that is potable.

That means it is microbiologically safe to drink.

But if you are not sure that your water source consistently delivers potable water, it is best to add a sanitizer feed line to your system.

The simplest example of a single pass system is when you wash produce in the sink using a kitchen sink sprayer, as you see in the picture on the left.

The broccoli in the colander is washed with a continuous spray of water which goes directly down the drain.

On the right is another example of a single pass system.

This picture was taken at a small farm in their packing area.

You can see that they have spread out soiled radishes on a screen, for spraying with a garden hose.

The water that carries away the mud is not reused in the washing system.

Here's another example.

This is a lettuce washing system at a small growing and packing operation.

They're washing the lettuce by placing it on the belt and spraying from above, and then the water goes down the drain.

And because it's not being reused, sanitizer is optional.

A grower with more capacity might need a larger system, like this single pass spray wash line.

Here the product moves along on a belt, and water passes over it in a single path.

Because the wash water does not recirculate, addition of a sanitizer is optional in this case.

Single pass systems can use a lot of water.

To conserve water, recirculating wash systems have been developed.

Just like our earlier examples, the water passes over a movable belt.

However, here it is collected in a reservoir at the bottom of the tank.

Then, it is pumped back up to wash more incoming produce.

But because the water is reused, there is an added risk of cross-contamination.

Imagine that one of the produce items is contaminated with pathogenic microbes.

These microbes could wash off and enter the wash water flow.

Here, they may accumulate, and eventually, they may flow back up with the wash water, and be sprayed on more produce as it passes over the belt.

Since the water is recirculated, microbial levels must be kept low by adding a sanitizer, if you're following the best practices.

Another type of system is the immersion wash.

Instead of wash water spraying down onto produce, items are added to the tank, where they are kept submerged until washing is complete.

Two types of batch systems are shown here.

The diagram on the left shows an immersion system where the wash water goes down the drain and is not reused.

The diagram on the right shows a recirculating immersion wash system.

The water is mechanically pumped back into the tank, so the water is moving past the fruits or vegetables more than once.

Both of these systems require the addition of a sanitizer.

That's because the produce is continuously immersed in the wash water.

As we discussed earlier, if one item is contaminated, there is a chance for microbes to be transferred to the others.

The sanitizer will prevent that from happening.

Here's an example of a small batch immersion wash tank.

It's a simple plastic tub, like the ones you can find at a farm supply store.

Here you can see salad greens being washed.

They should be adding a sanitizer to that wash water, because of the potential for cross-contamination.

When selecting a tank or tub to use, it's best to avoid galvanized metal tanks that have a coating of zinc.

This metal can slowly dissolve in even slightly acidic water, giving a bad flavor to your produce.

It is best to use tanks made of food-grade plastic, stainless steel, or another material that will not change the taste of your product.

Here is an example of a recirculating batch immersion system.

This is a flume tank.

In this case, the water recirculates as it is continuously pumped from the end of the tank to the front.

A sanitizer is added to the water, and the concentration continuously monitored.

We'll explain why monitoring is important in the next video.

Here's another example of a wash tank.

You can see there's a lot of agitation moving the melons along as soil is washed away.

This is just like the previous example.

Because the water is being recirculated, a sanitizer should be added.

Triple washing systems are commonly used to wash produce in fresh-cut processing operations.

For example, most of the bagged salads that you see in a grocery store have been triple washed.

This triple wash system can be adapted for smaller farm operations.

In this method, the produce is washed three separate times.

Each successive step washes more soil off, so that the product coming out of the third wash is exceptionally clean.

Following the best practices we have discussed, any time that produce is immersed in a solution, a sanitizer is required.

Therefore the wash water in all three sinks would require addition of sanitizer.

However, the water in the first sink could easily get muddy very quickly, and that interferes with the effectiveness of the sanitizer.

For this reason, a triple wash system can be modified so that the first sink is a single pass wash.

Water is sprayed from above, down onto and over the produce, and most of the heavy soils and debris are flushed away and down the drain.

Because the produce is never immersed, no sanitizer is necessary.

The produce is then transferred from the first sink to the next sink for a second wash.

In this sink, the produce is immersed, so we need to add a sanitizer to the wash water.

Although much of the soil was removed in the first step, there still may be enough organic matter to interfere with the sanitizer.

For that reason, you should use the highest recommended concentration listed on the label in the second sink, and check its concentration regularly.

The last step, the third sink, is the final rinse.

We still need to add a sanitizer at this step.

The amount of organic matter in the sink will be quite low by now, and less likely to interfere with your sanitizer.

So you can use the lowest effective possible concentration listed on the label, to minimize residual odors on the produce.

This image shows a triple washer in practice at a farm operation.

The wash system has running water in the first sink.

So the sanitizer is optional.

The second and third sinks are batch immersion washes, so sanitizer is required for the second, and is still recommended for the third one, just to prevent the possibility of cross-contamination.

And remember that if you're concerned about possible aromas or off flavors from the sanitizer, you can cut down the sanitizer in that third batch to the lowest effective concentration.

For any type of washing system, it's very important to clean and sanitize the wash tanks at the end of the day.

Look at the picture on the right.

That's a microscopic view of bacteria that have attached to the side of a food contact surface.

They do this by forming a slimy mass called a biofilm.

Bacteria prefer to attach on surfaces, and live in this type of protective community.

It's easy to detect a biofilm.

After emptying the tank or sink, run your finger along the inside.

Does it feel a little slimy?

That's a biofilm.

They physically protect bacteria by preventing sanitizer from reaching the bacteria within, and they can also react with the sanitizer to make it less effective.

So, after each washing you should drain the tank and thoroughly clean it.

You really need to use a scrub brush to remove the biofilm, and then apply a sanitizer to kill the bacteria.

Let the tank air dry before the next use.

These principles apply whether it's a large apple dump tank, or a small plastic tub.

Here is some perspective on just how important it is to eliminate biofilms.

Remember the 2011 outbreak in Colorado that was traced to cantaloupe contaminated with Listeria?

The one that sickened people in 42 states, and caused 33 deaths?

One theory for how this happened is that a sanitizer was not added to the dump tank water.

The investigation found extensive biofilm formation in the tank, which caused each batch of cantaloupes to become contaminated.

A sanitizer in the wash water might have prevented this tragedy.

Remember from our first video that removing surface moisture from produce after washing is a critical step.

As we've discussed, there will always be some bacteria left on washed produce.

If we don't remove as much surface moisture as possible, we're allowing that bacteria to grow, especially if it's kept at a warm temperature.

This can decrease product shelf-life by encouraging growth of spoilage microbes, and possibly make it unsafe to eat.

Do not use reusable cloths or towels to dry produce, because it allows the transfer of microbes from one fruit to another.

Many items like tomatoes, peppers, and tree fruit should be allowed to drip or air dry.

And for leafy greens, you should use a centrifuge.

A salad spinner, the kind you might have in your kitchen to dry lettuce, is a type of centrifuge.

If you use a salad spinner like this at home to dry your lettuce after washing it, the lettuce will keep much longer in the refrigerator than if you leave that extra water on the leaf surfaces.

Centrifuges in commercial operations follow the same principles as the salad spinner.

Here we see how this small scale farm dries greens after washing them.

Those centrifuges work just like a spin dryer.

You can see the white buckets inside that have perforations in them for drainage.

You put the produce in the bucket, close it, and then the centrifuge spins out extra water.

If you are using a centrifuge like this one to dry greens, it's important to store the buckets off the floor, and away from any sources of contamination.

Let them air dry upside down before stacking them together.

Make sure to keep the buckets about six inches off the floor, and four to six inches away from the wall, so that you can see if there are any pests hiding behind them.

Then, they're ready for the next use.

Here's an interesting idea.

You could use a washing machine as a centrifuge for leafy greens, but only if it is cleaned and sanitized before use.

Also, it must be dedicated for that purpose.

That means you should never use it for any other purpose, like washing clothes.

In this picture, you can see they've put the greens in a bag, and then placed the bag directly in the washer.

That will help to minimize damage to the product, and makes it easier to unload.

Oh, and be sure you wash that bag and allow it to dry at the end of each production day.

In the first video of this series, we discussed reasons for washing fresh produce.

In this video, we identified two different kinds of spray wash systems.

Single pass and drain, and multi-pass recirculating.

The first one does not normally require addition of sanitizer to the wash water.

The second one does.

We also discussed single immersion drain and recirculating wash systems.

Both of these require a sanitizer.

The triple wash system can be a combination of both, and the decision to add a sanitizer follows the rules for each.

We also talked about ways you can remove surface moisture, and improve the shelf-life and safety of your product.

In the next video, we'll talk more about sanitizers.

Which ones to use, how wash water quality can affect their anti-microbial properties, and how to make sure they remain active during the washing process.


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