Seven steps to ensuring safe, consistent cold-pressed bars

Seven steps to ensuring safe, consistent cold-pressed bars

A cold-pressed energy or protein bar implicitly promises the customer safety and health by taking things off the label. The challenge: without chemical preservatives and powerful humectants like salt and sugar, cold pressed bars have a very narrow margin for safety, profitability, and product quality.

How can you operate successfully in that margin? This article offers some answers.

Stability Challenges

Like all shelf-stable foods, cold-pressed bars are governed by the food code. They typically require a water activity less than 0.88 to be considered safe. (Though note that 0.85 is the point at which microbes do not proliferate. To prevent mold, bars must be—and stay— below 0.70 aw).

Manufacturers of cold-pressed bars typically measure water activity as a final release specification to show that the bar will not support the growth of pathogenic bacteria over the course of its shelf life.

So why do so many manufacturers struggle with product consistency? Why do once shelf-stable bars suddenly see a rise in customer complaints for off-tastes and mold issues? Why do soft, chewy bars sometimes come out hard and sticky even though the recipe stays the same?

Complying with the food code is no guarantee of real shelf stability. In this article, we will get to the bottom of these issues and help you address them using science.

Preventing Problems

Using water activity as a release spec is important for safety. But top-performing manufacturers do more to prevent customer complaints and safety issues, predict quality problems before they arise, and prevent issues caused by variation in incoming ingredients.

You might assume that if all the ingredients of the bar are shelf stable, the bar will be too. That assumption can easily lead to shelf life taste/texture issues, mold growth, or worse.

First, the worst: you might end up sickening consumers. Ingredients like peanuts or flour may—and often do—contain low-level microbial contamination. On their own, these ingredients have low water activities where microbes don’t grow, and as long as the contamination isn’t significant enough to cause harm, they are safe. The challenge is that spoilage organisms don’t die at low water activities, they simply become dormant. When low-moisture ingredients are combined with higher moisture ingredients, water will migrate within the new product until all the ingredients come to equilibrium. This could take a low-moisture ingredient, which is safe on its own, into a water activity range where microorganisms could begin to proliferate and become potentially hazardous.

Measuring natural variation

Moisture migration can also cause problems with texture—rubbery almonds, hard, sticky bars—and flavor—rancidity and other off flavors.

Historical safety is no predictor of the future. Other bar manufacturers may use similar ingredients. You may have a history of producing safe products. But natural ingredients have significant variability. Particularly in fructose-rich, fibrous ingredients like dates, figs, and mangoes, moisture content is not a reliable predictor of water activity.  A new crop year or a change in the supplier’s supplier can create safety and quality issues even at large, experienced manufacturing plants.

Clean label challenge

Consumer expectations in this segment may also limit your safety strategies. Layers of food safety strategies protect shelf-stable products from unexpected events like storage at higher than normal temperatures. If you’re looking for a clean label, however, that can cross some of these strategies like preservatives and added sugar off your safety list. In order to produce a safe product, you then need to double down remaining safety tactics like pasteurization, water activity control, and packaging.

What happens if you don’t? In a market snapshot study, we measured the water activity of 18 cold pressed bars we bought from local stores and off the internet. That means we looked at their water activity after they’d been shipped, stored, and shelved. Five of those bars—nearly a third of the samples—had dangerously high water activities, within the range where storage at higher temperatures could cause spoilage microorganisms, particularly salmonella, to grow.

And nearly all our bar samples were flirting with water activities where mold becomes an issue.
Steps for success

Successful cold-pressed bar makers understand and monitor water activity at every step in their process from formulation and ingredient inspection to production, packaging, and shelf life. Here are some of the details of what they do.

  1. Create isotherms on each ingredient before formulating
    • Recommended method: Vapor Sorption Analyzer (large entities might purchase an instrument; most will use lab/consultant services)
    • Time: 2-3 weeks (depends on ingredients; access to METER’S or another isotherm library can speed up the process)
    • Cost: Isotherm library, ingredient isotherms included in some AQUALAB subscriptions; stand-alone isotherm services start at $400 per ingredient.
    • Cold-pressed bars are essentially a mixture of raw ingredients. Isotherms let you predict exactly what will happen when you mix them, giving you control over the safety and quality of your bar.
  2. Set incoming ingredient specifications for both moisture content and water activity
    • Recommended method: use isotherms generated in step 1; food science equations or access to Moisture Analysis Toolkit
    • Time: very little extra time needed
    • Cost: none, beyond cost of isotherms
    • Without baking as a backup, you need to control every bit of moisture that goes into your bar. With both a water activity and a moisture content specification for incoming ingredients, you create the recipe that will give you a consistent result.
  3. Monitor water activity on incoming ingredients
    • Recommended method: AQUALAB 3 (1 minute) or 4TE
    • Time: 1 – 7 minutes depending on instrument
    • Cost: starting at $9,000 for instrument
    • Best practice: require vendors to state water activity on CoA; measure to confirm
    • For cold pressed bars, the essential moment of process control happens as the ingredients are received. Out-of-spec ingredients can easily scrap a batch. Water activity predicts these issues; moisture content can’t. A big change in spec helps you quickly identify changes due to different varieties, growing regions, and crop years so you can address major problems before they shut down production. Access to METER’s isotherm library can help you identify whether your ingredients also need independent moisture content monitoring. As the following data show, some (like blueberries) won’t, and some (like mangos) will.

      Figure 2: Dried blueberries, multiple varieties. Variation as a function of drying process and moisture content-water activity relationship is predictable
  4. If you need moisture content, pick the right moisture content method and calibrate it frequently
    • Recommended method: NIR or AQUALAB 3 Fast Moisture calibrated to an AOAC method such as oven/vacuum oven
    • Time: 1 minute per sample plus time for calibration (NIR) or validation (AQUALAB 3)
    • Cost: Starting at $15,000 for NIR, $9,000 for AQUALAB 3 (instruments can be multi-purposed depending on volume)
    • Moisture content measurements aren’t always necessary for safety and quality purposes, but many manufacturers want them for yield determination or regulation/audit purposes. If you make them, understand what they can and can’t do, and make them right. Whatever you choose, it should be frequently calibrated/validated with a standard method.

      Figure 3: Dried mangos, multiple varieties. Both the sugar level and the fiber of the mango affect water activity. The sugar binds water chemically. The fiber binds water structurally. Fiber content varies significantly depending on variety and can break down over time. One mango with moisture content of 20% has a water activity of 0.45. Another with a moisture content of 12.5% has a water activity of almost 0.7. When added to the mix, this difference could cause quality issues ranging from unacceptable taste/texture to final water activity readings in excess of the safety specification.
  5. Use isotherms to set shelf life and select packaging
    • Recommended method: isotherm on final product (from VSA or generated by lab)
    • Time: 1 week + calculation time
    • Cost: starting at $500/product plus calculation time
    • Shelf life and packaging recommendations are critical links in your food safety chain. The detailed understanding that comes from all your isotherm data lets you specify exactly the packaging you need and scientifically define the correct shelf life.
  6. Use isotherms to evaluate risks of storage under abuse conditions
    • Recommended method: may be included in shelf life and packaging study; perform aw measurements at 3 different temperatures.
    • Time: minimal extra time needed to add calculations to step 5
    • Cost:  additional isotherms at 2 other temperatures; no additional cost if you have a variable-temperature water activity meter (AQUALAB 4TE or equivalent)
    • With the isotherm data you have collected, you will be able to use tools to predict how your product will respond to high temperatures and humidities to account for these potential issues either in your specifications and packaging or in your storage recommendations.
  7. Use a safety and quality specification for final product testing
    • Recommended method: Dew point instrument (AQUALAB 3 or 4TE) for final testing
    • Time: full-accuracy test should be run (1 minute for prediction, 5-7 minutes for complete test)
    • Cost: $9,000 for AQUALAB 3; instruments can be multi-purposed depending on volume
    • Setting the right specification to guarantee a safe and high quality product (and performing proper pasteurization) are the foundation of taking care of your customers. This step is essential, and it works best hand-in-hand with earlier in-process steps that alert you to issues that will cause problems in the final bar. By the time your bar is finished, you should already know that it will pass your final product test.
    • Cold pressed bars are a healthy option. When you control moisture, you address health and safety at its most basic level.


Business Impact

Manufacturer 1: Clean label cold pressed energy bars

Primary natural sweetener: date paste

At start-up, entrepreneur founders determined that since all the ingredients they were mixing together were shelf stable, the final product had to be shelf stable, too.

Early customer complaints about taste and potential mold issues led to scrapping $300,000 worth of bars and 2 months with no inventory to meet extremely high demand. A quick decision to scrap reduced reputation loss, but the cost of failing to do things right from the beginning was high.

Cost of scrap: $300k

Lost revenue (est): $1.5M

Manufacturer 2: Clean label snack bars

Scrapped product: Fig bar

Production (estimated): $50M

Crop failure forced a switch to a new supplier and an unanticipated change in the characteristics of a main ingredient (fig paste) in filled bars.

Result: moisture migration as the bars sat on the shelves, causing overwhelming customer complaints of unacceptable taste and texture. Addressing the problem, the company limited production and was unable to meet demand during 12 weeks of emergency reformulation efforts. Quick response limited reputation damage.

Costs: $8M in lost revenue
In addition, cost of reformulation, reputation damage

Manufacturer 3: Low-carbohydrate, low calorie protein bars

Primary sweeteners: inulin, erythritol

Massive consumer complaints about mold built up over months. The company initially believed the complaints were limited in scope and responded slowly.  Ultimately, the company had to stop production, clear out inventory, and change production processes.

For one full quarter, sales were near zero. Massive brand damage occurred just as a new factory was nearing completion, jeopardizing survival of the company.

Costs: 3 months of lost sales ($17M approx.)
In addition, cost to repair damage and loss of future market share