Troubleshooting chocolate problems

Posted: 9 March 2006 | Eric Schmoyer, R&D Laboratory Manager, R.M. Palmer | 1 comment

Determining the cause of line problems and correcting them without creating excessive down time can be a trying experience. This article will cover some of the more common problems found in chocolate and coating production of hollow, solid, one shot, and enrobed items from pre-molding considerations to demolding of finished product.

Determining the cause of line problems and correcting them without creating excessive down time can be a trying experience. This article will cover some of the more common problems found in chocolate and coating production of hollow, solid, one shot, and enrobed items from pre-molding considerations to demolding of finished product.

Determining the cause of line problems and correcting them without creating excessive down time can be a trying experience. This article will cover some of the more common problems found in chocolate and coating production of hollow, solid, one shot, and enrobed items from pre-molding considerations to demolding of finished product.

The scope of this article includes factors common to chocolate and compound coating production. Some useful criteria to work from can be broken down as the following:

  • STP – Study the process, consult your SOPs (standard operating procedures) and adhere to proper parameters
  • Change only one parameter at a time, noting any changes
  • Watch your time and temperature
  • Document, document, document for future problem solving
  • Trust your Line Technician
  • Don’t be afraid to consult your suppliers

Premolding considerations

This is where you might consider all the necessary parameters prior to starting any run. We use what is referred to as the ‘runbook’. These Standard Operating Procedures (SOPs) pertain to every item – from raw materials to storage parameters – which are accessible to all pertinent individuals. The particular parameters of line production are kept in logs by the Line Technicians at the individual lines. The line logs are detailed records of viscosity, temperatures, line speeds, any problems encountered and corrective measures taken, as well as the results. The following are some examples of problems that a pre-run review might eliminate:

  • Mold mix-ups: In the event of more than one mold style being used for a particular item, you must ensure the correct mold is being used
  • Engineering mix-ups: Ensure you are using the correct layout on the depositor andnozzle plate
  • Coating problems: Ensure you are using the correct viscosity chocolate or coating for the item you planto run
  • Compatibility problems: Ensure that centres and coatings and/or decorations are compatible
  • Allergen issues

Finding out too late that you must shut down to change an entire round of molds or clean a depositor to replace a nozzle plate is a frustrating and avoidable error.

Another consideration is compatibility. Bloom problems can be avoided by assuring fat compatibility between coating or chocolate and decorations in hollow and solid decorated items, and shell to centre in one shot items. The same would apply for colours and flavours.


If you presently use deposited decorations, the following are important observations regarding potential problems. This type of line has a series of heaters, depositors and coolers designed to deposit several different colours prior to the chocolate or coating deposit. The mold is heated, the colour is shot and the mold is then cooled. This process can be repeated several times and is much less labour intensive than the hand tied bows and hand made icing decorations.

Compatibility of fat systems with regard to chocolate or coating bears mentioning at this point – a common problem being binding of pistons and clogging of small nozzles as a result of coating formulation. Whey in a formulation can crystallise on pistons, which may eventually cause seizing. Crystallisation may also occur in fine nozzles resulting in binding and clogging. If formulation of the chocolate or compound is the cause, you may need to reduce the fineness or whey component. Discuss the matter with your supplier regarding altering the fineness specifications. Flow problems and clogging may be rectified using emulsifiers to help reduce yield value. Once again, you may benefit from talking to your suppliers regarding viscosity issues and emulsifier levels.

Sticking decorations can occur for several reasons. When decorations are de-molding properly but not adhering to the chocolate, check the mold reheat temperature parameters prior to chocolate deposit. A reheat temperature set too high at deposit will cause the chocolate to stick in the molds and if the temperature is too low the decorations may not adhere to the chocolate. Ideally, the mold reheat should be in the region of 75 to 85 F – preferably close to chocolate deposit temperature yet not high enough to melt the decorations (simply a quick heating pass). This will ensure slight reheating of decorations for adherence to the chocolate while not overheating cavities, which will cause burning of the chocolate at deposit.

Hollow molding


Holes are generally due to uneven coverage of the cavities and not related to air infusion. Can you localise the holes to a particular item? Larger items may be more likely to develop holes based on the surface area of the piece. A viscosity check would be of benefit; if the viscosity is running a little high you might find the chocolate is not coating the mold properly during vibration, particularly on the larger items. Cut open a finished piece and check the distribution and evenness of the chocolate. A similar problem may occur if the mold is too cold upon deposit of chocolate. This will cause the chocolate or coating to set prematurely resulting in a lopsided piece and potential loss of temper.

How is your temper at deposit? When chocolate is over tempered the viscosity may increase resulting in uneven shell thicknesses and holes. This may require the depositor to be drained and refilled with fresh chocolate. Removing large chocolate ‘floaters’ can help prevent, or at least delay, this type of problem.

Where you add your rework will contribute to tempering related production issues. Pre-melt any rework and metre it into the tempering unit. It may help to add this to the chocolate tank feeding the tempering unit. Make sure the temperature of this tank is high enough to thoroughly melt any rework or returned chocolate from the loop. Questions to ask yourself are whether you have added lecithin or cocoa butter to affect viscosity. Too much lecithin will increase viscosity causing poor coverage of the cavities, resulting in uneven coverage and, potentially, holes. Too much cocoa butter may, conversely, lower viscosity to such a degree that the chocolate will not spread evenly before exiting the vibrating station, resulting in misshapen shells and leaking from cavities.

Pieces stuck in cavities

When the finished pieces do not contract properly and are resistant to removal, sticking may occur at the de-molding station. The mold temperature may be too high prior to deposit, causing the chocolate to burn in the cavity and resulting in sticking work. This may be a recurring process, continually building on the fragments left in the mold. The only corrective action in this instance would be to remove the problem molds and wash or replace them. In contrast, if the mold reheat is too cold, the mold may be too cold at deposit, resulting in improper crystallisation and poor (or no) contraction upon cooling. Regular monitoring of temperatures will assure correct mold preheat temperature.

Sticking can also occur as a result of excessive cooling. Overcooling will result in improper crystallisation and improper contraction. Checking the cooling zone temperatures will ensure the tunnel is not too cold. Ideally, in a three zone cooling set up, zone one should be between 59 and 60 F; zone two should be between 50 and 54 F, and zone three should be between 59 and 62 F with the cooling room slightly higher.

Another potential cause of sticking may be residual wetness due either to improper drying after washing or condensation that collects in cavities. Obviously, molds should be properly dried after washing, but, regarding condensation, chocolate will pick up moisture from air with a relative humidity of 75% or higher (85% in a dark chocolate). This will result in sugar bloom in addition to sticking if the condensation is heavy enough. If this is the problem, it is essential to monitor the relative humidity in the cooling sections, ideally keeping it between 63 and 70%.

Marks and fingerprints

Marks, fingerprints, spots and stains are problems encountered in all production lines. The most common cause is poorly washed molds. This will translate into water spots on candy from improper drying procedures; mineral deposits from untreated water; or even residual chocolate left in cavities after washing.

Fingerprints can be troublesome and may result from rising de-molding room temperature and humidity. Monitoring these parameters will prevent this, so don’t be afraid to check with the de-molders. These individuals are used to a certain ambient feel and will notice any changes in the temperature of the room. Make sure the last zone is not too low (Z1= 59-62, Z2= 50-54, Z3= 59-62) and the relative humidity is properly controlled. Cooled air running 55-58 F should have a relative humidity of 63-70%. It is important to check your temper as poorly tempered chocolate is more prone to marking.

Other considerations

When molding compound coatings, the above rules will apply except for the temperature parameters, which will be different owing to the nature of the fats involved. The coating will be run warmer with no tempering necessary and the vibration and cooling sections will be cooler to shock the coating for contraction, but are prone to the same problems with similar results and solutions.

In the event of a metal detector giving false alarms, check for tiny pieces of foil on the tray or belt. Wipe down the top and underside of the belt, as you may collect a small amount of metal dust, which can cause the metal detector to respond. Check also the sensitivity of the metal detector and keep a log with hourly checks.

Solid molding

Decorations and molds

When decorating solid pieces, problems remain the same, although there is a tendency to find more problems related to fat incompatibility and improper handling.

Depositor vs. flood molding

Depositor molding generally has a vertical depositor and piston arrangement. The pistons open, drawing chocolate into the depositor block; then the rotary valve opens, and the chocolate is shot through a series of nozzles laid out according to the cavities in the mold. Flood molding uses a vertical depositor and valve set up where the chocolate flows into a flood bay at a rate set by a valve at the bottom of the depositor and determined by the operator. The operator controls the flow based on the needs and line speed. The key to success is to ensure constant flow to prevent clogging. Molds move through the flood bay, where the cavities are filled. They are then scraped, proceeding through the vibrating section and into the final cooling tunnel. Depositor molding tends to be less messy and more controllable, though it is initially more expensive to set up.

What are your chocolate specifications? If you are running an item that uses chocolate with a higher milk fat content, flood molding may result in a tail effect with drag marks and a lot of flashing.

Drag marks and tails occur due to high viscosity or poor scraping. The mold moves through the scraper and cavity overflow is scraped and held in the flood bay. If the scraper is bent, nicked, or off-center, the chocolate will not be efficiently scraped leaving lines and marks through the pieces and on the mold itself. These marks then cool, resulting in unattractive marks on the back or the pieces. The excess chocolate outside of the cavity is considered ‘flash’.

Flash can occur in any type of molding and is due to excess chocolate or coating overflowing the cavities. Upon de-molding the flashing falls from the mould or piece, collecting about the area, thus wasting chocolate and creating a cleanliness problem. Depositor molding can help minimise these problems by controlling the shot placement and eliminating excess chocolate between cavities. Installing a static electricity eliminator prior to the depositor shot will also help.

Viscosity is a further problem that can occur with solid molding. Air bubbles, wedge shaped pieces and unfilled cavities, in addition to being indicative of heating, cooling or tempering problems, may be related to viscosity, piece size, vibration or all three. When the viscosity is too high and the piece is large, the chocolate may not fill the cavity properly. Running the line faster than usual may result in shorter vibration time, air bubbles on the piece face and (in some cases) a wedge-shaped appearance. If the mold is too cold upon deposit the chocolate begins to cool, resulting in lumpy, poorly filled out pieces. Bubbles on the face may be a combination of too little vibration and too high a viscosity.

Excessive flash may be caused by improper mold orientation. When flood molding, ensure the moulds are oriented correctly and the scraper is level. If depositing, check the shot placement to ensure it is not off centre.

One shot molding

Depositor issues

Many quality problems stem from improper depositor timing. While some are not necessarily production problems, these issues can generate rework and eat away at valuable line time.

The centre may sometimes bleed through to the face of the piece causing sticking and fouling of cavities. Also, shell thickness on the backs of these pieces will be thicker than usual. Conversely, the centre may bleed through the back of the pieces while the face is thicker than usual. Cutting some pieces may help determine the problem. Checking the dwell/delay and suck back settings will help, as will observing the equipment during the shot. The shell rotary valve should open; the centre rotary valve should open; the centre rotary valve should close; the shell rotary valve should close and you should encounter slight suck-back to break off the shot in preparation for the next deposit. When this sequence does not occur in proper order, problems will ensue.

Does the shell rotary valve open and shoot first? Is there enough time before the centre rotary valve opens? Does the shell rotary valve close too early? Does the centre rotary valve close too late leaving residue in suck back? This will be the first thing in your next cavity. These questions may sound like common sense, but follow the logic and study the process in order to determine where the problem lies. Record any changes and make only one modification at a time.

Temperature differences between shell and centre at deposit can translate into de-molding problems later. Consider a chocolate shell with a centre that is too hot: the chocolate temper will be ruined and even if the pieces do de-mold, the shell will be mushy and dull. The same can happen with compound coating shells and sticking is assured. Cracks in the shell may develop after de-molding as the centre cools. Also, depending on the centre, migration may occur.


Vibration on a one shot item should be minimal, particularly if you have inclusions in the shell. Too much will result in the centre migrating through the back of the piece or being pulled through with the inclusions from the face. Too little may leave bubbles on the face of the piece. In this instance the balance lies in managing viscosity of centre and shell and minimising incorporation of air into either. If you find an air-related problem in the item, check the depositor, localise the problem and trace it to the source. Is the agitator on or even necessary in the depositor? Is the pump speed too high? This can be both the centre or shell supply pump, although generally it is more evident in the centre. Lowering coating supply pump speed and increasing pump run time can minimise air in the system. This ensures a constant, slow, consistent fill as opposed to short bursts, which tend to introduce air. Upon investigation you may find that a slower agitation speed, if possible, or none at all may help resolve an air problem.

Other considerations

Have you noticed a swirling effect in the centre of the piece? This can indicate a lift table problem. If the mold is dropping too quickly, this swirling effect will be more pronounced. Alternatively, if the table is lowered too slowly, the centre will be forced into the cavity resulting in a lump or dome appearance in the centre.

Are you noticing cracks and breakage at de-mold point unrelated to any other parameters? Consider whether the de-molding hammers are set too high. When running a coating item the final cooling temperature zone may be set too low, contributing to brittleness.


Centre temperature

Temperature differences can result in cracking of shell or marring of temper in finished pieces. Make sure the centre is acclimated to the depositing room temperature. When extruding a centre, it is important to ensure the cooling belt is properly acclimated to the temperature parameters of the coating. A centre that is too cold upon coating will cool chocolate quickly resulting in poor crystal formation, giving the finished piece a dull and mushy shell. When coated, a warm centre can contract upon cooling and create cracks in the piece. The temper may also be affected, creating a bloom issue.

Coating problems

When enrobing you may notice a change in the curtain coating viscosity. Ensure that the enrober is being supplied with fresh chocolate and the returned chocolate is properly melted before being reintroduced to the tempering unit. Over-tempering will increase viscosity and produce a dull shell finish. With increased viscosity you may also risk tails and feet on finished pieces. This will manifest as thick bottoms. Check your detail rod setting and the transfer spacing onto the cooling belt. Should feet occur when using a bottomer, check whether the chocolate is too hot or too cold. Is the centre too moist causing it to repel the bottom? Is the coating layer excessive due to a tempering problem? The result will be feet on the enrobed piece. The timing of the wire belt and cooling tunnel belt should be checked to assure there is no pushing or dragging of the pieces.

Air bubbles may be apparent on the coated piece prior to the cooling tunnel. If the coating viscosity is too high you may need to increase vibration and blower velocity to remove the air from the coated piece. Excessive vibration will cause a thinning of the shell and possible break up of the piece. Air may also be introduced via the pump. If every other potential cause has been checked, the pump may be running too fast, thus forcing air into the coating.

Other problems

Streaks on the surface of the piece may be indicative of heat exposure. Problem areas may be blower temperature or the stringer coating supply being too hot. If you are noticing weight problems, look across the belt: check the evenness of vibration and air flow across the belt. These can contribute to uneven weight distribution across the belt.


The above are by no means the only problems encountered in these processes, nor are these the only solutions. Adherence to proper parameters, noting any changes made, and recording the results of those changes for future reference will be of considerable help. When presented with a particularly confounding problem, step back and study the process. Consider time and temperature parameters. The solution may be right in front of you.