Stone fruit is the most equipment-dependent group in the frozen fruit trade. Berries are washed, sorted and frozen. Pome fruit is peeled and cut. Stone fruit has to have a hard, irregular, tightly-adhering object removed from the middle of soft flesh at several tonnes an hour without leaving fragments behind, and everything else about the specification follows from how well that is done.
Free-stone and cling-stone: the variety decision that comes first
In apricot, peach, plum and cherry alike, varieties differ in how firmly the flesh adheres to the stone. Free-stone varieties release the pit cleanly when the fruit is halved along the suture. Cling-stone varieties do not; the stone has to be cut or punched out, taking flesh with it.
The consequences are commercial, not merely technical.
- Free-stone fruit gives a higher yield of intact halves and a cleaner cut face.
- Cling-stone fruit gives a lower halves yield but is often firmer, holds shape better in cooking, and can be the better choice for a canned or diced product.
- A processor working with mixed intake will produce inconsistent halves regardless of how good the line is.
If your specification is for whole or halved fruit, the variety group belongs in the contract. Asking for high halves yield without specifying free-stone varieties is asking the processor to solve a problem that was decided in the orchard.
The four pitting methods
Rotary cup pitters hold the fruit in a shaped cup and drive a punch or blade through it. Fast, mechanically simple, and the standard for cherry and plum. They require reasonably uniform fruit size, because a cup sized for a large cherry will mis-strike a small one.
Halving and twisting machines cut along the suture and separate the two halves with counter-rotating heads, letting the stone drop. This is the method for apricot and free-stone peach, and it gives the best-looking halves.
Torque or corkscrew pitters grip and rotate the flesh around a fixed stone. Used on cling-stone peach where twisting is the only way to break the adhesion. Yield is lower and the cut face is rougher.
Manual pitting still exists for premium and small-batch lines, particularly on large apricot halves where appearance is the product. It is slow and labour intensive but it produces the highest intact-halves yield.
Each method leaves a different signature in the finished product, which is why a buyer changing supplier should expect a visible difference even at an identical written specification.
Stone fragments are a safety control, not a quality nicety
This is the section that matters most. Residual stone and stone fragments in pitted fruit are a physical hazard. They chip teeth, and in a consumer product they generate the kind of complaint that ends a listing.
The general hygiene obligations in Regulation (EC) No 852/2004 require the operator to identify and control hazards through a HACCP-based system, and in a pitting line the stone fragment step is almost always a critical control point. What a buyer should look for is not a claim of zero fragments, which is not achievable, but evidence of a layered control.
- A pitting machine correctly sized and maintained for the fruit calibre being run.
- Size calibration before the pitter, so the fruit presented is within the machine’s working range.
- Stone detection or density separation after pitting, which exploits the fact that a stone sinks and flesh does not.
- X-ray inspection on the finished pack for lines serving retail or infant products. Metal detection does not find stone.
- A documented verification frequency with records, and a defined action when a fragment is found.
Ask for the verification records rather than the tolerance. A supplier who can show you the log of their hourly check and the last three deviations is in control. A supplier who offers a very low fragment percentage and no records is quoting a specification they have not measured.
Cut format and what it costs
The cut format decision determines yield, price and application in that order.
| Format | Typical use | Yield characteristics |
|---|---|---|
| Whole pitted | Cherry, small plum; retail and bakery | Highest yield, least handling loss |
| Halves | Apricot, peach; dessert, bakery, canning | Good yield on free-stone, poor on cling |
| Quarters | Peach, plum; compote, dairy | Additional cut, small fines increase |
| Slices | Peach, apricot; bakery topping, dessert | Moderate loss, appearance sensitive |
| Dice | Peach, apricot, plum; dairy, fillings | Uses off-spec halves, best value per kilogram |
| Puree | All; beverage, baby food, dairy | Absorbs everything the other formats reject |
The important insight in that table is the relationship between the last two rows and everything above them. Dice and puree are not lower-quality products. They are the outlets for fruit that failed a cosmetic criterion applied further up the line, and they carry the same food safety and compositional requirements. A buyer specifying dice is often getting the same orchard, the same intake and the same freezer as the buyer specifying halves, at a materially lower cost, because they are not paying for appearance they will not use.
Browning, blanching and the additive question
Cut stone fruit browns. Apricot and peach brown fast, plum more slowly, cherry barely at all. Three controls exist and each has a consequence.
Line speed is the cheapest and cleanest: get the cut fruit into the freezer quickly enough that enzymatic browning has no time to develop. This works on a well-designed line and fails on a congested one.
A short blanch denatures the enzyme permanently. It also softens the flesh, which is unacceptable on halves for a dessert application and perfectly fine on dice for a cooked filling.
An ascorbic or citric acid dip is effective and widely used. It is an added ingredient with labelling consequences under Regulation (EU) No 1169/2011 and it should be agreed in the specification, not discovered on a certificate of analysis. For sulphited dried stone fruit the position is different again and is covered in the prune product record.
Freezing stone fruit well
Cut stone fruit presents a large area of exposed, wet, soft flesh. Two things follow. It sticks, so a fluidised bed needs careful loading and often a shorter first pass. And it dehydrates at the surface if held too long in a cold dry air stream before the surface seals.
A well-frozen apricot half thaws with a firm shoulder and a low drip loss figure. A badly-frozen one collapses and releases juice. Because the visual difference in the frozen state is small, drip loss on a controlled thaw is the only reliable acceptance test and it belongs in every stone fruit specification.
Storage is the standard frozen regime, minus 18 degrees Celsius or colder, handled according to the Codex code of practice CXC 8-1976. Stone fruit is more sensitive to temperature cycling than berries because the cut faces glaze visibly.
For the format decision in general, see the IQF and block comparison. For what happens to the fruit that does not make a cut grade, see the puree and concentrate guide.