Machines and Equipment

To cool is to take heat away

At the root of every machine sits the principle of refrigeration. Grasp it, and the shape of each machine begins to explain itself.

The starting point matters: to cool is not to add cold, but to take heat away. An evaporating liquid draws heat from its surroundings and leaves them colder — the same principle that makes alcohol feel cool on the palm. A refrigerating machine repeats this evaporation, and the condensation that turns the evaporated refrigerant back into liquid.

To these four parts — compressor, condenser, expansion valve, evaporator — a thermostat is added, governing how much is cooled. Every cold machine in the gelato workshop stands on this same mechanism. The heat gathered at the condenser is shed to air or to water — air-cooled or water-cooled — and the installation site decides the choice.

The four hearts

Along the flow of the process, the machines divide into four broad groups. The steps of Chapters 6 and 7 map onto them directly.

The pasteurizer (pastorizzatore) performs heat pasteurization, homogenization, and aging at 4 °C in one machine (Chapter 6). The mantecatore is the key machine, freezing the mix while stirring it. The blast freezer (abbattitore) carries hardening — it drives the gelato quickly through the critical temperature zone, where ice crystals grow (Chapter 7). And the storage cabinet (conservatore) and the display case (vetrina) guard the built structure in the cold, and serve it at its temperature.

The aging vat — a vessel that frees the pasteurizer

Aging can happen inside the pasteurizer. The four hearts said as much — pasteurization, homogenization, and aging in one machine — and it is true. But what one machine can do, and what one machine is enough for, are different things.

Aging deserves a night (Chapter 6). Through that night the pasteurizer stands occupied as the aging vessel, closed to the next batch. Once a day, no problem. As the batches multiply, the occupation itself becomes the ceiling of production. The reason to own a separate aging vat is not function — it is time.

Cost argues the same way. Between an aging vat and a pasteurizer, the purchase price differs widely, and the running cost sits markedly lower. The usual form is self-standing: connect it to power and it works, its refrigeration unit built in, usually air-cooled.

One divide is easy to miss when choosing: at what temperature the vat can receive the mix. Some types take only mix already cooled — down to about 15 to 20 °C before the transfer. Others accept it still at 80 to 85 °C — vessels that take on the cooling as well, more exactly called cooling-and-aging vats. Choose the former, and the cooling stays with the pasteurizer, so the freeing effect shrinks by that much. Which one fits is decided by how many batches a day the workshop runs.

The place of the aging vat, its costs, and the two receiving types are checked against the technical literature.

The mantecatore — what the type decides

The mantecatore divides into vertical and horizontal, by whether the freezing cylinder stands upright or lies level. In every type, the ice freezing on the cooled surface is scraped away to keep the crystals fine, while air is added. The aim is common. The differences show in what turns, how it is cooled, and what follows the freezing.

The vertical type splits again, into classic and modern. The classic vertical is where this machine began. The tub that takes the mix (sorbettiera) sits immersed in a diathermic liquid, and the tub itself turns on its axis. Extraction is handwork with a spatula, and no signal announces that the gelato is ready — the maker watches, and judges. Artisans still choose this type. They choose it for fruit gelato with pieces, and for stracciatella.

The modern vertical was rebuilt to answer the same affection. Of the old system, only the verticality of the cylinder remains — the tub no longer turns. What turns is the agitator, and the cooling has become direct, with no liquid between. The rebuild lets the door open and the gelato come out with no spatula, and a signal for the moment of extraction has come in.

The horizontal type is simple in operation. Pour the mix through the hopper, choose the program on the panel, start; a signal marks the end. Then open the door, and receive the gelato into a carapina or a vaschetta.

The modern vertical and the horizontal judge the moment of extraction themselves. The method differs from maker to maker. Some measure the hardness of the gelato mechanically. Some infer it from the power the stirring motor draws. Some watch the temperature inside; some combine the data of the refrigeration and the stirring. The aim is one — to catch the best state, and not let it pass. The classic vertical has none of this. The watching eye it demands is a price to count when choosing that type.

The range of capacity is wide. From small machines to large, the general run is 10 to 120 kg per hour. A capacity matched to the workshop's production is what joins quality with economy.

The serving vessel — showing, and guarding

The last vessel of the process is the display case. Under the wide glass and the lights, gelato holds its greatest power to draw. But this vessel was not chosen for the sake of quality.

What once stood at the counter was the pozzetti — lidded cylinders sunk into a coolant. The move from there to the glass display case was an epochal turn for the trade. The reason was one thing: being seen. An old saying of the trade — goods on display are already half sold — names exactly what drove it.

Seen from the side of quality, the story points the other way. The literature gives −14 to −17 °C as the range at which selling cases are customarily calibrated. It then adds that these are not the best temperatures for keeping the structure of the product in good order. The vessel for showing is not the best vessel for guarding — that fact is the starting point.

Further, the inside of a case is not one temperature. Every artisan knows where their own case runs colder and where weaker, and places the flavors accordingly. In recent years, cases with two cooling zones have appeared — on this point, a real step forward.

One more difference deserves attention when making in Japan. The −13 to −14 °C this book placed as the serving temperature came from the structure. It is the point where about eight tenths of the water freezes (Chapter 7). Italian custom, as just seen, sits on the colder side. Meanwhile, Japanese gelato does not ask for as much sweetness as the Italian. Not only the sorbets — the milk-based flavors too tend to hold sugar down. Less sugar means less freezing-point depression, and at the same temperature more of the water freezes. To keep the same ease under the spoon, the temperature moves toward the warm side. This book places −11 to −14 °C as a working guide for practice in Japan. It is a value to confirm on your own formulation and make your own — not a fixed line (Chapter 5).

And the modern vessel is moving to take both. Storage in the manner of the pozzetti, visibility in the manner of the display case. Sealing lids, still cooling, and several working temperatures in one unit are appearing as the answer. The pozzetti was not discarded; its merits are being called back.

The move from pozzetti to display cases, and the customary calibration temperatures, are checked against the technical literature. So are the unevenness inside the case, the two-zone cases, and the modern hybrids. No maker or model is named. The literature gives no figures for the running temperature, the cleaning, or the turnover of the pozzetti, so no numbered comparison of merits is made.

Choosing the machines

No single right answer exists in the choosing, but there are guides.

• Match the production. An oversized machine wastes power and space; an undersized one loses steadiness of quality. Work backward from one day's need.
• Read the site. Air or water for the condenser, the electrical capacity, heat and ventilation, the lines of movement.
• Keep the chain complete. From pasteurization to hardening and storage, assemble the machines so the chain of steps has no break.
• Stay neutral toward makers. Weigh the service network and the certainty of parts supply, not the catalog numbers alone.

"One machine per step" is not the only answer, though. Where the floor of the workshop will not seat every machine, the road of the combined machine has opened. Some pasteurize and freeze in one body; some carry heat, and finish the pasteurization inside the cylinder. And there are builds in which the freezing vessel doubles as the selling vessel — no transfer, and no hardening step at all. Keeping the chain unbroken does not only mean lining up one machine per step. Shortening the chain itself is also a way to solve it.

In a small workshop, floor space and machine count are where the design starts. A combined machine gives up some freedom per step. In return the lines shorten, and the footprint and the first cost lighten. Which way suits is decided by the volume made and the breadth of the menu.

This book recommends no particular product. Any machine, chosen rightly and used rightly, does its work. And the finest machine, used badly and kept badly, is wasted.

Maintenance — a refrigerating machine lives on steady running

Cooling is by now an industrially settled technology. The performance of the refrigerating machine itself can be trusted to a sound product. But keeping the cold rests, for the greater part, on the user.

The key to running a refrigerating machine efficiently and economically is to keep its running steady. A load that spikes and dips wastes efficiency and invites failure. The literature lines up the concrete moves.

• Do not feed it hot mix. Pre-cool with cold water as far as possible before the machine takes over.
• Do not set the storage lower than needed. Every 1 °C off the setting costs about 3 percent of the freezing capacity.
• Defrost the evaporator regularly. Under a coat of ice, the heat cannot leave.
• Brush or vacuum the dust off the condenser, often. And keep its surroundings right — if water-cooled, plenty of water as cold as possible; if air-cooled, no closed corner, fresh air to breathe. Every 1 °C rise in the cooling water or air adds 3 to 4 percent to the compressor's consumption. It also takes about 1 percent off the capacity.
• Keep the fans and the stirrers effective. The fittings of the pasteurizer and the aging vat also set the speed of the heat exchange.
• Cut the openings of the door, and replace the gaskets on schedule. Restraining how often and how long the door opens is, in the words of the literature, no more than a matter of discipline at work. A new gasket usually costs less than the electricity it saves.
• Do not overlight the cabinet. Lamps, too, eat the cold.

Two numbers stand in that list, because the effect of care is not a matter of feeling. In the setting and in the cooling environment alike, one degree counts. This quiet upkeep connects directly to the storage requirement of Chapter 7 — avoid the swings of temperature.

For the storage cabinet, two conditions are decided at the choosing, before any care begins. One is the manner of cooling: still cooling, without a fan, suits storage better. The other is the manner of defrosting. Automatic defrost spares the hands, but while the frost melts, the temperature inside must rise. Even when that rise is momentary, the gelato can break. So for storage, the type defrosted by hand is held the more suitable. These two answer, from the machine's side, the demand of Chapter 7: avoid the swings.

There is, though, another side to the storage temperature. The lower it is held, the better recrystallization is suppressed — and the higher the price in capacity and power. "As low as needed", not "as low as possible" (Chapters 7 and 16).

Here Part II closes. The steps and the machines that turn a formulation into actual gelato are now assembled. Part III stands on this ground and turns to application — to the design of sorbets, to special ingredients, to the developing of flavors.