Pillow plate heat exchangers in breweries and wineries: fermentation cooling and tank thermal control
Why dimple plate technology outperforms conventional jackets for fermentation tank cooling: heat transfer coefficient analysis, CIP cleaning and design criteria for beer and wine production.
Temperature control during fermentation is one of the technical parameters with the greatest influence on the organoleptic profile of the final product in breweries and wineries. The difference between a fermentation proceeding at 12 °C and one that peaks at 18 °C may be the difference between a clean product and one with undesirable ester and fusel alcohol profiles. Pillow plate technology — also known as dimple plate — has progressively replaced half-pipe jackets and conventional annular jackets on next-generation stainless steel fermentation vessels, thanks to thermal, hygienic and constructional advantages that become especially evident in tank volumes exceeding 5,000 litres.
1. Operating principle of the pillow plate (dimple plate)
A pillow plate is a heat exchanger formed by two stainless steel sheets joined at their perimeter and by a regular matrix of resistance spot welds, creating an internal labyrinthine cavity with a very narrow cross-section. When a refrigerant fluid (typically aqueous glycol) circulates through this cavity, the dimple geometry induces local turbulent flow — even at low volumetric flow rates — maximising the internal convection coefficient.
The outer sheet of the pillow plate is welded directly to the surface of the fermentation vessel, so that the tank wall simultaneously serves as the load-bearing structure and the heat transfer surface. The embossed geometry of the dimples distributes the refrigerant pressure uniformly across the entire plate surface, allowing operation at relatively high internal pressures (up to 10–15 bar depending on design and sheet thickness) with minimal material thickness.
2. Technical comparison: pillow plate vs. conventional jackets
| Parameter | Pillow plate (dimple plate) | Half-pipe jacket | Conventional annular jacket |
|---|---|---|---|
| Internal convective coefficient (hi) | High: dimple geometry induces local turbulence. Typical values: 3,000–8,000 W/m²·K. | Moderate-high: tubular flow. 2,000–5,000 W/m²·K. | Low-moderate: wide annular flow, often laminar. 500–2,000 W/m²·K. |
| Cooling distribution across tank surface | Excellent: continuous, uniform coverage of all covered surface. | Good along the pipe length; zones between pipes lack direct contact. | Variable: risk of dead zones in large-section annular circuit. |
| Refrigerant fluid volume in circuit | Very low: narrow flow passage (typically 3–6 mm). Reduced glycol volume in circuit. | Moderate. | High: large annular cross-section. |
| Thermal response time | Very fast: low fluid volume, reduced thermal inertia. Rapid control system response. | Fast-moderate. | Slow: large fluid volume, high thermal inertia. Slow response to setpoint changes. |
| Cleanability — product side | Excellent: smooth external surface in contact with product, suitable for CIP cleaning. | Good. | Good. |
3. Specific applications in breweries and wineries
3.1. Fermentation vessel cooling in brewing
In bottom-fermentation (lager) beer production, temperature control is especially critical because the yeast working window (typically 8–14 °C for standard lager strains) is narrow and the heat generated by alcoholic fermentation is significant: approximately 2.3 kJ are released per gram of fermented sugar. In a 50-hl fermenter with 12 °P wort, the cooling duty required at peak fermentation activity can be between 3 and 8 kW depending on the fermentation rate.
Pillow plates welded to the cylindrical tank wall (and, in some designs, to the cone) allow this heat extraction to be distributed homogeneously, avoiding radial temperature gradients that could create localised sub-cooling zones where yeast activity is inhibited or premature precipitation occurs. The fast response of the system — due to the low refrigerant circuit volume — facilitates the use of PID control systems that maintain temperature setpoints within ±0.5 °C, difficult to achieve with high-inertia conventional jackets.
3.2. Must temperature control in wine fermentation
In white and rosé winemaking, fermentation temperature control (typically between 12 and 18 °C) is critical for preserving volatile varietal aromas that are lost through volatilisation if temperatures are exceeded. Pillow plates on AISI 304 or 316L stainless steel tanks allow low fermentation temperatures to be reached and maintained with modest refrigeration systems. The ability to reach temperatures close to 0 °C uniformly and in a controlled manner — the so-called cold tartrate stabilisation — is an application that highlights the thermal performance of pillow plate technology over less efficient alternatives.
3.3. Craft breweries and microbreweries
In craft breweries with smaller fermenters (100–2,000 litres), pillow plate technology offers additional advantages due to its compatibility with relatively small glycol systems and the ease of integration on cylindroconical stainless steel tanks. The typical configuration consists of one or two independent pillow plate zones (cylindrical and conical sections) connected to a glycol circuit with independent zone control valves, allowing programmable temperature profiles throughout fermentation.
4. Pillow plate sizing criteria for fermentation vessels
- Peak fermentation thermal duty (Qmax): estimated from fermentation rate, wort concentration (°P or °Brix) and tank volume. In beer production, indicative reference values range from 50 to 150 W per hl of fermenter capacity at peak activity, depending on the recipe and yeast used.
- Available temperature differential (ΔT): difference between fermenting product temperature and refrigerant inlet temperature to the plate.
- Minimum refrigerant temperature: in aqueous glycol circuits, glycol temperatures of -2 to -5 °C are generally sufficient for most standard fermentation applications; lower temperatures are used for tartrate stabilisation.
- Tank surface coverage: the proportion of the total tank surface covered with pillow plate (typically 40–70 % of the lateral surface) must be sufficient to ensure cooling uniformity and avoid vertical temperature gradients in the product.
- Refrigerant circuit working pressure: pillow plate design must be validated for the maximum glycol circuit pressure. In indirect glycol circuits, typical working pressures are 3–6 bar.
5. Materials and food hygiene requirements
| Component | Typical material | Hygiene and regulatory considerations |
|---|---|---|
| Outer plate sheet (product side / tank exterior) | AISI 304 (1.4301) or AISI 316L (1.4404) | Surface finish Ra ≤ 0.8 µm in zones adjacent to product. AISI 316L recommended in environments with aggressive chloride-containing CIP cleaning or in high-acidity wine production. |
| Inner plate sheet (refrigerant side) | AISI 304 or AISI 316L | Not in contact with product; material selected for compatibility with refrigerant fluid. In ammonia or CO₂ circuits, validate material compatibility with the refrigerant. |
| Refrigerant circuit connections | Sanitary fittings (DIN 11851, SMS, Tri-Clamp) in zones near product. | In zones where a refrigerant leak could contaminate the product, use certified fittings and food-grade refrigerant fluid (propylene glycol, USP grade). |
6. CIP cleaning of tanks with pillow plates
CIP cleaning of fermentation vessels equipped with pillow plates acts on the internal face of the tank (product side) and does not contact the pillow plates, which are located on the exterior.
- Exterior tank wall surface between plate zones: tank wall areas not covered by pillow plates must be accessible for external cleaning and periodic visual inspection. Moisture and dirt accumulation at pillow plate perimeter welds can be a site of external corrosion if not managed properly.
- Periodic pillow plate integrity inspection: a periodic hydrostatic pressure test of the plate circuit allows early detection of internal leaks before they can contaminate either the product or the refrigerant circuit.
- Refrigerant circuit purging during extended shutdowns: during seasonal or prolonged maintenance shutdowns, it is recommended to fully drain the glycol circuit from the plates to prevent refrigerant fluid degradation and microbial growth inside the plate in static fluid conditions.
One of the less documented advantages of pillow plate technology in breweries and wineries is the ability to increase the cooling capacity of an existing vessel without replacing it. If the control system detects that current plate capacity is insufficient for a new production volume or a more active fermentation recipe, it is technically possible to add additional pillow plate zones on available tank surface, provided the tank wall is in good condition and new welds are performed by qualified personnel following approved welding procedures for stainless steel in food service.