Graphical abstract The powder XRD pattern in the figure demonstrates the high quality of MFI samples prepared from very dense gels with stochiometric quantities of silica and template together with appropriate mineralization agents and minimal water content in simple polypropylene bottles at 90 °C in times similar to those involved in conventional syntheses at much higher temperatures. Highlights ► Synthesis of high-silica zeolites below 100 °C using very dense synthesis gels. ► Example: very high-quality MFI zeolite at 90 °C in 3–5 days in high yield. ► Simple, efficient, static reactions using very simple non-pressurized equipment. ► Suitable for bulk syntheses or laboratory demonstration experiments.