Successful Wine Fermentation - Yeast Propagation Part II

See previous Successful Wine Fermentation posts: Introduction, Selecting the Right Yeast (Part I, Part II), Preparing Juice/Must for Fermentation, Indigenous Yeast, Inoculation, Yeast Propagation Part I.

Integrating on-site wine yeast propagation into vintage procedures can be difficult. Specialized equipment and a dedicated staff are required to successfully utilize yeast propagation on a large scale; the larger the facility and the faster the pace of fruit intake, the more demanding a program like this becomes. I have worked at facilities that had a winemaker dedicated solely to managing propagation and fermentation procedures, with several cellar staff members dedicated to this alone.

A winery needs to allocate adequate equipment for yeast propagation; this will be based off several factors including the volume of each batch of juice/must to be inoculated at once (within the day) and the number of yeast strains to be propagated simultaneously. There are specialized tanks for sale that are specifically manufactured for yeast propagation, but wineries without such tanks can modify those on hand easily; full temperature control (hot and cold) and the ability to constantly add oxygen (either via a built-in or mobile sparging unit) are the two most important characteristics. Besides tanks, a pump that is able to handle solids and rather gaseous liquid gently is important; a mono-pump is pretty ideal because it can be run dry (without liquid) and move small volumes against head pressure. I always think having a set of hoses dedicated solely for propagation is important because inoculations with yeast starters need to be completed in a timely fashion and with properly sanitized equipment.

Besides having tanks ready, the appropriate laboratory equipment is necessary for analytically tracking propagation progress and to determine inoculation rates and timing. Along with the ability to conduct basic analyses (brix, pH, TA, free and total SO₂, VA, and YAN), the ability to accurately measure yeast population is necessary. I've used this basic method for cell count determination quite a bit and it seems to give a pretty accurate reading. A note of caution: if using yeast rehydration nutrients during propagation procedures, viability testing will be inaccurate (yeast rehydration nutrients are composed largely of autolyzed yeast cells).

Once all the equipment is prepared, it's time to start propagating some yeast. Part III will discuss starting propagation, building a yeast starter culture, and inoculation calculations and timing.