Pitching yeast into a wine must can be very stressful for these micro-organisms upon which we rely for the production of alcohol. Exposing yeast to changes in temperature, sugar levels, as well as sulfite and nutrient levels causes them stress. If the stress is too much to bear they may go into shock or die off. Creating a yeast starter is the best way to reduce shock and ensure a healthy population is introduced to your wine.
Our job as a winemaker is to make this transition as easy on the yeast as possible so that fermentation gets underway with a healthy and active yeast population. This article assumes you are pitching your own wine yeast and not relying upon wild yeast to make your wine.
In the yeast life cycle, the first phase is concerned with growing the yeast population. Once they reach critical mass alcoholic fermentation gets underway and our must is made into wine. The stronger the initial population introduced to our must, the quicker this first phase will go.
An active and healthy yeast population is also better able to keep unwanted spoilage micro-organisms at bay. When competing for the same resources (i.e. sugar) wine yeast are quite aggressive.
Dry active yeast is the most common form available to winemakers. Just like baking yeast, it is a powder which contains little granules of live yeast. The outside of the granule is a crust of dead yeast cells and food which protects and feeds the living yeast cells inside this crust. Obviously they’re not thriving in those granules as they are provided with only enough food to sustain them in a dormant state.
Tossing dry yeast into a wet environment full of sugar and nutrients and likely at a differenent temperature is an abrupt change in environment. It can take a day or two for the yeast to adjust before the growth phase really starts to take off if pitched this way.
There are better ways to introduce a yeast to a must and we’ll talk about two of them here. The first method is to simply hydrate the yeast so they are out of their crust and available to start consuming sugar. The second method involves creating a yeast starter. It begins with hydration but takes things much further by growing the population in a starter before adding it to the must.
These soft transitions that allow the yeast to acclimate without dying and hit the must fully active and ready to rule the fermentation of your must.
Hydrating Wine Yeast
As the name implies, hydrating is merely getting the yeast out of the crusty granule and loose in water. It involves heating water to a specific temperature and dissolving the yeast in it. This wakes them up and gets them ready to start eating.
Once they are awake again and free to roam they will need food (sugar) within a very few minutes to survive. Ideally a hydrated yeast is moved to a must within 5-10 minutes and with a temperature differential between the yeast and the must of less than 10F (5C).
The intense amount of sugar and nutrients is still going to be a shock but we’ve woken them up and reduced the temperature differential so they can get right to work acclimating themselves to the remaining environmental conditions and starting fermentation.
For more information check out How to Re-Hydrate Yeast.
A yeast starter takes hydration to the next level. You begin by hydrating the yeast but instead of just pitching it straight into your must you take it through a couple soft transitions.
According to the Red Star instruction yous hydrate your yeast in sugared water for 20-25 minutes. That mixture is then mixed with three times as much of your wine must to allow the yeast to acclimate to their new environment including temperature difference, osmotic pressure (pressure on the yeast due to a difference in sugar concentration outside the yeast cell versus inside the cell), and sulfite levels.
Once the yeast has had the chance to adjust to this new solution it may be pitched into the remainder of your must. This subjects the yeast to smaller changes in sugar concentrations and sulfite levels than if you merely hydrated the yeast.
As you can see yeast starters are designed to minimize environmental shocks to the yeast. The point is to have as many healthy, active yeast cells in your must as soon as possible. Just pitching dry yeast into a sugar laden must can result in mass casualties in the yeast population. Pitching a hydrated yeast alleviates temperature differentials but you are still exposing the yeast to changes in sugar (osmotic pressure), nutrient, and sulfite levels.
For all of this science many recipes and all kit manufacturers recommend pitching dry yeast straight into the must and skipping hydration and creating a yeast starter. Why would they do this if it’s harder on the yeast to get going?
Simply put it’s easier to have winemakers toss the dry yeast into the must rather than having them go through all the extra steps involved in hydrating and building a yeast starter. One yeast packet provides enough yeast to ferment up to 8 or 9 gallons while your typical home winemaking recipe or kit wine is 1-6 gallons. Thus you’ve got a little more than you need to get things going, knowing that some will die off due to the shock.
I don’t recommend going through the paces of making a yeast starter when working with kits or even small batches of fruit wines. That being said, if you do plan on graduating from kits to frozen must or fresh grapes, learning to make a starter when working with kits is a good idea. It’s a far less expensive way to learn how to properly introduce yeast to wine must. Learning to do this with your first 100 gallons of juice from grapes is not a good idea.
Please note that there are different ways to make yeast starters and you should refer to the manufacturers recommendations for your particular strain. My intention here was to illustrate why yeast starters are used and the science behind them.