The Boston Imbiber

'Sophical Maunderings on Hops and Beer

While a casual observer would venture to say that hops are merely spending their off-season waiting-out the cold, there's a lot more hoppening in the plant than merely weathering the elements. In fact, during the upcoming cold season, our quiescent hops will actually be undergoing a revitalization process. This process, called vernalization, is required by many perennials--including hops. It is a prolonged period of several weeks of COLD temperatures--typically 2-10 degrees C (35-50 degrees F)--which enables the plant to flower in the next season. The concensus among hop researchers is that hops need about six weeks of vernalization at 3 degrees C (about 38 degrees F).

Not very much is known about the plant physiology or molecular biology of vernalization, but some general conclusions have been drawn so far. For instance, vernalization is not an absolute process. Instead, it is a cumulative process that has tradeoffs within time and temperature limits. Thus, vernalization seems to proceed more slowly at warmer temperatures and so would require a longer cold-aging time while colder temperatures induce the vernalizing response more quickly. There does seem to exist a minimum time period and a maximum temperature to induce the effect (although they are not presently known for hops). Also, the temperature-sensing seems to take place in the shoot tips (meristem), while the vernalizing physiological stimulation process is probably systemic. Further, the process is not merely passive. Vernalization is a metabolic process that actively requires oxygen and carbon dioxide. So, while it looks like our hops are just hibernating for the winter, they are secretly preparing themselves to produce the next crop of hop cones for us!

The understanding that we now have was gained at the expense of much sacrifice and high drama. It was Julien Tournois who was experimenting on flowering and sexuality in hops and in hemp in Paris around 1911 who first mentioned daylength as a possible factor in flowering and also the extremely early flowering of plants sown in winter. He was excited by these findings and had planned further experiments. Unfortunately, he was killed at the front shortly after he published these findings in 1913. Gassner was the first to make a systematic analysis of vernalization around 1918. His work was extended by Maximov and several other Russian investigators including Lysenko, who first coined the Russian-equivalent of the term "vernalization." Lysenko also first observed that many winter cereals needed not only vernalization but also long daylengths in order to flower.

In 1928, Lysenko postulated that the process of plant development is independent of growth and takes place in a series of irreversible steps, or phases, which must be completed in a strict sequence. This was his theory of "phasic development." However, around 1936, Gregory and Purvis showed that the effects of vernalization could sometimes be reversed by subsequent high temperatures through a process called "devernalization". Lysenko apparently held great sway in the Russian government, however. Despite the fact that devernalization proved that developmental steps were reversible, the great Russian geneticist N.I. Vavilov was imprisoned for pointing out this contradiction to Lysenko's theory. Also, a plant physiologist named Sabinin was persecuted for trying to present a balanced assessment of Lysenko's contribution to developmental plant physiology. (For further reading, see "The Induction of Flowering," edited by L.T. Evans, Cornell University Press, 1969.)

Now there are several lessons here for us hop gardeners. First, we should count our blessings that we can benefit from all the hard work, suffering and persecution of the researchers who developed the understanding of vernalization (and photoperiodism) by simply surfing the net! Second, those who grow hops in pots and bring them indoors for the winter or the southern gardeners with very mild winters should consider whether their plants are getting sufficient vernalization. If your plants have not been thriving and producing cones, they may be suffering from lack of vernalization. Try putting them in a near-freezing environment for six weeks. If you can't manage that, experiment with a warmer (say refrigerator at 42 degrees Fahrenheit) environment for a longer time. Don't forget to keep the roots moist, well-drained and in the dark. I will be conducting similar experiments here in Arizona and will report my results here in the Imbiber Newsletter. Finally, we can take another lesson from our hoppy friends. Rather than becoming couch potatoes during the colder weather, we should take a cue from our hops and use some of our time and energy for personal renewal and rejuvenation. Then we can start next spring with renewed vigor and energy. One springtime of watching the awesome growth rate of our hop shoots is enough to convince us that vernalization really works!

The Dark Days of Winter are Coming! As we will see, the Dark Days are the days when the vernalization potential is the greatest. Of course the coldest days of the year generally correspond to the days with the least daylight. The decreasing amount of daylight in turn is caused by the sun's decreasing declination (angular distance above the equator) as we move toward winter. This decreasing declination is caused by the combination of the earth's tilt and its position relative to the sun as it makes its way along its solar orbit. The declination reaches a minimum when we arrive at the Winter Solstice--the first day of Winter--on December 21. On this day we receive the least amount of sunshine for the year. Oddly enough, however, the latest sunrise and earliest sunset do not occur on December 21st. Why is this? This is because the solar day is actually longer than 24 hours from about mid-November until about mid-February. This period of time is known as "The Dark Days of Winter." During this time, the Equation of Time is dominant over the declination in determining sunrise and sunset times. The Equation of Time tends to push them both later, while the effect of the declination, of course, is to push the sunrise later and the sunset earlier before December 21 and then reverse after the Winter Solstice. As a result, the earliest sunSET occurs before December 21 while the latest sunRISE occurs after December 21. The Equation of Time is latitude-dependent and has less effect on sunrise and sunset times of higher latitudes, so the earliest sunset and latest sunrise occur closer to the winter solstice as the latitude increases. For example, in the Phoenix area (latitude 33 degrees), the earliest sunset will occur on November 30, l999 while the latest sunrise will occur on January 1, l999. In the Hop Heartland of Yakima, Washington (latitude 46 degrees), the earliest sunset will occur on December 10, l999 while the latest sunrise will occur on December 27, 1999. The lowest temperatures occur in December and January, of course. The 40-year-averaged mean January temperatures are 54 degrees for Phoenix and 30 degrees for Yakima, respectively. Their 40-year-averaged minimum January temperatures are 41 degrees for Phoenix and 22 degrees for Yakima. So even in the darkest days of winter the Phoenix hops will need some help to properly vernalize while the Yakima hops have all the cold weather they need.

The history of some of these observations and their contribution to our modern day culture is something else for us to ponder at this time of year while our hops are undergoing vernalization. The ancient astronomers carefully observed the height of the noonday sun above the horizon, or zenith. As the seasons changed from fall to winter, they noticed that the zenith grew lower and lower. This caused a certain amount of anxiety and consternation, as they weren't sure whether or not the sun would just keep getting lower and finally disappear! (This could be disastrous for the farmers as well as those cultivating classic tans.) The ancients also noticed that the rate of decrease in the sun's zenith slowed as wintertime approached. At some point, the sun's daily decreasing zenith seemed to stop decreasing completely. This later became known as the solstice, from the Latin sol or sun and sticere or "to stand still." After a few days, the sun was observed to start moving higher again, and a great seven-day celebration, or Saturnalia, was declared. Each day's verification that the sun had stopped its downward course and was moving upward again was met with more intense celebrating, feasting and merry-making. The Saturnalia came to a Grand Finale on the seventh day when the start of a New Year was declared. The farmers celebrated the coming of another crop year, and the aristocrats looked forward to another season of working on their tans. So now we have one more thing to celebrate at New Years--the Vernalization of our hops, giving them renewed vigor and flowering potential!

As we enter the Dark Days of Winter and approach the New Year, I hope that we all join our hops in their vernalization efforts to make this a period of fortification and renewal, so that we may approach the New Year and the coming Spring with renewed vigor and energy. Till next time, Happy Holidays and Happy New Year!