The chosen shape must highlight the rich flavours and sweetness in your favourite sweet wine. The defined smaller shapes of these sweet and fortified wine glasses concentrates the aromas of these sweeter wines, plus allowing you to enjoy the complex layers of flavours in equal measure to the level of sugar in each wine.
Shown are numerous smaller wine glasses designed to express dynamics characters. Ignoring the stems and base of the glass; there are common traits to be aware. A prime example is the focused angled bowl of the traditional 'Port' glass. Which captures the bouquet of Port and sweet wines, directing the aroma upward to be appreciated by our primary senses of smell. The shape of wine glass can also lend itself to a range of fine spirits and liqueurs.

 

Please do not pre-judge the Port style wine glass, and assume that the small size will not provide or give respect to the complexity of wine to be served. The complex and spicy flavours found in Tawny (along with aged examples) and Vintage Port wines can be enjoyed at their best in this traditional small sized glass, as they let the wine exhibit subtle flavours along with the rich intensity.
The popular smaller snifter or sipper glass (shown below left) has a unique shape and short stem, designed so that your hand can gently (if you choose) warm the wine between sips - enhancing the aroma and flavour of your favourite fortified wine or liqueur.
The bowl of these sweet style wine glasses will be tapered upward with a slightly narrower opening at the top than the bottom. This shape helps to capture, focus and distribute the wine's aroma toward your nose before it lands on your palate. But more importantly the bowl of the wine glass is designed to only allow a small surface area appropriate to the sweet wine and breathe slowly and it does not require oxygen to soften any characters. It also helps to maintain the wines temperature.
Sauternes and quality dessert wines, require a glass designed to show in equal parts the natural level of acidity in the wines, thus balancing the wine's sweetness, viscosity and luscious finish. Do not be surprised by the generous curved design for quality dessert wine glasses, as the shape accentuates the intensity of ripe, sweet, dried fruit, pastry aromas typical of wines made from grapes affected by botrytis (noble rot).
When choosing a wine glass for your sweet wine, the appropriate glass shape should do three things. The shape should highlight the wine's; appearance, aroma and flavour.
First: - a good wine glass should be made of clear glass (the thickness of the glass will depend upon your budget) - but I would encourage you to choose a glass with the thinnest lip you can afford and also care for if used in restaurants. Avoid choosing glasses that are very thick, cloudy, coloured or have etchings or other decoration, as they will detract from the wine.
Second: - the shape of the bowl should retain and focus the aromas toward your nose at the top of the bowl. It should also allow an appropriate amount of delicate swirling of the wine, so that it can interact with the inside surface of the glass so that you can better smell the delicate aromas. These are all aided by a bowl shape which is big enough to swirl, but in a shape that tends to focus aromas upwards your nose as you sip. Avoid glass shapes which are overly wide, flared excessively at the top or have large outward tapers (e.g. Martini glass).
Third: - the shape and lip of the glass affects how the wine lands and is interpreted by your palate and thus how you taste, experience and enjoy the wine. The appropriate shape needs to focus the wine towards the tip of your tongue. The acute nature of the glass opening and height of the bowl will affect the width and landing volume of sweet wine on your tongue and the sensory receptors engaged. Landing near the very tip of your tongue tends to accentuate the sweetness. And landing on the front third of your tongue (but not quite at the middle) starts to de-emphasize the sweetness and accentuates the wines natural levels of acidity - giving balance and clarity to the wine and the finish.
Most importantly though, the edge or lip of the glass should be as thin and sharp in quality (not in the sense that it can cut your lip) as possible to allow the wine to glide into your mouth smoothly and a constant speed and defined flow. If possible try to avoid glasses with a very thick, rolled lip (like a coffee cup) as this will cause uncontrollable turbulence in the wine as it enters the mouth and landing on the palate with no focus - which will lead to lose in character of the wine you are trying to enjoy, plus mouth-feel and flavours with be disjointed and loose personality, focus and pleasure when paired with cuisine.
Yes - the shape can make a difference to your appreciation and ultimate enjoyment of sweet and fortified wines. Science and years of testing the world over have given us this current information and have proved these results time and time again.
I encourage you to pour a glass of your favourite sweet wine in a Martini glass and an appropriate smaller shaped wine glass and see the results for yourself. You will find it more difficult to discern the natural nuances on the wines aroma and even the flavours will seem diluted in the Martini glass. While this is a dramatic difference in glass shape, as your palate becomes more experienced, you will start to notice subtle differences between one wine glass and another. You will appreciate and enjoy the difference.